-Upgraded webp to a MUCH newer version. Hoping it fixes some bugs in the process. Keeping old version just in case for now.

-Added ability to convert xml and tscn scenes to binary on export, makes loading of larger scenes faster

21 files changed, 5135 insertions, 4579 deletions

diff --git a/drivers/webp/enc/alpha.c b/drivers/webp/enc/alpha.c
index e554eb7f30..fad6346e43 100644
--- a/drivers/webp/enc/alpha.c
+++ b/drivers/webp/enc/alpha.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Alpha-plane compression.
@@ -13,13 +15,11 @@
 #include <stdlib.h>
 
 #include "./vp8enci.h"
+#include "../dsp/dsp.h"
 #include "../utils/filters.h"
 #include "../utils/quant_levels.h"
-#include "../format_constants.h"
-
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
+#include "../utils/utils.h"
+#include "../webp/format_constants.h"
 
 // -----------------------------------------------------------------------------
 // Encodes the given alpha data via specified compression method 'method'.
@@ -36,7 +36,7 @@ extern "C" {
 //
 // 'output' corresponds to the buffer containing compressed alpha data.
 //          This buffer is allocated by this method and caller should call
-//          free(*output) when done.
+//          WebPSafeFree(*output) when done.
 // 'output_size' corresponds to size of this compressed alpha buffer.
 //
 // Returns 1 on successfully encoding the alpha and
@@ -48,12 +48,11 @@ extern "C" {
 
 static int EncodeLossless(const uint8_t* const data, int width, int height,
                           int effort_level,  // in [0..6] range
-                          VP8BitWriter* const bw,
+                          VP8LBitWriter* const bw,
                           WebPAuxStats* const stats) {
   int ok = 0;
   WebPConfig config;
   WebPPicture picture;
-  VP8LBitWriter tmp_bw;
 
   WebPPictureInit(&picture);
   picture.width = width;
@@ -63,53 +62,51 @@ static int EncodeLossless(const uint8_t* const data, int width, int height,
   if (!WebPPictureAlloc(&picture)) return 0;
 
   // Transfer the alpha values to the green channel.
-  {
-    int i, j;
-    uint32_t* dst = picture.argb;
-    const uint8_t* src = data;
-    for (j = 0; j < picture.height; ++j) {
-      for (i = 0; i < picture.width; ++i) {
-        dst[i] = (src[i] << 8) | 0xff000000u;
-      }
-      src += width;
-      dst += picture.argb_stride;
-    }
-  }
+  WebPDispatchAlphaToGreen(data, width, picture.width, picture.height,
+                           picture.argb, picture.argb_stride);
 
   WebPConfigInit(&config);
   config.lossless = 1;
   config.method = effort_level;  // impact is very small
-  // Set moderate default quality setting for alpha. Higher qualities (80 and
-  // above) could be very slow.
-  config.quality = 10.f + 15.f * effort_level;
-  if (config.quality > 100.f) config.quality = 100.f;
+  // Set a low default quality for encoding alpha. Ensure that Alpha quality at
+  // lower methods (3 and below) is less than the threshold for triggering
+  // costly 'BackwardReferencesTraceBackwards'.
+  config.quality = 8.f * effort_level;
+  assert(config.quality >= 0 && config.quality <= 100.f);
 
-  ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);
-  ok = ok && (VP8LEncodeStream(&config, &picture, &tmp_bw) == VP8_ENC_OK);
+  ok = (VP8LEncodeStream(&config, &picture, bw) == VP8_ENC_OK);
   WebPPictureFree(&picture);
-  if (ok) {
-    const uint8_t* const data = VP8LBitWriterFinish(&tmp_bw);
-    const size_t data_size = VP8LBitWriterNumBytes(&tmp_bw);
-    VP8BitWriterAppend(bw, data, data_size);
+  ok = ok && !bw->error_;
+  if (!ok) {
+    VP8LBitWriterWipeOut(bw);
+    return 0;
   }
-  VP8LBitWriterDestroy(&tmp_bw);
-  return ok && !bw->error_;
+  return 1;
 }
 
 // -----------------------------------------------------------------------------
 
+// Small struct to hold the result of a filter mode compression attempt.
+typedef struct {
+  size_t score;
+  VP8BitWriter bw;
+  WebPAuxStats stats;
+} FilterTrial;
+
+// This function always returns an initialized 'bw' object, even upon error.
 static int EncodeAlphaInternal(const uint8_t* const data, int width, int height,
                                int method, int filter, int reduce_levels,
                                int effort_level,  // in [0..6] range
                                uint8_t* const tmp_alpha,
-                               VP8BitWriter* const bw,
-                               WebPAuxStats* const stats) {
+                               FilterTrial* result) {
   int ok = 0;
   const uint8_t* alpha_src;
   WebPFilterFunc filter_func;
   uint8_t header;
-  size_t expected_size;
   const size_t data_size = width * height;
+  const uint8_t* output = NULL;
+  size_t output_size = 0;
+  VP8LBitWriter tmp_bw;
 
   assert((uint64_t)data_size == (uint64_t)width * height);  // as per spec
   assert(filter >= 0 && filter < WEBP_FILTER_LAST);
@@ -118,43 +115,163 @@ static int EncodeAlphaInternal(const uint8_t* const data, int width, int height,
   assert(sizeof(header) == ALPHA_HEADER_LEN);
   // TODO(skal): have a common function and #define's to validate alpha params.
 
-  expected_size =
-      (method == ALPHA_NO_COMPRESSION) ? (ALPHA_HEADER_LEN + data_size)
-                                       : (data_size >> 5);
-  header = method | (filter << 2);
-  if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4;
-
-  VP8BitWriterInit(bw, expected_size);
-  VP8BitWriterAppend(bw, &header, ALPHA_HEADER_LEN);
-
   filter_func = WebPFilters[filter];
-  if (filter_func) {
-    filter_func(data, width, height, 1, width, tmp_alpha);
+  if (filter_func != NULL) {
+    filter_func(data, width, height, width, tmp_alpha);
     alpha_src = tmp_alpha;
   }  else {
     alpha_src = data;
   }
 
+  if (method != ALPHA_NO_COMPRESSION) {
+    ok = VP8LBitWriterInit(&tmp_bw, data_size >> 3);
+    ok = ok && EncodeLossless(alpha_src, width, height, effort_level,
+                              &tmp_bw, &result->stats);
+    if (ok) {
+      output = VP8LBitWriterFinish(&tmp_bw);
+      output_size = VP8LBitWriterNumBytes(&tmp_bw);
+      if (output_size > data_size) {
+        // compressed size is larger than source! Revert to uncompressed mode.
+        method = ALPHA_NO_COMPRESSION;
+        VP8LBitWriterWipeOut(&tmp_bw);
+      }
+    } else {
+      VP8LBitWriterWipeOut(&tmp_bw);
+      return 0;
+    }
+  }
+
   if (method == ALPHA_NO_COMPRESSION) {
-    ok = VP8BitWriterAppend(bw, alpha_src, width * height);
-    ok = ok && !bw->error_;
-  } else {
-    ok = EncodeLossless(alpha_src, width, height, effort_level, bw, stats);
-    VP8BitWriterFinish(bw);
+    output = alpha_src;
+    output_size = data_size;
+    ok = 1;
+  }
+
+  // Emit final result.
+  header = method | (filter << 2);
+  if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4;
+
+  VP8BitWriterInit(&result->bw, ALPHA_HEADER_LEN + output_size);
+  ok = ok && VP8BitWriterAppend(&result->bw, &header, ALPHA_HEADER_LEN);
+  ok = ok && VP8BitWriterAppend(&result->bw, output, output_size);
+
+  if (method != ALPHA_NO_COMPRESSION) {
+    VP8LBitWriterWipeOut(&tmp_bw);
   }
+  ok = ok && !result->bw.error_;
+  result->score = VP8BitWriterSize(&result->bw);
   return ok;
 }
 
 // -----------------------------------------------------------------------------
 
-// TODO(skal): move to dsp/ ?
-static void CopyPlane(const uint8_t* src, int src_stride,
-                      uint8_t* dst, int dst_stride, int width, int height) {
-  while (height-- > 0) {
-    memcpy(dst, src, width);
-    src += src_stride;
-    dst += dst_stride;
+static int GetNumColors(const uint8_t* data, int width, int height,
+                        int stride) {
+  int j;
+  int colors = 0;
+  uint8_t color[256] = { 0 };
+
+  for (j = 0; j < height; ++j) {
+    int i;
+    const uint8_t* const p = data + j * stride;
+    for (i = 0; i < width; ++i) {
+      color[p[i]] = 1;
+    }
+  }
+  for (j = 0; j < 256; ++j) {
+    if (color[j] > 0) ++colors;
   }
+  return colors;
+}
+
+#define FILTER_TRY_NONE (1 << WEBP_FILTER_NONE)
+#define FILTER_TRY_ALL ((1 << WEBP_FILTER_LAST) - 1)
+
+// Given the input 'filter' option, return an OR'd bit-set of filters to try.
+static uint32_t GetFilterMap(const uint8_t* alpha, int width, int height,
+                             int filter, int effort_level) {
+  uint32_t bit_map = 0U;
+  if (filter == WEBP_FILTER_FAST) {
+    // Quick estimate of the best candidate.
+    int try_filter_none = (effort_level > 3);
+    const int kMinColorsForFilterNone = 16;
+    const int kMaxColorsForFilterNone = 192;
+    const int num_colors = GetNumColors(alpha, width, height, width);
+    // For low number of colors, NONE yields better compression.
+    filter = (num_colors <= kMinColorsForFilterNone)
+        ? WEBP_FILTER_NONE
+        : WebPEstimateBestFilter(alpha, width, height, width);
+    bit_map |= 1 << filter;
+    // For large number of colors, try FILTER_NONE in addition to the best
+    // filter as well.
+    if (try_filter_none || num_colors > kMaxColorsForFilterNone) {
+      bit_map |= FILTER_TRY_NONE;
+    }
+  } else if (filter == WEBP_FILTER_NONE) {
+    bit_map = FILTER_TRY_NONE;
+  } else {  // WEBP_FILTER_BEST -> try all
+    bit_map = FILTER_TRY_ALL;
+  }
+  return bit_map;
+}
+
+static void InitFilterTrial(FilterTrial* const score) {
+  score->score = (size_t)~0U;
+  VP8BitWriterInit(&score->bw, 0);
+}
+
+static int ApplyFiltersAndEncode(const uint8_t* alpha, int width, int height,
+                                 size_t data_size, int method, int filter,
+                                 int reduce_levels, int effort_level,
+                                 uint8_t** const output,
+                                 size_t* const output_size,
+                                 WebPAuxStats* const stats) {
+  int ok = 1;
+  FilterTrial best;
+  uint32_t try_map =
+      GetFilterMap(alpha, width, height, filter, effort_level);
+  InitFilterTrial(&best);
+
+  if (try_map != FILTER_TRY_NONE) {
+    uint8_t* filtered_alpha =  (uint8_t*)WebPSafeMalloc(1ULL, data_size);
+    if (filtered_alpha == NULL) return 0;
+
+    for (filter = WEBP_FILTER_NONE; ok && try_map; ++filter, try_map >>= 1) {
+      if (try_map & 1) {
+        FilterTrial trial;
+        ok = EncodeAlphaInternal(alpha, width, height, method, filter,
+                                 reduce_levels, effort_level, filtered_alpha,
+                                 &trial);
+        if (ok && trial.score < best.score) {
+          VP8BitWriterWipeOut(&best.bw);
+          best = trial;
+        } else {
+          VP8BitWriterWipeOut(&trial.bw);
+        }
+      }
+    }
+    WebPSafeFree(filtered_alpha);
+  } else {
+    ok = EncodeAlphaInternal(alpha, width, height, method, WEBP_FILTER_NONE,
+                             reduce_levels, effort_level, NULL, &best);
+  }
+  if (ok) {
+    if (stats != NULL) {
+      stats->lossless_features = best.stats.lossless_features;
+      stats->histogram_bits = best.stats.histogram_bits;
+      stats->transform_bits = best.stats.transform_bits;
+      stats->cache_bits = best.stats.cache_bits;
+      stats->palette_size = best.stats.palette_size;
+      stats->lossless_size = best.stats.lossless_size;
+      stats->lossless_hdr_size = best.stats.lossless_hdr_size;
+      stats->lossless_data_size = best.stats.lossless_data_size;
+    }
+    *output_size = VP8BitWriterSize(&best.bw);
+    *output = VP8BitWriterBuf(&best.bw);
+  } else {
+    VP8BitWriterWipeOut(&best.bw);
+  }
+  return ok;
 }
 
 static int EncodeAlpha(VP8Encoder* const enc,
@@ -187,13 +304,18 @@ static int EncodeAlpha(VP8Encoder* const enc,
     return 0;
   }
 
-  quant_alpha = (uint8_t*)malloc(data_size);
+  if (method == ALPHA_NO_COMPRESSION) {
+    // Don't filter, as filtering will make no impact on compressed size.
+    filter = WEBP_FILTER_NONE;
+  }
+
+  quant_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size);
   if (quant_alpha == NULL) {
     return 0;
   }
 
   // Extract alpha data (width x height) from raw_data (stride x height).
-  CopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height);
+  WebPCopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height);
 
   if (reduce_levels) {  // No Quantization required for 'quality = 100'.
     // 16 alpha levels gives quite a low MSE w.r.t original alpha plane hence
@@ -205,126 +327,99 @@ static int EncodeAlpha(VP8Encoder* const enc,
   }
 
   if (ok) {
-    VP8BitWriter bw;
-    int test_filter;
-    uint8_t* filtered_alpha = NULL;
-
-    // We always test WEBP_FILTER_NONE first.
-    ok = EncodeAlphaInternal(quant_alpha, width, height,
-                             method, WEBP_FILTER_NONE, reduce_levels,
-                             effort_level, NULL, &bw, pic->stats);
-    if (!ok) {
-      VP8BitWriterWipeOut(&bw);
-      goto End;
-    }
-
-    if (filter == WEBP_FILTER_FAST) {  // Quick estimate of a second candidate?
-      filter = EstimateBestFilter(quant_alpha, width, height, width);
-    }
-    // Stop?
-    if (filter == WEBP_FILTER_NONE) {
-      goto Ok;
-    }
-
-    filtered_alpha = (uint8_t*)malloc(data_size);
-    ok = (filtered_alpha != NULL);
-    if (!ok) {
-      goto End;
+    VP8FiltersInit();
+    ok = ApplyFiltersAndEncode(quant_alpha, width, height, data_size, method,
+                               filter, reduce_levels, effort_level, output,
+                               output_size, pic->stats);
+    if (pic->stats != NULL) {  // need stats?
+      pic->stats->coded_size += (int)(*output_size);
+      enc->sse_[3] = sse;
     }
-
-    // Try the other mode(s).
-    {
-      WebPAuxStats best_stats;
-      size_t best_score = VP8BitWriterSize(&bw);
-
-      memset(&best_stats, 0, sizeof(best_stats));  // prevent spurious warning
-      if (pic->stats != NULL) best_stats = *pic->stats;
-      for (test_filter = WEBP_FILTER_HORIZONTAL;
-           ok && (test_filter <= WEBP_FILTER_GRADIENT);
-           ++test_filter) {
-        VP8BitWriter tmp_bw;
-        if (filter != WEBP_FILTER_BEST && test_filter != filter) {
-          continue;
-        }
-        ok = EncodeAlphaInternal(quant_alpha, width, height,
-                                 method, test_filter, reduce_levels,
-                                 effort_level, filtered_alpha, &tmp_bw,
-                                 pic->stats);
-        if (ok) {
-          const size_t score = VP8BitWriterSize(&tmp_bw);
-          if (score < best_score) {
-            // swap bitwriter objects.
-            VP8BitWriter tmp = tmp_bw;
-            tmp_bw = bw;
-            bw = tmp;
-            best_score = score;
-            if (pic->stats != NULL) best_stats = *pic->stats;
-          }
-        } else {
-          VP8BitWriterWipeOut(&bw);
-        }
-        VP8BitWriterWipeOut(&tmp_bw);
-      }
-      if (pic->stats != NULL) *pic->stats = best_stats;
-    }
- Ok:
-    if (ok) {
-      *output_size = VP8BitWriterSize(&bw);
-      *output = VP8BitWriterBuf(&bw);
-      if (pic->stats != NULL) {         // need stats?
-        pic->stats->coded_size += (int)(*output_size);
-        enc->sse_[3] = sse;
-      }
-    }
-    free(filtered_alpha);
   }
- End:
-  free(quant_alpha);
+
+  WebPSafeFree(quant_alpha);
   return ok;
 }
 
-
 //------------------------------------------------------------------------------
 // Main calls
 
+static int CompressAlphaJob(VP8Encoder* const enc, void* dummy) {
+  const WebPConfig* config = enc->config_;
+  uint8_t* alpha_data = NULL;
+  size_t alpha_size = 0;
+  const int effort_level = config->method;  // maps to [0..6]
+  const WEBP_FILTER_TYPE filter =
+      (config->alpha_filtering == 0) ? WEBP_FILTER_NONE :
+      (config->alpha_filtering == 1) ? WEBP_FILTER_FAST :
+                                       WEBP_FILTER_BEST;
+  if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression,
+                   filter, effort_level, &alpha_data, &alpha_size)) {
+    return 0;
+  }
+  if (alpha_size != (uint32_t)alpha_size) {  // Sanity check.
+    WebPSafeFree(alpha_data);
+    return 0;
+  }
+  enc->alpha_data_size_ = (uint32_t)alpha_size;
+  enc->alpha_data_ = alpha_data;
+  (void)dummy;
+  return 1;
+}
+
 void VP8EncInitAlpha(VP8Encoder* const enc) {
+  WebPInitAlphaProcessing();
   enc->has_alpha_ = WebPPictureHasTransparency(enc->pic_);
   enc->alpha_data_ = NULL;
   enc->alpha_data_size_ = 0;
+  if (enc->thread_level_ > 0) {
+    WebPWorker* const worker = &enc->alpha_worker_;
+    WebPGetWorkerInterface()->Init(worker);
+    worker->data1 = enc;
+    worker->data2 = NULL;
+    worker->hook = (WebPWorkerHook)CompressAlphaJob;
+  }
 }
 
-int VP8EncFinishAlpha(VP8Encoder* const enc) {
+int VP8EncStartAlpha(VP8Encoder* const enc) {
   if (enc->has_alpha_) {
-    const WebPConfig* config = enc->config_;
-    uint8_t* tmp_data = NULL;
-    size_t tmp_size = 0;
-    const int effort_level = config->method;  // maps to [0..6]
-    const WEBP_FILTER_TYPE filter =
-        (config->alpha_filtering == 0) ? WEBP_FILTER_NONE :
-        (config->alpha_filtering == 1) ? WEBP_FILTER_FAST :
-                                         WEBP_FILTER_BEST;
-
-    if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression,
-                     filter, effort_level, &tmp_data, &tmp_size)) {
-      return 0;
+    if (enc->thread_level_ > 0) {
+      WebPWorker* const worker = &enc->alpha_worker_;
+      // Makes sure worker is good to go.
+      if (!WebPGetWorkerInterface()->Reset(worker)) {
+        return 0;
+      }
+      WebPGetWorkerInterface()->Launch(worker);
+      return 1;
+    } else {
+      return CompressAlphaJob(enc, NULL);   // just do the job right away
     }
-    if (tmp_size != (uint32_t)tmp_size) {  // Sanity check.
-      free(tmp_data);
-      return 0;
+  }
+  return 1;
+}
+
+int VP8EncFinishAlpha(VP8Encoder* const enc) {
+  if (enc->has_alpha_) {
+    if (enc->thread_level_ > 0) {
+      WebPWorker* const worker = &enc->alpha_worker_;
+      if (!WebPGetWorkerInterface()->Sync(worker)) return 0;  // error
     }
-    enc->alpha_data_size_ = (uint32_t)tmp_size;
-    enc->alpha_data_ = tmp_data;
   }
   return WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
 }
 
-void VP8EncDeleteAlpha(VP8Encoder* const enc) {
-  free(enc->alpha_data_);
+int VP8EncDeleteAlpha(VP8Encoder* const enc) {
+  int ok = 1;
+  if (enc->thread_level_ > 0) {
+    WebPWorker* const worker = &enc->alpha_worker_;
+    // finish anything left in flight
+    ok = WebPGetWorkerInterface()->Sync(worker);
+    // still need to end the worker, even if !ok
+    WebPGetWorkerInterface()->End(worker);
+  }
+  WebPSafeFree(enc->alpha_data_);
   enc->alpha_data_ = NULL;
   enc->alpha_data_size_ = 0;
   enc->has_alpha_ = 0;
+  return ok;
 }
-
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/analysis.c b/drivers/webp/enc/analysis.c
index 22cfb492e7..b55128fd48 100644
--- a/drivers/webp/enc/analysis.c
+++ b/drivers/webp/enc/analysis.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Macroblock analysis
@@ -17,16 +19,8 @@
 #include "./cost.h"
 #include "../utils/utils.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 #define MAX_ITERS_K_MEANS  6
 
-static int ClipAlpha(int alpha) {
-  return alpha < 0 ? 0 : alpha > 255 ? 255 : alpha;
-}
-
 //------------------------------------------------------------------------------
 // Smooth the segment map by replacing isolated block by the majority of its
 // neighbours.
@@ -36,7 +30,7 @@ static void SmoothSegmentMap(VP8Encoder* const enc) {
   const int w = enc->mb_w_;
   const int h = enc->mb_h_;
   const int majority_cnt_3_x_3_grid = 5;
-  uint8_t* const tmp = (uint8_t*)WebPSafeMalloc((uint64_t)w * h, sizeof(*tmp));
+  uint8_t* const tmp = (uint8_t*)WebPSafeMalloc(w * h, sizeof(*tmp));
   assert((uint64_t)(w * h) == (uint64_t)w * h);   // no overflow, as per spec
 
   if (tmp == NULL) return;
@@ -57,6 +51,7 @@ static void SmoothSegmentMap(VP8Encoder* const enc) {
       for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
         if (cnt[n] >= majority_cnt_3_x_3_grid) {
           majority_seg = n;
+          break;
         }
       }
       tmp[x + y * w] = majority_seg;
@@ -68,54 +63,14 @@ static void SmoothSegmentMap(VP8Encoder* const enc) {
       mb->segment_ = tmp[x + y * w];
     }
   }
-  free(tmp);
+  WebPSafeFree(tmp);
 }
 
 //------------------------------------------------------------------------------
-// Finalize Segment probability based on the coding tree
-
-static int GetProba(int a, int b) {
-  int proba;
-  const int total = a + b;
-  if (total == 0) return 255;  // that's the default probability.
-  proba = (255 * a + total / 2) / total;
-  return proba;
-}
-
-static void SetSegmentProbas(VP8Encoder* const enc) {
-  int p[NUM_MB_SEGMENTS] = { 0 };
-  int n;
-
-  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
-    const VP8MBInfo* const mb = &enc->mb_info_[n];
-    p[mb->segment_]++;
-  }
-  if (enc->pic_->stats) {
-    for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
-      enc->pic_->stats->segment_size[n] = p[n];
-    }
-  }
-  if (enc->segment_hdr_.num_segments_ > 1) {
-    uint8_t* const probas = enc->proba_.segments_;
-    probas[0] = GetProba(p[0] + p[1], p[2] + p[3]);
-    probas[1] = GetProba(p[0], p[1]);
-    probas[2] = GetProba(p[2], p[3]);
-
-    enc->segment_hdr_.update_map_ =
-        (probas[0] != 255) || (probas[1] != 255) || (probas[2] != 255);
-    enc->segment_hdr_.size_ =
-      p[0] * (VP8BitCost(0, probas[0]) + VP8BitCost(0, probas[1])) +
-      p[1] * (VP8BitCost(0, probas[0]) + VP8BitCost(1, probas[1])) +
-      p[2] * (VP8BitCost(1, probas[0]) + VP8BitCost(0, probas[2])) +
-      p[3] * (VP8BitCost(1, probas[0]) + VP8BitCost(1, probas[2]));
-  } else {
-    enc->segment_hdr_.update_map_ = 0;
-    enc->segment_hdr_.size_ = 0;
-  }
-}
+// set segment susceptibility alpha_ / beta_
 
 static WEBP_INLINE int clip(int v, int m, int M) {
-  return v < m ? m : v > M ? M : v;
+  return (v < m) ? m : (v > M) ? M : v;
 }
 
 static void SetSegmentAlphas(VP8Encoder* const enc,
@@ -142,28 +97,77 @@ static void SetSegmentAlphas(VP8Encoder* const enc,
 }
 
 //------------------------------------------------------------------------------
+// Compute susceptibility based on DCT-coeff histograms:
+// the higher, the "easier" the macroblock is to compress.
+
+#define MAX_ALPHA 255                // 8b of precision for susceptibilities.
+#define ALPHA_SCALE (2 * MAX_ALPHA)  // scaling factor for alpha.
+#define DEFAULT_ALPHA (-1)
+#define IS_BETTER_ALPHA(alpha, best_alpha) ((alpha) > (best_alpha))
+
+static int FinalAlphaValue(int alpha) {
+  alpha = MAX_ALPHA - alpha;
+  return clip(alpha, 0, MAX_ALPHA);
+}
+
+static int GetAlpha(const VP8Histogram* const histo) {
+  // 'alpha' will later be clipped to [0..MAX_ALPHA] range, clamping outer
+  // values which happen to be mostly noise. This leaves the maximum precision
+  // for handling the useful small values which contribute most.
+  const int max_value = histo->max_value;
+  const int last_non_zero = histo->last_non_zero;
+  const int alpha =
+      (max_value > 1) ? ALPHA_SCALE * last_non_zero / max_value : 0;
+  return alpha;
+}
+
+static void InitHistogram(VP8Histogram* const histo) {
+  histo->max_value = 0;
+  histo->last_non_zero = 1;
+}
+
+static void MergeHistograms(const VP8Histogram* const in,
+                            VP8Histogram* const out) {
+  if (in->max_value > out->max_value) {
+    out->max_value = in->max_value;
+  }
+  if (in->last_non_zero > out->last_non_zero) {
+    out->last_non_zero = in->last_non_zero;
+  }
+}
+
+//------------------------------------------------------------------------------
 // Simplified k-Means, to assign Nb segments based on alpha-histogram
 
-static void AssignSegments(VP8Encoder* const enc, const int alphas[256]) {
-  const int nb = enc->segment_hdr_.num_segments_;
+static void AssignSegments(VP8Encoder* const enc,
+                           const int alphas[MAX_ALPHA + 1]) {
+  // 'num_segments_' is previously validated and <= NUM_MB_SEGMENTS, but an
+  // explicit check is needed to avoid spurious warning about 'n + 1' exceeding
+  // array bounds of 'centers' with some compilers (noticed with gcc-4.9).
+  const int nb = (enc->segment_hdr_.num_segments_ < NUM_MB_SEGMENTS) ?
+                 enc->segment_hdr_.num_segments_ : NUM_MB_SEGMENTS;
   int centers[NUM_MB_SEGMENTS];
   int weighted_average = 0;
-  int map[256];
+  int map[MAX_ALPHA + 1];
   int a, n, k;
-  int min_a = 0, max_a = 255, range_a;
+  int min_a = 0, max_a = MAX_ALPHA, range_a;
   // 'int' type is ok for histo, and won't overflow
   int accum[NUM_MB_SEGMENTS], dist_accum[NUM_MB_SEGMENTS];
 
+  assert(nb >= 1);
+  assert(nb <= NUM_MB_SEGMENTS);
+
   // bracket the input
-  for (n = 0; n < 256 && alphas[n] == 0; ++n) {}
+  for (n = 0; n <= MAX_ALPHA && alphas[n] == 0; ++n) {}
   min_a = n;
-  for (n = 255; n > min_a && alphas[n] == 0; --n) {}
+  for (n = MAX_ALPHA; n > min_a && alphas[n] == 0; --n) {}
   max_a = n;
   range_a = max_a - min_a;
 
   // Spread initial centers evenly
-  for (n = 1, k = 0; n < 2 * nb; n += 2) {
-    centers[k++] = min_a + (n * range_a) / (2 * nb);
+  for (k = 0, n = 1; k < nb; ++k, n += 2) {
+    assert(n < 2 * nb);
+    centers[k] = min_a + (n * range_a) / (2 * nb);
   }
 
   for (k = 0; k < MAX_ITERS_K_MEANS; ++k) {     // few iters are enough
@@ -178,7 +182,7 @@ static void AssignSegments(VP8Encoder* const enc, const int alphas[256]) {
     n = 0;    // track the nearest center for current 'a'
     for (a = min_a; a <= max_a; ++a) {
       if (alphas[a]) {
-        while (n < nb - 1 && abs(a - centers[n + 1]) < abs(a - centers[n])) {
+        while (n + 1 < nb && abs(a - centers[n + 1]) < abs(a - centers[n])) {
           n++;
         }
         map[a] = n;
@@ -210,7 +214,7 @@ static void AssignSegments(VP8Encoder* const enc, const int alphas[256]) {
     VP8MBInfo* const mb = &enc->mb_info_[n];
     const int alpha = mb->alpha_;
     mb->segment_ = map[alpha];
-    mb->alpha_ = centers[map[alpha]];     // just for the record.
+    mb->alpha_ = centers[map[alpha]];  // for the record.
   }
 
   if (nb > 1) {
@@ -218,7 +222,6 @@ static void AssignSegments(VP8Encoder* const enc, const int alphas[256]) {
     if (smooth) SmoothSegmentMap(enc);
   }
 
-  SetSegmentProbas(enc);                             // Assign final proba
   SetSegmentAlphas(enc, centers, weighted_average);  // pick some alphas.
 }
 
@@ -227,24 +230,30 @@ static void AssignSegments(VP8Encoder* const enc, const int alphas[256]) {
 // susceptibility and set best modes for this macroblock.
 // Segment assignment is done later.
 
-// Number of modes to inspect for alpha_ evaluation. For high-quality settings,
-// we don't need to test all the possible modes during the analysis phase.
+// Number of modes to inspect for alpha_ evaluation. We don't need to test all
+// the possible modes during the analysis phase: we risk falling into a local
+// optimum, or be subject to boundary effect
 #define MAX_INTRA16_MODE 2
 #define MAX_INTRA4_MODE  2
 #define MAX_UV_MODE      2
 
 static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
-  const int max_mode = (it->enc_->method_ >= 3) ? MAX_INTRA16_MODE : 4;
+  const int max_mode = MAX_INTRA16_MODE;
   int mode;
-  int best_alpha = -1;
+  int best_alpha = DEFAULT_ALPHA;
   int best_mode = 0;
 
   VP8MakeLuma16Preds(it);
   for (mode = 0; mode < max_mode; ++mode) {
-    const int alpha = VP8CollectHistogram(it->yuv_in_ + Y_OFF,
-                                          it->yuv_p_ + VP8I16ModeOffsets[mode],
-                                          0, 16);
-    if (alpha > best_alpha) {
+    VP8Histogram histo;
+    int alpha;
+
+    InitHistogram(&histo);
+    VP8CollectHistogram(it->yuv_in_ + Y_OFF_ENC,
+                        it->yuv_p_ + VP8I16ModeOffsets[mode],
+                        0, 16, &histo);
+    alpha = GetAlpha(&histo);
+    if (IS_BETTER_ALPHA(alpha, best_alpha)) {
       best_alpha = alpha;
       best_mode = mode;
     }
@@ -256,46 +265,62 @@ static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
 static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
                                    int best_alpha) {
   uint8_t modes[16];
-  const int max_mode = (it->enc_->method_ >= 3) ? MAX_INTRA4_MODE : NUM_BMODES;
-  int i4_alpha = 0;
+  const int max_mode = MAX_INTRA4_MODE;
+  int i4_alpha;
+  VP8Histogram total_histo;
+  int cur_histo = 0;
+  InitHistogram(&total_histo);
+
   VP8IteratorStartI4(it);
   do {
     int mode;
-    int best_mode_alpha = -1;
-    const uint8_t* const src = it->yuv_in_ + Y_OFF + VP8Scan[it->i4_];
+    int best_mode_alpha = DEFAULT_ALPHA;
+    VP8Histogram histos[2];
+    const uint8_t* const src = it->yuv_in_ + Y_OFF_ENC + VP8Scan[it->i4_];
 
     VP8MakeIntra4Preds(it);
     for (mode = 0; mode < max_mode; ++mode) {
-      const int alpha = VP8CollectHistogram(src,
-                                            it->yuv_p_ + VP8I4ModeOffsets[mode],
-                                            0, 1);
-      if (alpha > best_mode_alpha) {
+      int alpha;
+
+      InitHistogram(&histos[cur_histo]);
+      VP8CollectHistogram(src, it->yuv_p_ + VP8I4ModeOffsets[mode],
+                          0, 1, &histos[cur_histo]);
+      alpha = GetAlpha(&histos[cur_histo]);
+      if (IS_BETTER_ALPHA(alpha, best_mode_alpha)) {
         best_mode_alpha = alpha;
         modes[it->i4_] = mode;
+        cur_histo ^= 1;   // keep track of best histo so far.
       }
     }
-    i4_alpha += best_mode_alpha;
+    // accumulate best histogram
+    MergeHistograms(&histos[cur_histo ^ 1], &total_histo);
     // Note: we reuse the original samples for predictors
-  } while (VP8IteratorRotateI4(it, it->yuv_in_ + Y_OFF));
+  } while (VP8IteratorRotateI4(it, it->yuv_in_ + Y_OFF_ENC));
 
-  if (i4_alpha > best_alpha) {
+  i4_alpha = GetAlpha(&total_histo);
+  if (IS_BETTER_ALPHA(i4_alpha, best_alpha)) {
     VP8SetIntra4Mode(it, modes);
-    best_alpha = ClipAlpha(i4_alpha);
+    best_alpha = i4_alpha;
   }
   return best_alpha;
 }
 
 static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
-  int best_alpha = -1;
+  int best_alpha = DEFAULT_ALPHA;
   int best_mode = 0;
-  const int max_mode = (it->enc_->method_ >= 3) ? MAX_UV_MODE : 4;
+  const int max_mode = MAX_UV_MODE;
   int mode;
+
   VP8MakeChroma8Preds(it);
   for (mode = 0; mode < max_mode; ++mode) {
-    const int alpha = VP8CollectHistogram(it->yuv_in_ + U_OFF,
-                                          it->yuv_p_ + VP8UVModeOffsets[mode],
-                                          16, 16 + 4 + 4);
-    if (alpha > best_alpha) {
+    VP8Histogram histo;
+    int alpha;
+    InitHistogram(&histo);
+    VP8CollectHistogram(it->yuv_in_ + U_OFF_ENC,
+                        it->yuv_p_ + VP8UVModeOffsets[mode],
+                        16, 16 + 4 + 4, &histo);
+    alpha = GetAlpha(&histo);
+    if (IS_BETTER_ALPHA(alpha, best_alpha)) {
       best_alpha = alpha;
       best_mode = mode;
     }
@@ -305,7 +330,8 @@ static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
 }
 
 static void MBAnalyze(VP8EncIterator* const it,
-                      int alphas[256], int* const uv_alpha) {
+                      int alphas[MAX_ALPHA + 1],
+                      int* const alpha, int* const uv_alpha) {
   const VP8Encoder* const enc = it->enc_;
   int best_alpha, best_uv_alpha;
 
@@ -314,7 +340,7 @@ static void MBAnalyze(VP8EncIterator* const it,
   VP8SetSegment(it, 0);      // default segment, spec-wise.
 
   best_alpha = MBAnalyzeBestIntra16Mode(it);
-  if (enc->method_ != 3) {
+  if (enc->method_ >= 5) {
     // We go and make a fast decision for intra4/intra16.
     // It's usually not a good and definitive pick, but helps seeding the stats
     // about level bit-cost.
@@ -324,10 +350,22 @@ static void MBAnalyze(VP8EncIterator* const it,
   best_uv_alpha = MBAnalyzeBestUVMode(it);
 
   // Final susceptibility mix
-  best_alpha = (best_alpha + best_uv_alpha + 1) / 2;
+  best_alpha = (3 * best_alpha + best_uv_alpha + 2) >> 2;
+  best_alpha = FinalAlphaValue(best_alpha);
   alphas[best_alpha]++;
+  it->mb_->alpha_ = best_alpha;   // for later remapping.
+
+  // Accumulate for later complexity analysis.
+  *alpha += best_alpha;   // mixed susceptibility (not just luma)
   *uv_alpha += best_uv_alpha;
-  it->mb_->alpha_ = best_alpha;   // Informative only.
+}
+
+static void DefaultMBInfo(VP8MBInfo* const mb) {
+  mb->type_ = 1;     // I16x16
+  mb->uv_mode_ = 0;
+  mb->skip_ = 0;     // not skipped
+  mb->segment_ = 0;  // default segment
+  mb->alpha_ = 0;
 }
 
 //------------------------------------------------------------------------------
@@ -340,25 +378,124 @@ static void MBAnalyze(VP8EncIterator* const it,
 // and decide intra4/intra16, but that's usually almost always a bad choice at
 // this stage.
 
-int VP8EncAnalyze(VP8Encoder* const enc) {
-  int ok = 1;
-  int alphas[256] = { 0 };
-  VP8EncIterator it;
-
-  VP8IteratorInit(enc, &it);
+static void ResetAllMBInfo(VP8Encoder* const enc) {
+  int n;
+  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
+    DefaultMBInfo(&enc->mb_info_[n]);
+  }
+  // Default susceptibilities.
+  enc->dqm_[0].alpha_ = 0;
+  enc->dqm_[0].beta_ = 0;
+  // Note: we can't compute this alpha_ / uv_alpha_ -> set to default value.
+  enc->alpha_ = 0;
   enc->uv_alpha_ = 0;
-  do {
-    VP8IteratorImport(&it);
-    MBAnalyze(&it, alphas, &enc->uv_alpha_);
-    ok = VP8IteratorProgress(&it, 20);
-    // Let's pretend we have perfect lossless reconstruction.
-  } while (ok && VP8IteratorNext(&it, it.yuv_in_));
-  enc->uv_alpha_ /= enc->mb_w_ * enc->mb_h_;
-  if (ok) AssignSegments(enc, alphas);
+  WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
+}
+
+// struct used to collect job result
+typedef struct {
+  WebPWorker worker;
+  int alphas[MAX_ALPHA + 1];
+  int alpha, uv_alpha;
+  VP8EncIterator it;
+  int delta_progress;
+} SegmentJob;
 
+// main work call
+static int DoSegmentsJob(SegmentJob* const job, VP8EncIterator* const it) {
+  int ok = 1;
+  if (!VP8IteratorIsDone(it)) {
+    uint8_t tmp[32 + WEBP_ALIGN_CST];
+    uint8_t* const scratch = (uint8_t*)WEBP_ALIGN(tmp);
+    do {
+      // Let's pretend we have perfect lossless reconstruction.
+      VP8IteratorImport(it, scratch);
+      MBAnalyze(it, job->alphas, &job->alpha, &job->uv_alpha);
+      ok = VP8IteratorProgress(it, job->delta_progress);
+    } while (ok && VP8IteratorNext(it));
+  }
   return ok;
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
+static void MergeJobs(const SegmentJob* const src, SegmentJob* const dst) {
+  int i;
+  for (i = 0; i <= MAX_ALPHA; ++i) dst->alphas[i] += src->alphas[i];
+  dst->alpha += src->alpha;
+  dst->uv_alpha += src->uv_alpha;
+}
+
+// initialize the job struct with some TODOs
+static void InitSegmentJob(VP8Encoder* const enc, SegmentJob* const job,
+                           int start_row, int end_row) {
+  WebPGetWorkerInterface()->Init(&job->worker);
+  job->worker.data1 = job;
+  job->worker.data2 = &job->it;
+  job->worker.hook = (WebPWorkerHook)DoSegmentsJob;
+  VP8IteratorInit(enc, &job->it);
+  VP8IteratorSetRow(&job->it, start_row);
+  VP8IteratorSetCountDown(&job->it, (end_row - start_row) * enc->mb_w_);
+  memset(job->alphas, 0, sizeof(job->alphas));
+  job->alpha = 0;
+  job->uv_alpha = 0;
+  // only one of both jobs can record the progress, since we don't
+  // expect the user's hook to be multi-thread safe
+  job->delta_progress = (start_row == 0) ? 20 : 0;
+}
+
+// main entry point
+int VP8EncAnalyze(VP8Encoder* const enc) {
+  int ok = 1;
+  const int do_segments =
+      enc->config_->emulate_jpeg_size ||   // We need the complexity evaluation.
+      (enc->segment_hdr_.num_segments_ > 1) ||
+      (enc->method_ == 0);  // for method 0, we need preds_[] to be filled.
+  if (do_segments) {
+    const int last_row = enc->mb_h_;
+    // We give a little more than a half work to the main thread.
+    const int split_row = (9 * last_row + 15) >> 4;
+    const int total_mb = last_row * enc->mb_w_;
+#ifdef WEBP_USE_THREAD
+    const int kMinSplitRow = 2;  // minimal rows needed for mt to be worth it
+    const int do_mt = (enc->thread_level_ > 0) && (split_row >= kMinSplitRow);
+#else
+    const int do_mt = 0;
 #endif
+    const WebPWorkerInterface* const worker_interface =
+        WebPGetWorkerInterface();
+    SegmentJob main_job;
+    if (do_mt) {
+      SegmentJob side_job;
+      // Note the use of '&' instead of '&&' because we must call the functions
+      // no matter what.
+      InitSegmentJob(enc, &main_job, 0, split_row);
+      InitSegmentJob(enc, &side_job, split_row, last_row);
+      // we don't need to call Reset() on main_job.worker, since we're calling
+      // WebPWorkerExecute() on it
+      ok &= worker_interface->Reset(&side_job.worker);
+      // launch the two jobs in parallel
+      if (ok) {
+        worker_interface->Launch(&side_job.worker);
+        worker_interface->Execute(&main_job.worker);
+        ok &= worker_interface->Sync(&side_job.worker);
+        ok &= worker_interface->Sync(&main_job.worker);
+      }
+      worker_interface->End(&side_job.worker);
+      if (ok) MergeJobs(&side_job, &main_job);  // merge results together
+    } else {
+      // Even for single-thread case, we use the generic Worker tools.
+      InitSegmentJob(enc, &main_job, 0, last_row);
+      worker_interface->Execute(&main_job.worker);
+      ok &= worker_interface->Sync(&main_job.worker);
+    }
+    worker_interface->End(&main_job.worker);
+    if (ok) {
+      enc->alpha_ = main_job.alpha / total_mb;
+      enc->uv_alpha_ = main_job.uv_alpha / total_mb;
+      AssignSegments(enc, main_job.alphas);
+    }
+  } else {   // Use only one default segment.
+    ResetAllMBInfo(enc);
+  }
+  return ok;
+}
+
diff --git a/drivers/webp/enc/backward_references.c b/drivers/webp/enc/backward_references.c
index b8c8ece806..049125e521 100644
--- a/drivers/webp/enc/backward_references.c
+++ b/drivers/webp/enc/backward_references.c
@@ -1,8 +1,10 @@
 // Copyright 2012 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Author: Jyrki Alakuijala (jyrki@google.com)
@@ -10,7 +12,6 @@
 
 #include <assert.h>
 #include <math.h>
-#include <stdio.h>
 
 #include "./backward_references.h"
 #include "./histogram.h"
@@ -20,9 +21,9 @@
 
 #define VALUES_IN_BYTE 256
 
-#define HASH_BITS 18
-#define HASH_SIZE (1 << HASH_BITS)
-#define HASH_MULTIPLIER (0xc6a4a7935bd1e995ULL)
+#define MIN_BLOCK_SIZE 256  // minimum block size for backward references
+
+#define MAX_ENTROPY    (1e30f)
 
 // 1M window (4M bytes) minus 120 special codes for short distances.
 #define WINDOW_SIZE ((1 << 20) - 120)
@@ -31,14 +32,6 @@
 #define MIN_LENGTH 2
 #define MAX_LENGTH 4096
 
-typedef struct {
-  // Stores the most recently added position with the given hash value.
-  int32_t hash_to_first_index_[HASH_SIZE];
-  // chain_[pos] stores the previous position with the same hash value
-  // for every pixel in the image.
-  int32_t* chain_;
-} HashChain;
-
 // -----------------------------------------------------------------------------
 
 static const uint8_t plane_to_code_lut[128] = {
@@ -65,145 +58,275 @@ static int DistanceToPlaneCode(int xsize, int dist) {
 
 static WEBP_INLINE int FindMatchLength(const uint32_t* const array1,
                                        const uint32_t* const array2,
-                                       const int max_limit) {
+                                       int best_len_match,
+                                       int max_limit) {
+#if !defined(__x86_64__)
+  // TODO(vrabaud): Compare on other architectures.
   int match_len = 0;
+  // Before 'expensive' linear match, check if the two arrays match at the
+  // current best length index.
+  if (array1[best_len_match] != array2[best_len_match]) return 0;
   while (match_len < max_limit && array1[match_len] == array2[match_len]) {
     ++match_len;
   }
   return match_len;
+#else
+  const uint32_t* array1_32 = array1;
+  const uint32_t* array2_32 = array2;
+  // max value is aligned to (uint64_t*) array1
+  const uint32_t* const array1_32_max = array1 + (max_limit & ~1);
+
+  // Before 'expensive' linear match, check if the two arrays match at the
+  // current best length index.
+  if (array1[best_len_match] != array2[best_len_match]) return 0;
+
+  // TODO(vrabaud): add __predict_true on bound checking?
+  while (array1_32 < array1_32_max) {
+    if (*(uint64_t*)array1_32 == *(uint64_t*)array2_32) {
+      array1_32 += 2;
+      array2_32 += 2;
+    } else {
+      // if the uint32_t pointed to are the same, then the following ones have
+      // to be different
+      return (array1_32 - array1) + (*array1_32 == *array2_32);
+    }
+  }
+
+  // Deal with the potential last uint32_t.
+  if ((max_limit & 1) && (*array1_32 != *array2_32)) return max_limit - 1;
+  return max_limit;
+#endif
 }
 
 // -----------------------------------------------------------------------------
 //  VP8LBackwardRefs
 
-void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs) {
-  if (refs != NULL) {
-    refs->refs = NULL;
-    refs->size = 0;
-    refs->max_size = 0;
+struct PixOrCopyBlock {
+  PixOrCopyBlock* next_;   // next block (or NULL)
+  PixOrCopy* start_;       // data start
+  int size_;               // currently used size
+};
+
+static void ClearBackwardRefs(VP8LBackwardRefs* const refs) {
+  assert(refs != NULL);
+  if (refs->tail_ != NULL) {
+    *refs->tail_ = refs->free_blocks_;  // recycle all blocks at once
   }
+  refs->free_blocks_ = refs->refs_;
+  refs->tail_ = &refs->refs_;
+  refs->last_block_ = NULL;
+  refs->refs_ = NULL;
 }
 
-void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs) {
-  if (refs != NULL) {
-    free(refs->refs);
-    VP8LInitBackwardRefs(refs);
+void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs) {
+  assert(refs != NULL);
+  ClearBackwardRefs(refs);
+  while (refs->free_blocks_ != NULL) {
+    PixOrCopyBlock* const next = refs->free_blocks_->next_;
+    WebPSafeFree(refs->free_blocks_);
+    refs->free_blocks_ = next;
   }
 }
 
-int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size) {
+void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size) {
   assert(refs != NULL);
-  refs->size = 0;
-  refs->max_size = 0;
-  refs->refs = (PixOrCopy*)WebPSafeMalloc((uint64_t)max_size,
-                                          sizeof(*refs->refs));
-  if (refs->refs == NULL) return 0;
-  refs->max_size = max_size;
+  memset(refs, 0, sizeof(*refs));
+  refs->tail_ = &refs->refs_;
+  refs->block_size_ =
+      (block_size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : block_size;
+}
+
+VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs) {
+  VP8LRefsCursor c;
+  c.cur_block_ = refs->refs_;
+  if (refs->refs_ != NULL) {
+    c.cur_pos = c.cur_block_->start_;
+    c.last_pos_ = c.cur_pos + c.cur_block_->size_;
+  } else {
+    c.cur_pos = NULL;
+    c.last_pos_ = NULL;
+  }
+  return c;
+}
+
+void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c) {
+  PixOrCopyBlock* const b = c->cur_block_->next_;
+  c->cur_pos = (b == NULL) ? NULL : b->start_;
+  c->last_pos_ = (b == NULL) ? NULL : b->start_ + b->size_;
+  c->cur_block_ = b;
+}
+
+// Create a new block, either from the free list or allocated
+static PixOrCopyBlock* BackwardRefsNewBlock(VP8LBackwardRefs* const refs) {
+  PixOrCopyBlock* b = refs->free_blocks_;
+  if (b == NULL) {   // allocate new memory chunk
+    const size_t total_size =
+        sizeof(*b) + refs->block_size_ * sizeof(*b->start_);
+    b = (PixOrCopyBlock*)WebPSafeMalloc(1ULL, total_size);
+    if (b == NULL) {
+      refs->error_ |= 1;
+      return NULL;
+    }
+    b->start_ = (PixOrCopy*)((uint8_t*)b + sizeof(*b));  // not always aligned
+  } else {  // recycle from free-list
+    refs->free_blocks_ = b->next_;
+  }
+  *refs->tail_ = b;
+  refs->tail_ = &b->next_;
+  refs->last_block_ = b;
+  b->next_ = NULL;
+  b->size_ = 0;
+  return b;
+}
+
+static WEBP_INLINE void BackwardRefsCursorAdd(VP8LBackwardRefs* const refs,
+                                              const PixOrCopy v) {
+  PixOrCopyBlock* b = refs->last_block_;
+  if (b == NULL || b->size_ == refs->block_size_) {
+    b = BackwardRefsNewBlock(refs);
+    if (b == NULL) return;   // refs->error_ is set
+  }
+  b->start_[b->size_++] = v;
+}
+
+int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
+                         VP8LBackwardRefs* const dst) {
+  const PixOrCopyBlock* b = src->refs_;
+  ClearBackwardRefs(dst);
+  assert(src->block_size_ == dst->block_size_);
+  while (b != NULL) {
+    PixOrCopyBlock* const new_b = BackwardRefsNewBlock(dst);
+    if (new_b == NULL) return 0;   // dst->error_ is set
+    memcpy(new_b->start_, b->start_, b->size_ * sizeof(*b->start_));
+    new_b->size_ = b->size_;
+    b = b->next_;
+  }
   return 1;
 }
 
 // -----------------------------------------------------------------------------
 // Hash chains
 
-static WEBP_INLINE uint64_t GetPixPairHash64(const uint32_t* const argb) {
-  uint64_t key = ((uint64_t)(argb[1]) << 32) | argb[0];
-  key = (key * HASH_MULTIPLIER) >> (64 - HASH_BITS);
-  return key;
-}
-
-static int HashChainInit(HashChain* const p, int size) {
+// initialize as empty
+static void HashChainReset(VP8LHashChain* const p) {
   int i;
-  p->chain_ = (int*)WebPSafeMalloc((uint64_t)size, sizeof(*p->chain_));
-  if (p->chain_ == NULL) {
-    return 0;
-  }
-  for (i = 0; i < size; ++i) {
+  assert(p != NULL);
+  for (i = 0; i < p->size_; ++i) {
     p->chain_[i] = -1;
   }
   for (i = 0; i < HASH_SIZE; ++i) {
     p->hash_to_first_index_[i] = -1;
   }
+}
+
+int VP8LHashChainInit(VP8LHashChain* const p, int size) {
+  assert(p->size_ == 0);
+  assert(p->chain_ == NULL);
+  assert(size > 0);
+  p->chain_ = (int*)WebPSafeMalloc(size, sizeof(*p->chain_));
+  if (p->chain_ == NULL) return 0;
+  p->size_ = size;
+  HashChainReset(p);
   return 1;
 }
 
-static void HashChainDelete(HashChain* const p) {
-  if (p != NULL) {
-    free(p->chain_);
-    free(p);
-  }
+void VP8LHashChainClear(VP8LHashChain* const p) {
+  assert(p != NULL);
+  WebPSafeFree(p->chain_);
+  p->size_ = 0;
+  p->chain_ = NULL;
+}
+
+// -----------------------------------------------------------------------------
+
+#define HASH_MULTIPLIER_HI (0xc6a4a793U)
+#define HASH_MULTIPLIER_LO (0x5bd1e996U)
+
+static WEBP_INLINE uint32_t GetPixPairHash64(const uint32_t* const argb) {
+  uint32_t key;
+  key  = argb[1] * HASH_MULTIPLIER_HI;
+  key += argb[0] * HASH_MULTIPLIER_LO;
+  key = key >> (32 - HASH_BITS);
+  return key;
 }
 
 // Insertion of two pixels at a time.
-static void HashChainInsert(HashChain* const p,
+static void HashChainInsert(VP8LHashChain* const p,
                             const uint32_t* const argb, int pos) {
-  const uint64_t hash_code = GetPixPairHash64(argb);
+  const uint32_t hash_code = GetPixPairHash64(argb);
   p->chain_[pos] = p->hash_to_first_index_[hash_code];
   p->hash_to_first_index_[hash_code] = pos;
 }
 
-static int HashChainFindCopy(const HashChain* const p,
-                             int quality, int index, int xsize,
-                             const uint32_t* const argb, int maxlen,
+// Returns the maximum number of hash chain lookups to do for a
+// given compression quality. Return value in range [6, 86].
+static int GetMaxItersForQuality(int quality, int low_effort) {
+  return (low_effort ? 6 : 8) + (quality * quality) / 128;
+}
+
+static int GetWindowSizeForHashChain(int quality, int xsize) {
+  const int max_window_size = (quality > 75) ? WINDOW_SIZE
+                            : (quality > 50) ? (xsize << 8)
+                            : (quality > 25) ? (xsize << 6)
+                            : (xsize << 4);
+  assert(xsize > 0);
+  return (max_window_size > WINDOW_SIZE) ? WINDOW_SIZE : max_window_size;
+}
+
+static WEBP_INLINE int MaxFindCopyLength(int len) {
+  return (len < MAX_LENGTH) ? len : MAX_LENGTH;
+}
+
+static void HashChainFindOffset(const VP8LHashChain* const p, int base_position,
+                                const uint32_t* const argb, int len,
+                                int window_size, int* const distance_ptr) {
+  const uint32_t* const argb_start = argb + base_position;
+  const int min_pos =
+      (base_position > window_size) ? base_position - window_size : 0;
+  int pos;
+  assert(len <= MAX_LENGTH);
+  for (pos = p->hash_to_first_index_[GetPixPairHash64(argb_start)];
+       pos >= min_pos;
+       pos = p->chain_[pos]) {
+    const int curr_length =
+        FindMatchLength(argb + pos, argb_start, len - 1, len);
+    if (curr_length == len) break;
+  }
+  *distance_ptr = base_position - pos;
+}
+
+static int HashChainFindCopy(const VP8LHashChain* const p,
+                             int base_position,
+                             const uint32_t* const argb, int max_len,
+                             int window_size, int iter_max,
                              int* const distance_ptr,
                              int* const length_ptr) {
-  const uint64_t hash_code = GetPixPairHash64(&argb[index]);
-  int prev_length = 0;
-  int64_t best_val = 0;
+  const uint32_t* const argb_start = argb + base_position;
+  int iter = iter_max;
   int best_length = 0;
   int best_distance = 0;
-  const uint32_t* const argb_start = argb + index;
-  const int iter_min_mult = (quality < 50) ? 2 : (quality < 75) ? 4 : 8;
-  const int iter_min = -quality * iter_min_mult;
-  int iter_cnt = 10 + (quality >> 1);
-  const int min_pos = (index > WINDOW_SIZE) ? index - WINDOW_SIZE : 0;
+  const int min_pos =
+      (base_position > window_size) ? base_position - window_size : 0;
   int pos;
-
-  assert(xsize > 0);
-  for (pos = p->hash_to_first_index_[hash_code];
+  int length_max = 256;
+  if (max_len < length_max) {
+    length_max = max_len;
+  }
+  for (pos = p->hash_to_first_index_[GetPixPairHash64(argb_start)];
        pos >= min_pos;
        pos = p->chain_[pos]) {
-    int64_t val;
     int curr_length;
-    if (iter_cnt < 0) {
-      if (iter_cnt < iter_min || best_val >= 0xff0000) {
-        break;
-      }
-    }
-    --iter_cnt;
-    if (best_length != 0 &&
-        argb[pos + best_length - 1] != argb_start[best_length - 1]) {
-      continue;
-    }
-    curr_length = FindMatchLength(argb + pos, argb_start, maxlen);
-    if (curr_length < prev_length) {
-      continue;
+    int distance;
+    if (--iter < 0) {
+      break;
     }
-    val = 65536 * curr_length;
-    // Favoring 2d locality here gives savings for certain images.
-    if (index - pos < 9 * xsize) {
-      const int y = (index - pos) / xsize;
-      int x = (index - pos) % xsize;
-      if (x > xsize / 2) {
-        x = xsize - x;
-      }
-      if (x <= 7 && x >= -8) {
-        val -= y * y + x * x;
-      } else {
-        val -= 9 * 9 + 9 * 9;
-      }
-    } else {
-      val -= 9 * 9 + 9 * 9;
-    }
-    if (best_val < val) {
-      prev_length = curr_length;
-      best_val = val;
+
+    curr_length = FindMatchLength(argb + pos, argb_start, best_length, max_len);
+    if (best_length < curr_length) {
+      distance = base_position - pos;
       best_length = curr_length;
-      best_distance = index - pos;
-      if (curr_length >= MAX_LENGTH) {
-        break;
-      }
-      if ((best_distance == 1 || best_distance == xsize) &&
-          best_length >= 128) {
+      best_distance = distance;
+      if (curr_length >= length_max) {
         break;
       }
     }
@@ -213,140 +336,153 @@ static int HashChainFindCopy(const HashChain* const p,
   return (best_length >= MIN_LENGTH);
 }
 
-static WEBP_INLINE void PushBackCopy(VP8LBackwardRefs* const refs, int length) {
-  int size = refs->size;
-  while (length >= MAX_LENGTH) {
-    refs->refs[size++] = PixOrCopyCreateCopy(1, MAX_LENGTH);
-    length -= MAX_LENGTH;
-  }
-  if (length > 0) {
-    refs->refs[size++] = PixOrCopyCreateCopy(1, length);
+static WEBP_INLINE void AddSingleLiteral(uint32_t pixel, int use_color_cache,
+                                         VP8LColorCache* const hashers,
+                                         VP8LBackwardRefs* const refs) {
+  PixOrCopy v;
+  if (use_color_cache) {
+    const uint32_t key = VP8LColorCacheGetIndex(hashers, pixel);
+    if (VP8LColorCacheLookup(hashers, key) == pixel) {
+      v = PixOrCopyCreateCacheIdx(key);
+    } else {
+      v = PixOrCopyCreateLiteral(pixel);
+      VP8LColorCacheSet(hashers, key, pixel);
+    }
+  } else {
+    v = PixOrCopyCreateLiteral(pixel);
   }
-  refs->size = size;
+  BackwardRefsCursorAdd(refs, v);
 }
 
-static void BackwardReferencesRle(int xsize, int ysize,
-                                  const uint32_t* const argb,
-                                  VP8LBackwardRefs* const refs) {
+static int BackwardReferencesRle(int xsize, int ysize,
+                                 const uint32_t* const argb,
+                                 int cache_bits, VP8LBackwardRefs* const refs) {
   const int pix_count = xsize * ysize;
-  int match_len = 0;
-  int i;
-  refs->size = 0;
-  PushBackCopy(refs, match_len);    // i=0 case
-  refs->refs[refs->size++] = PixOrCopyCreateLiteral(argb[0]);
-  for (i = 1; i < pix_count; ++i) {
-    if (argb[i] == argb[i - 1]) {
-      ++match_len;
+  int i, k;
+  const int use_color_cache = (cache_bits > 0);
+  VP8LColorCache hashers;
+
+  if (use_color_cache && !VP8LColorCacheInit(&hashers, cache_bits)) {
+    return 0;
+  }
+  ClearBackwardRefs(refs);
+  // Add first pixel as literal.
+  AddSingleLiteral(argb[0], use_color_cache, &hashers, refs);
+  i = 1;
+  while (i < pix_count) {
+    const int max_len = MaxFindCopyLength(pix_count - i);
+    const int kMinLength = 4;
+    const int rle_len = FindMatchLength(argb + i, argb + i - 1, 0, max_len);
+    const int prev_row_len = (i < xsize) ? 0 :
+        FindMatchLength(argb + i, argb + i - xsize, 0, max_len);
+    if (rle_len >= prev_row_len && rle_len >= kMinLength) {
+      BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, rle_len));
+      // We don't need to update the color cache here since it is always the
+      // same pixel being copied, and that does not change the color cache
+      // state.
+      i += rle_len;
+    } else if (prev_row_len >= kMinLength) {
+      BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(xsize, prev_row_len));
+      if (use_color_cache) {
+        for (k = 0; k < prev_row_len; ++k) {
+          VP8LColorCacheInsert(&hashers, argb[i + k]);
+        }
+      }
+      i += prev_row_len;
     } else {
-      PushBackCopy(refs, match_len);
-      match_len = 0;
-      refs->refs[refs->size++] = PixOrCopyCreateLiteral(argb[i]);
+      AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
+      i++;
     }
   }
-  PushBackCopy(refs, match_len);
+  if (use_color_cache) VP8LColorCacheClear(&hashers);
+  return !refs->error_;
 }
 
-static int BackwardReferencesHashChain(int xsize, int ysize,
-                                       const uint32_t* const argb,
-                                       int cache_bits, int quality,
-                                       VP8LBackwardRefs* const refs) {
+static int BackwardReferencesLz77(int xsize, int ysize,
+                                  const uint32_t* const argb, int cache_bits,
+                                  int quality, int low_effort,
+                                  VP8LHashChain* const hash_chain,
+                                  VP8LBackwardRefs* const refs) {
   int i;
   int ok = 0;
   int cc_init = 0;
   const int use_color_cache = (cache_bits > 0);
   const int pix_count = xsize * ysize;
-  HashChain* const hash_chain = (HashChain*)malloc(sizeof(*hash_chain));
   VP8LColorCache hashers;
+  int iter_max = GetMaxItersForQuality(quality, low_effort);
+  const int window_size = GetWindowSizeForHashChain(quality, xsize);
+  int min_matches = 32;
 
-  if (hash_chain == NULL) return 0;
   if (use_color_cache) {
     cc_init = VP8LColorCacheInit(&hashers, cache_bits);
     if (!cc_init) goto Error;
   }
-
-  if (!HashChainInit(hash_chain, pix_count)) goto Error;
-
-  refs->size = 0;
-  for (i = 0; i < pix_count; ) {
+  ClearBackwardRefs(refs);
+  HashChainReset(hash_chain);
+  for (i = 0; i < pix_count - 2; ) {
     // Alternative#1: Code the pixels starting at 'i' using backward reference.
     int offset = 0;
     int len = 0;
-    if (i < pix_count - 1) {  // FindCopy(i,..) reads pixels at [i] and [i + 1].
-      int maxlen = pix_count - i;
-      if (maxlen > MAX_LENGTH) {
-        maxlen = MAX_LENGTH;
-      }
-      HashChainFindCopy(hash_chain, quality, i, xsize, argb, maxlen,
-                        &offset, &len);
-    }
-    if (len >= MIN_LENGTH) {
-      // Alternative#2: Insert the pixel at 'i' as literal, and code the
-      // pixels starting at 'i + 1' using backward reference.
+    const int max_len = MaxFindCopyLength(pix_count - i);
+    HashChainFindCopy(hash_chain, i, argb, max_len, window_size,
+                      iter_max, &offset, &len);
+    if (len > MIN_LENGTH || (len == MIN_LENGTH && offset <= 512)) {
       int offset2 = 0;
       int len2 = 0;
       int k;
+      min_matches = 8;
       HashChainInsert(hash_chain, &argb[i], i);
-      if (i < pix_count - 2) {  // FindCopy(i+1,..) reads [i + 1] and [i + 2].
-        int maxlen = pix_count - (i + 1);
-        if (maxlen > MAX_LENGTH) {
-          maxlen = MAX_LENGTH;
-        }
-        HashChainFindCopy(hash_chain, quality,
-                          i + 1, xsize, argb, maxlen, &offset2, &len2);
+      if ((len < (max_len >> 2)) && !low_effort) {
+        // Evaluate Alternative#2: Insert the pixel at 'i' as literal, and code
+        // the pixels starting at 'i + 1' using backward reference.
+        HashChainFindCopy(hash_chain, i + 1, argb, max_len - 1,
+                          window_size, iter_max, &offset2,
+                          &len2);
         if (len2 > len + 1) {
-          const uint32_t pixel = argb[i];
-          // Alternative#2 is a better match. So push pixel at 'i' as literal.
-          if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
-            const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
-            refs->refs[refs->size] = PixOrCopyCreateCacheIdx(ix);
-          } else {
-            refs->refs[refs->size] = PixOrCopyCreateLiteral(pixel);
-          }
-          ++refs->size;
-          if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
+          AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
           i++;  // Backward reference to be done for next pixel.
           len = len2;
           offset = offset2;
         }
       }
-      if (len >= MAX_LENGTH) {
-        len = MAX_LENGTH - 1;
-      }
-      refs->refs[refs->size++] = PixOrCopyCreateCopy(offset, len);
+      BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(offset, len));
       if (use_color_cache) {
         for (k = 0; k < len; ++k) {
           VP8LColorCacheInsert(&hashers, argb[i + k]);
         }
       }
       // Add to the hash_chain (but cannot add the last pixel).
-      {
+      if (offset >= 3 && offset != xsize) {
         const int last = (len < pix_count - 1 - i) ? len : pix_count - 1 - i;
-        for (k = 1; k < last; ++k) {
+        for (k = 2; k < last - 8; k += 2) {
+          HashChainInsert(hash_chain, &argb[i + k], i + k);
+        }
+        for (; k < last; ++k) {
           HashChainInsert(hash_chain, &argb[i + k], i + k);
         }
       }
       i += len;
     } else {
-      const uint32_t pixel = argb[i];
-      if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
-        // push pixel as a PixOrCopyCreateCacheIdx pixel
-        const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
-        refs->refs[refs->size] = PixOrCopyCreateCacheIdx(ix);
-      } else {
-        refs->refs[refs->size] = PixOrCopyCreateLiteral(pixel);
-      }
-      ++refs->size;
-      if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
-      if (i + 1 < pix_count) {
+      AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
+      HashChainInsert(hash_chain, &argb[i], i);
+      ++i;
+      --min_matches;
+      if (min_matches <= 0) {
+        AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
         HashChainInsert(hash_chain, &argb[i], i);
+        ++i;
       }
-      ++i;
     }
   }
-  ok = 1;
-Error:
+  while (i < pix_count) {
+    // Handle the last pixel(s).
+    AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
+    ++i;
+  }
+
+  ok = !refs->error_;
+ Error:
   if (cc_init) VP8LColorCacheClear(&hashers);
-  HashChainDelete(hash_chain);
   return ok;
 }
 
@@ -355,18 +491,19 @@ Error:
 typedef struct {
   double alpha_[VALUES_IN_BYTE];
   double red_[VALUES_IN_BYTE];
-  double literal_[PIX_OR_COPY_CODES_MAX];
   double blue_[VALUES_IN_BYTE];
   double distance_[NUM_DISTANCE_CODES];
+  double* literal_;
 } CostModel;
 
 static int BackwardReferencesTraceBackwards(
-    int xsize, int ysize, int recursive_cost_model,
-    const uint32_t* const argb, int cache_bits, VP8LBackwardRefs* const refs);
+    int xsize, int ysize, const uint32_t* const argb, int quality,
+    int cache_bits, VP8LHashChain* const hash_chain,
+    VP8LBackwardRefs* const refs);
 
 static void ConvertPopulationCountTableToBitEstimates(
-    int num_symbols, const int population_counts[], double output[]) {
-  int sum = 0;
+    int num_symbols, const uint32_t population_counts[], double output[]) {
+  uint32_t sum = 0;
   int nonzeros = 0;
   int i;
   for (i = 0; i < num_symbols; ++i) {
@@ -385,42 +522,29 @@ static void ConvertPopulationCountTableToBitEstimates(
   }
 }
 
-static int CostModelBuild(CostModel* const m, int xsize, int ysize,
-                          int recursion_level, const uint32_t* const argb,
-                          int cache_bits) {
+static int CostModelBuild(CostModel* const m, int cache_bits,
+                          VP8LBackwardRefs* const refs) {
   int ok = 0;
-  VP8LHistogram histo;
-  VP8LBackwardRefs refs;
-  const int quality = 100;
+  VP8LHistogram* const histo = VP8LAllocateHistogram(cache_bits);
+  if (histo == NULL) goto Error;
 
-  if (!VP8LBackwardRefsAlloc(&refs, xsize * ysize)) goto Error;
+  VP8LHistogramCreate(histo, refs, cache_bits);
 
-  if (recursion_level > 0) {
-    if (!BackwardReferencesTraceBackwards(xsize, ysize, recursion_level - 1,
-                                          argb, cache_bits, &refs)) {
-      goto Error;
-    }
-  } else {
-    if (!BackwardReferencesHashChain(xsize, ysize, argb, cache_bits, quality,
-                                     &refs)) {
-      goto Error;
-    }
-  }
-  VP8LHistogramCreate(&histo, &refs, cache_bits);
   ConvertPopulationCountTableToBitEstimates(
-      VP8LHistogramNumCodes(&histo), histo.literal_, m->literal_);
+      VP8LHistogramNumCodes(histo->palette_code_bits_),
+      histo->literal_, m->literal_);
   ConvertPopulationCountTableToBitEstimates(
-      VALUES_IN_BYTE, histo.red_, m->red_);
+      VALUES_IN_BYTE, histo->red_, m->red_);
   ConvertPopulationCountTableToBitEstimates(
-      VALUES_IN_BYTE, histo.blue_, m->blue_);
+      VALUES_IN_BYTE, histo->blue_, m->blue_);
   ConvertPopulationCountTableToBitEstimates(
-      VALUES_IN_BYTE, histo.alpha_, m->alpha_);
+      VALUES_IN_BYTE, histo->alpha_, m->alpha_);
   ConvertPopulationCountTableToBitEstimates(
-      NUM_DISTANCE_CODES, histo.distance_, m->distance_);
+      NUM_DISTANCE_CODES, histo->distance_, m->distance_);
   ok = 1;
 
  Error:
-  VP8LClearBackwardRefs(&refs);
+  VP8LFreeHistogram(histo);
   return ok;
 }
 
@@ -438,203 +562,211 @@ static WEBP_INLINE double GetCacheCost(const CostModel* const m, uint32_t idx) {
 
 static WEBP_INLINE double GetLengthCost(const CostModel* const m,
                                         uint32_t length) {
-  int code, extra_bits_count, extra_bits_value;
-  PrefixEncode(length, &code, &extra_bits_count, &extra_bits_value);
-  return m->literal_[VALUES_IN_BYTE + code] + extra_bits_count;
+  int code, extra_bits;
+  VP8LPrefixEncodeBits(length, &code, &extra_bits);
+  return m->literal_[VALUES_IN_BYTE + code] + extra_bits;
 }
 
 static WEBP_INLINE double GetDistanceCost(const CostModel* const m,
                                           uint32_t distance) {
-  int code, extra_bits_count, extra_bits_value;
-  PrefixEncode(distance, &code, &extra_bits_count, &extra_bits_value);
-  return m->distance_[code] + extra_bits_count;
+  int code, extra_bits;
+  VP8LPrefixEncodeBits(distance, &code, &extra_bits);
+  return m->distance_[code] + extra_bits;
+}
+
+static void AddSingleLiteralWithCostModel(
+    const uint32_t* const argb, VP8LHashChain* const hash_chain,
+    VP8LColorCache* const hashers, const CostModel* const cost_model, int idx,
+    int is_last, int use_color_cache, double prev_cost, float* const cost,
+    uint16_t* const dist_array) {
+  double cost_val = prev_cost;
+  const uint32_t color = argb[0];
+  if (!is_last) {
+    HashChainInsert(hash_chain, argb, idx);
+  }
+  if (use_color_cache && VP8LColorCacheContains(hashers, color)) {
+    const double mul0 = 0.68;
+    const int ix = VP8LColorCacheGetIndex(hashers, color);
+    cost_val += GetCacheCost(cost_model, ix) * mul0;
+  } else {
+    const double mul1 = 0.82;
+    if (use_color_cache) VP8LColorCacheInsert(hashers, color);
+    cost_val += GetLiteralCost(cost_model, color) * mul1;
+  }
+  if (cost[idx] > cost_val) {
+    cost[idx] = (float)cost_val;
+    dist_array[idx] = 1;  // only one is inserted.
+  }
 }
 
 static int BackwardReferencesHashChainDistanceOnly(
-    int xsize, int ysize, int recursive_cost_model, const uint32_t* const argb,
-    int cache_bits, uint32_t* const dist_array) {
+    int xsize, int ysize, const uint32_t* const argb,
+    int quality, int cache_bits, VP8LHashChain* const hash_chain,
+    VP8LBackwardRefs* const refs, uint16_t* const dist_array) {
   int i;
   int ok = 0;
   int cc_init = 0;
-  const int quality = 100;
   const int pix_count = xsize * ysize;
   const int use_color_cache = (cache_bits > 0);
-  double* const cost =
-      (double*)WebPSafeMalloc((uint64_t)pix_count, sizeof(*cost));
-  CostModel* cost_model = (CostModel*)malloc(sizeof(*cost_model));
-  HashChain* hash_chain = (HashChain*)malloc(sizeof(*hash_chain));
+  float* const cost =
+      (float*)WebPSafeMalloc(pix_count, sizeof(*cost));
+  const size_t literal_array_size = sizeof(double) *
+      (NUM_LITERAL_CODES + NUM_LENGTH_CODES +
+       ((cache_bits > 0) ? (1 << cache_bits) : 0));
+  const size_t cost_model_size = sizeof(CostModel) + literal_array_size;
+  CostModel* const cost_model =
+      (CostModel*)WebPSafeMalloc(1ULL, cost_model_size);
   VP8LColorCache hashers;
-  const double mul0 = (recursive_cost_model != 0) ? 1.0 : 0.68;
-  const double mul1 = (recursive_cost_model != 0) ? 1.0 : 0.82;
-
-  if (cost == NULL || cost_model == NULL || hash_chain == NULL) goto Error;
+  const int skip_length = 32 + quality;
+  const int skip_min_distance_code = 2;
+  int iter_max = GetMaxItersForQuality(quality, 0);
+  const int window_size = GetWindowSizeForHashChain(quality, xsize);
 
-  if (!HashChainInit(hash_chain, pix_count)) goto Error;
+  if (cost == NULL || cost_model == NULL) goto Error;
 
+  cost_model->literal_ = (double*)(cost_model + 1);
   if (use_color_cache) {
     cc_init = VP8LColorCacheInit(&hashers, cache_bits);
     if (!cc_init) goto Error;
   }
 
-  if (!CostModelBuild(cost_model, xsize, ysize, recursive_cost_model, argb,
-                      cache_bits)) {
+  if (!CostModelBuild(cost_model, cache_bits, refs)) {
     goto Error;
   }
 
-  for (i = 0; i < pix_count; ++i) cost[i] = 1e100;
+  for (i = 0; i < pix_count; ++i) cost[i] = 1e38f;
 
   // We loop one pixel at a time, but store all currently best points to
   // non-processed locations from this point.
   dist_array[0] = 0;
-  for (i = 0; i < pix_count; ++i) {
-    double prev_cost = 0.0;
-    int shortmax;
-    if (i > 0) {
-      prev_cost = cost[i - 1];
-    }
-    for (shortmax = 0; shortmax < 2; ++shortmax) {
-      int offset = 0;
-      int len = 0;
-      if (i < pix_count - 1) {  // FindCopy reads pixels at [i] and [i + 1].
-        int maxlen = shortmax ? 2 : MAX_LENGTH;
-        if (maxlen > pix_count - i) {
-          maxlen = pix_count - i;
+  HashChainReset(hash_chain);
+  // Add first pixel as literal.
+  AddSingleLiteralWithCostModel(argb + 0, hash_chain, &hashers, cost_model, 0,
+                                0, use_color_cache, 0.0, cost, dist_array);
+  for (i = 1; i < pix_count - 1; ++i) {
+    int offset = 0;
+    int len = 0;
+    double prev_cost = cost[i - 1];
+    const int max_len = MaxFindCopyLength(pix_count - i);
+    HashChainFindCopy(hash_chain, i, argb, max_len, window_size,
+                      iter_max, &offset, &len);
+    if (len >= MIN_LENGTH) {
+      const int code = DistanceToPlaneCode(xsize, offset);
+      const double distance_cost =
+          prev_cost + GetDistanceCost(cost_model, code);
+      int k;
+      for (k = 1; k < len; ++k) {
+        const double cost_val = distance_cost + GetLengthCost(cost_model, k);
+        if (cost[i + k] > cost_val) {
+          cost[i + k] = (float)cost_val;
+          dist_array[i + k] = k + 1;
         }
-        HashChainFindCopy(hash_chain, quality, i, xsize, argb, maxlen,
-                          &offset, &len);
       }
-      if (len >= MIN_LENGTH) {
-        const int code = DistanceToPlaneCode(xsize, offset);
-        const double distance_cost =
-            prev_cost + GetDistanceCost(cost_model, code);
-        int k;
-        for (k = 1; k < len; ++k) {
-          const double cost_val =
-              distance_cost + GetLengthCost(cost_model, k);
-          if (cost[i + k] > cost_val) {
-            cost[i + k] = cost_val;
-            dist_array[i + k] = k + 1;
+      // This if is for speedup only. It roughly doubles the speed, and
+      // makes compression worse by .1 %.
+      if (len >= skip_length && code <= skip_min_distance_code) {
+        // Long copy for short distances, let's skip the middle
+        // lookups for better copies.
+        // 1) insert the hashes.
+        if (use_color_cache) {
+          for (k = 0; k < len; ++k) {
+            VP8LColorCacheInsert(&hashers, argb[i + k]);
           }
         }
-        // This if is for speedup only. It roughly doubles the speed, and
-        // makes compression worse by .1 %.
-        if (len >= 128 && code < 2) {
-          // Long copy for short distances, let's skip the middle
-          // lookups for better copies.
-          // 1) insert the hashes.
-          if (use_color_cache) {
-            for (k = 0; k < len; ++k) {
-              VP8LColorCacheInsert(&hashers, argb[i + k]);
-            }
-          }
-          // 2) Add to the hash_chain (but cannot add the last pixel)
-          {
-            const int last = (len < pix_count - 1 - i) ? len
-                                                       : pix_count - 1 - i;
-            for (k = 0; k < last; ++k) {
-              HashChainInsert(hash_chain, &argb[i + k], i + k);
-            }
+        // 2) Add to the hash_chain (but cannot add the last pixel)
+        {
+          const int last = (len + i < pix_count - 1) ? len + i
+                                                     : pix_count - 1;
+          for (k = i; k < last; ++k) {
+            HashChainInsert(hash_chain, &argb[k], k);
           }
-          // 3) jump.
-          i += len - 1;  // for loop does ++i, thus -1 here.
-          goto next_symbol;
         }
+        // 3) jump.
+        i += len - 1;  // for loop does ++i, thus -1 here.
+        goto next_symbol;
       }
-    }
-    if (i < pix_count - 1) {
-      HashChainInsert(hash_chain, &argb[i], i);
-    }
-    {
-      // inserting a literal pixel
-      double cost_val = prev_cost;
-      if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
-        const int ix = VP8LColorCacheGetIndex(&hashers, argb[i]);
-        cost_val += GetCacheCost(cost_model, ix) * mul0;
-      } else {
-        cost_val += GetLiteralCost(cost_model, argb[i]) * mul1;
-      }
-      if (cost[i] > cost_val) {
-        cost[i] = cost_val;
-        dist_array[i] = 1;  // only one is inserted.
+      if (len != MIN_LENGTH) {
+        int code_min_length;
+        double cost_total;
+        HashChainFindOffset(hash_chain, i, argb, MIN_LENGTH, window_size,
+                            &offset);
+        code_min_length = DistanceToPlaneCode(xsize, offset);
+        cost_total = prev_cost +
+            GetDistanceCost(cost_model, code_min_length) +
+            GetLengthCost(cost_model, 1);
+        if (cost[i + 1] > cost_total) {
+          cost[i + 1] = (float)cost_total;
+          dist_array[i + 1] = 2;
+        }
       }
-      if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
     }
+    AddSingleLiteralWithCostModel(argb + i, hash_chain, &hashers, cost_model, i,
+                                  0, use_color_cache, prev_cost, cost,
+                                  dist_array);
  next_symbol: ;
   }
-  // Last pixel still to do, it can only be a single step if not reached
-  // through cheaper means already.
-  ok = 1;
-Error:
+  // Handle the last pixel.
+  if (i == (pix_count - 1)) {
+    AddSingleLiteralWithCostModel(argb + i, hash_chain, &hashers, cost_model, i,
+                                  1, use_color_cache, cost[pix_count - 2], cost,
+                                  dist_array);
+  }
+  ok = !refs->error_;
+ Error:
   if (cc_init) VP8LColorCacheClear(&hashers);
-  HashChainDelete(hash_chain);
-  free(cost_model);
-  free(cost);
+  WebPSafeFree(cost_model);
+  WebPSafeFree(cost);
   return ok;
 }
 
-static int TraceBackwards(const uint32_t* const dist_array,
-                          int dist_array_size,
-                          uint32_t** const chosen_path,
-                          int* const chosen_path_size) {
-  int i;
-  // Count how many.
-  int count = 0;
-  for (i = dist_array_size - 1; i >= 0; ) {
-    int k = dist_array[i];
-    assert(k >= 1);
-    ++count;
-    i -= k;
-  }
-  // Allocate.
-  *chosen_path_size = count;
-  *chosen_path =
-      (uint32_t*)WebPSafeMalloc((uint64_t)count, sizeof(**chosen_path));
-  if (*chosen_path == NULL) return 0;
-
-  // Write in reverse order.
-  for (i = dist_array_size - 1; i >= 0; ) {
-    int k = dist_array[i];
-    assert(k >= 1);
-    (*chosen_path)[--count] = k;
-    i -= k;
+// We pack the path at the end of *dist_array and return
+// a pointer to this part of the array. Example:
+// dist_array = [1x2xx3x2] => packed [1x2x1232], chosen_path = [1232]
+static void TraceBackwards(uint16_t* const dist_array,
+                           int dist_array_size,
+                           uint16_t** const chosen_path,
+                           int* const chosen_path_size) {
+  uint16_t* path = dist_array + dist_array_size;
+  uint16_t* cur = dist_array + dist_array_size - 1;
+  while (cur >= dist_array) {
+    const int k = *cur;
+    --path;
+    *path = k;
+    cur -= k;
   }
-  return 1;
+  *chosen_path = path;
+  *chosen_path_size = (int)(dist_array + dist_array_size - path);
 }
 
 static int BackwardReferencesHashChainFollowChosenPath(
-    int xsize, int ysize, const uint32_t* const argb, int cache_bits,
-    const uint32_t* const chosen_path, int chosen_path_size,
+    int xsize, int ysize, const uint32_t* const argb,
+    int quality, int cache_bits,
+    const uint16_t* const chosen_path, int chosen_path_size,
+    VP8LHashChain* const hash_chain,
     VP8LBackwardRefs* const refs) {
-  const int quality = 100;
   const int pix_count = xsize * ysize;
   const int use_color_cache = (cache_bits > 0);
-  int size = 0;
-  int i = 0;
-  int k;
   int ix;
+  int i = 0;
   int ok = 0;
   int cc_init = 0;
-  HashChain* hash_chain = (HashChain*)malloc(sizeof(*hash_chain));
+  const int window_size = GetWindowSizeForHashChain(quality, xsize);
   VP8LColorCache hashers;
 
-  if (hash_chain == NULL || !HashChainInit(hash_chain, pix_count)) {
-    goto Error;
-  }
   if (use_color_cache) {
     cc_init = VP8LColorCacheInit(&hashers, cache_bits);
     if (!cc_init) goto Error;
   }
 
-  refs->size = 0;
-  for (ix = 0; ix < chosen_path_size; ++ix, ++size) {
+  ClearBackwardRefs(refs);
+  HashChainReset(hash_chain);
+  for (ix = 0; ix < chosen_path_size; ++ix) {
     int offset = 0;
-    int len = 0;
-    int maxlen = chosen_path[ix];
-    if (maxlen != 1) {
-      HashChainFindCopy(hash_chain, quality,
-                        i, xsize, argb, maxlen, &offset, &len);
-      assert(len == maxlen);
-      refs->refs[size] = PixOrCopyCreateCopy(offset, len);
+    const int len = chosen_path[ix];
+    if (len != 1) {
+      int k;
+      HashChainFindOffset(hash_chain, i, argb, len, window_size, &offset);
+      BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(offset, len));
       if (use_color_cache) {
         for (k = 0; k < len; ++k) {
           VP8LColorCacheInsert(&hashers, argb[i + k]);
@@ -648,227 +780,330 @@ static int BackwardReferencesHashChainFollowChosenPath(
       }
       i += len;
     } else {
+      PixOrCopy v;
       if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
         // push pixel as a color cache index
         const int idx = VP8LColorCacheGetIndex(&hashers, argb[i]);
-        refs->refs[size] = PixOrCopyCreateCacheIdx(idx);
+        v = PixOrCopyCreateCacheIdx(idx);
       } else {
-        refs->refs[size] = PixOrCopyCreateLiteral(argb[i]);
+        if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
+        v = PixOrCopyCreateLiteral(argb[i]);
       }
-      if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
+      BackwardRefsCursorAdd(refs, v);
       if (i + 1 < pix_count) {
         HashChainInsert(hash_chain, &argb[i], i);
       }
       ++i;
     }
   }
-  assert(size <= refs->max_size);
-  refs->size = size;
-  ok = 1;
-Error:
+  ok = !refs->error_;
+ Error:
   if (cc_init) VP8LColorCacheClear(&hashers);
-  HashChainDelete(hash_chain);
   return ok;
 }
 
 // Returns 1 on success.
 static int BackwardReferencesTraceBackwards(int xsize, int ysize,
-                                            int recursive_cost_model,
                                             const uint32_t* const argb,
-                                            int cache_bits,
+                                            int quality, int cache_bits,
+                                            VP8LHashChain* const hash_chain,
                                             VP8LBackwardRefs* const refs) {
   int ok = 0;
   const int dist_array_size = xsize * ysize;
-  uint32_t* chosen_path = NULL;
+  uint16_t* chosen_path = NULL;
   int chosen_path_size = 0;
-  uint32_t* dist_array =
-      (uint32_t*)WebPSafeMalloc((uint64_t)dist_array_size, sizeof(*dist_array));
+  uint16_t* dist_array =
+      (uint16_t*)WebPSafeMalloc(dist_array_size, sizeof(*dist_array));
 
   if (dist_array == NULL) goto Error;
 
   if (!BackwardReferencesHashChainDistanceOnly(
-      xsize, ysize, recursive_cost_model, argb, cache_bits, dist_array)) {
-    goto Error;
-  }
-  if (!TraceBackwards(dist_array, dist_array_size,
-                      &chosen_path, &chosen_path_size)) {
+      xsize, ysize, argb, quality, cache_bits, hash_chain,
+      refs, dist_array)) {
     goto Error;
   }
-  free(dist_array);   // no need to retain this memory any longer
-  dist_array = NULL;
+  TraceBackwards(dist_array, dist_array_size, &chosen_path, &chosen_path_size);
   if (!BackwardReferencesHashChainFollowChosenPath(
-      xsize, ysize, argb, cache_bits, chosen_path, chosen_path_size, refs)) {
+      xsize, ysize, argb, quality, cache_bits, chosen_path, chosen_path_size,
+      hash_chain, refs)) {
     goto Error;
   }
   ok = 1;
  Error:
-  free(chosen_path);
-  free(dist_array);
+  WebPSafeFree(dist_array);
   return ok;
 }
 
 static void BackwardReferences2DLocality(int xsize,
-                                         VP8LBackwardRefs* const refs) {
-  int i;
-  for (i = 0; i < refs->size; ++i) {
-    if (PixOrCopyIsCopy(&refs->refs[i])) {
-      const int dist = refs->refs[i].argb_or_distance;
+                                         const VP8LBackwardRefs* const refs) {
+  VP8LRefsCursor c = VP8LRefsCursorInit(refs);
+  while (VP8LRefsCursorOk(&c)) {
+    if (PixOrCopyIsCopy(c.cur_pos)) {
+      const int dist = c.cur_pos->argb_or_distance;
       const int transformed_dist = DistanceToPlaneCode(xsize, dist);
-      refs->refs[i].argb_or_distance = transformed_dist;
+      c.cur_pos->argb_or_distance = transformed_dist;
     }
+    VP8LRefsCursorNext(&c);
   }
 }
 
-int VP8LGetBackwardReferences(int width, int height,
-                              const uint32_t* const argb,
-                              int quality, int cache_bits, int use_2d_locality,
-                              VP8LBackwardRefs* const best) {
-  int ok = 0;
-  int lz77_is_useful;
-  VP8LBackwardRefs refs_rle, refs_lz77;
-  const int num_pix = width * height;
-
-  VP8LBackwardRefsAlloc(&refs_rle, num_pix);
-  VP8LBackwardRefsAlloc(&refs_lz77, num_pix);
-  VP8LInitBackwardRefs(best);
-  if (refs_rle.refs == NULL || refs_lz77.refs == NULL) {
- Error1:
-    VP8LClearBackwardRefs(&refs_rle);
-    VP8LClearBackwardRefs(&refs_lz77);
-    goto End;
-  }
-
-  if (!BackwardReferencesHashChain(width, height, argb, cache_bits, quality,
-                                   &refs_lz77)) {
-    goto End;
-  }
-  // Backward Reference using RLE only.
-  BackwardReferencesRle(width, height, argb, &refs_rle);
+// Returns entropy for the given cache bits.
+static double ComputeCacheEntropy(const uint32_t* argb,
+                                  const VP8LBackwardRefs* const refs,
+                                  int cache_bits) {
+  const int use_color_cache = (cache_bits > 0);
+  int cc_init = 0;
+  double entropy = MAX_ENTROPY;
+  const double kSmallPenaltyForLargeCache = 4.0;
+  VP8LColorCache hashers;
+  VP8LRefsCursor c = VP8LRefsCursorInit(refs);
+  VP8LHistogram* histo = VP8LAllocateHistogram(cache_bits);
+  if (histo == NULL) goto Error;
 
-  {
-    double bit_cost_lz77, bit_cost_rle;
-    VP8LHistogram* const histo = (VP8LHistogram*)malloc(sizeof(*histo));
-    if (histo == NULL) goto Error1;
-    // Evaluate lz77 coding
-    VP8LHistogramCreate(histo, &refs_lz77, cache_bits);
-    bit_cost_lz77 = VP8LHistogramEstimateBits(histo);
-    // Evaluate RLE coding
-    VP8LHistogramCreate(histo, &refs_rle, cache_bits);
-    bit_cost_rle = VP8LHistogramEstimateBits(histo);
-    // Decide if LZ77 is useful.
-    lz77_is_useful = (bit_cost_lz77 < bit_cost_rle);
-    free(histo);
+  if (use_color_cache) {
+    cc_init = VP8LColorCacheInit(&hashers, cache_bits);
+    if (!cc_init) goto Error;
   }
-
-  // Choose appropriate backward reference.
-  if (lz77_is_useful) {
-    // TraceBackwards is costly. Run it for higher qualities.
-    const int try_lz77_trace_backwards = (quality >= 75);
-    *best = refs_lz77;   // default guess: lz77 is better
-    VP8LClearBackwardRefs(&refs_rle);
-    if (try_lz77_trace_backwards) {
-      const int recursion_level = (num_pix < 320 * 200) ? 1 : 0;
-      VP8LBackwardRefs refs_trace;
-      if (!VP8LBackwardRefsAlloc(&refs_trace, num_pix)) {
-        goto End;
-      }
-      if (BackwardReferencesTraceBackwards(
-          width, height, recursion_level, argb, cache_bits, &refs_trace)) {
-        VP8LClearBackwardRefs(&refs_lz77);
-        *best = refs_trace;
-      }
+  if (!use_color_cache) {
+    while (VP8LRefsCursorOk(&c)) {
+      VP8LHistogramAddSinglePixOrCopy(histo, c.cur_pos);
+      VP8LRefsCursorNext(&c);
     }
   } else {
-    VP8LClearBackwardRefs(&refs_lz77);
-    *best = refs_rle;
+    while (VP8LRefsCursorOk(&c)) {
+      const PixOrCopy* const v = c.cur_pos;
+      if (PixOrCopyIsLiteral(v)) {
+        const uint32_t pix = *argb++;
+        const uint32_t key = VP8LColorCacheGetIndex(&hashers, pix);
+        if (VP8LColorCacheLookup(&hashers, key) == pix) {
+          ++histo->literal_[NUM_LITERAL_CODES + NUM_LENGTH_CODES + key];
+        } else {
+          VP8LColorCacheSet(&hashers, key, pix);
+          ++histo->blue_[pix & 0xff];
+          ++histo->literal_[(pix >> 8) & 0xff];
+          ++histo->red_[(pix >> 16) & 0xff];
+          ++histo->alpha_[pix >> 24];
+        }
+      } else {
+        int len = PixOrCopyLength(v);
+        int code, extra_bits;
+        VP8LPrefixEncodeBits(len, &code, &extra_bits);
+        ++histo->literal_[NUM_LITERAL_CODES + code];
+        VP8LPrefixEncodeBits(PixOrCopyDistance(v), &code, &extra_bits);
+        ++histo->distance_[code];
+        do {
+          VP8LColorCacheInsert(&hashers, *argb++);
+        } while(--len != 0);
+      }
+      VP8LRefsCursorNext(&c);
+    }
   }
+  entropy = VP8LHistogramEstimateBits(histo) +
+      kSmallPenaltyForLargeCache * cache_bits;
+ Error:
+  if (cc_init) VP8LColorCacheClear(&hashers);
+  VP8LFreeHistogram(histo);
+  return entropy;
+}
 
-  if (use_2d_locality) BackwardReferences2DLocality(width, best);
-
-  ok = 1;
-
- End:
-  if (!ok) {
-    VP8LClearBackwardRefs(best);
+// Evaluate optimal cache bits for the local color cache.
+// The input *best_cache_bits sets the maximum cache bits to use (passing 0
+// implies disabling the local color cache). The local color cache is also
+// disabled for the lower (<= 25) quality.
+// Returns 0 in case of memory error.
+static int CalculateBestCacheSize(const uint32_t* const argb,
+                                  int xsize, int ysize, int quality,
+                                  VP8LHashChain* const hash_chain,
+                                  VP8LBackwardRefs* const refs,
+                                  int* const lz77_computed,
+                                  int* const best_cache_bits) {
+  int eval_low = 1;
+  int eval_high = 1;
+  double entropy_low = MAX_ENTROPY;
+  double entropy_high = MAX_ENTROPY;
+  const double cost_mul = 5e-4;
+  int cache_bits_low = 0;
+  int cache_bits_high = (quality <= 25) ? 0 : *best_cache_bits;
+
+  assert(cache_bits_high <= MAX_COLOR_CACHE_BITS);
+
+  *lz77_computed = 0;
+  if (cache_bits_high == 0) {
+    *best_cache_bits = 0;
+    // Local color cache is disabled.
+    return 1;
   }
-  return ok;
+  if (!BackwardReferencesLz77(xsize, ysize, argb, cache_bits_low, quality, 0,
+                              hash_chain, refs)) {
+    return 0;
+  }
+  // Do a binary search to find the optimal entropy for cache_bits.
+  while (eval_low || eval_high) {
+    if (eval_low) {
+      entropy_low = ComputeCacheEntropy(argb, refs, cache_bits_low);
+      entropy_low += entropy_low * cache_bits_low * cost_mul;
+      eval_low = 0;
+    }
+    if (eval_high) {
+      entropy_high = ComputeCacheEntropy(argb, refs, cache_bits_high);
+      entropy_high += entropy_high * cache_bits_high * cost_mul;
+      eval_high = 0;
+    }
+    if (entropy_high < entropy_low) {
+      const int prev_cache_bits_low = cache_bits_low;
+      *best_cache_bits = cache_bits_high;
+      cache_bits_low = (cache_bits_low + cache_bits_high) / 2;
+      if (cache_bits_low != prev_cache_bits_low) eval_low = 1;
+    } else {
+      *best_cache_bits = cache_bits_low;
+      cache_bits_high = (cache_bits_low + cache_bits_high) / 2;
+      if (cache_bits_high != cache_bits_low) eval_high = 1;
+    }
+  }
+  *lz77_computed = 1;
+  return 1;
 }
 
-// Returns 1 on success.
-static int ComputeCacheHistogram(const uint32_t* const argb,
-                                 int xsize, int ysize,
-                                 const VP8LBackwardRefs* const refs,
-                                 int cache_bits,
-                                 VP8LHistogram* const histo) {
+// Update (in-place) backward references for specified cache_bits.
+static int BackwardRefsWithLocalCache(const uint32_t* const argb,
+                                      int cache_bits,
+                                      VP8LBackwardRefs* const refs) {
   int pixel_index = 0;
-  int i;
-  uint32_t k;
   VP8LColorCache hashers;
-  const int use_color_cache = (cache_bits > 0);
-  int cc_init = 0;
+  VP8LRefsCursor c = VP8LRefsCursorInit(refs);
+  if (!VP8LColorCacheInit(&hashers, cache_bits)) return 0;
 
-  if (use_color_cache) {
-    cc_init = VP8LColorCacheInit(&hashers, cache_bits);
-    if (!cc_init) return 0;
-  }
-
-  for (i = 0; i < refs->size; ++i) {
-    const PixOrCopy* const v = &refs->refs[i];
+  while (VP8LRefsCursorOk(&c)) {
+    PixOrCopy* const v = c.cur_pos;
     if (PixOrCopyIsLiteral(v)) {
-      if (use_color_cache &&
-          VP8LColorCacheContains(&hashers, argb[pixel_index])) {
-        // push pixel as a cache index
-        const int ix = VP8LColorCacheGetIndex(&hashers, argb[pixel_index]);
-        const PixOrCopy token = PixOrCopyCreateCacheIdx(ix);
-        VP8LHistogramAddSinglePixOrCopy(histo, &token);
+      const uint32_t argb_literal = v->argb_or_distance;
+      if (VP8LColorCacheContains(&hashers, argb_literal)) {
+        const int ix = VP8LColorCacheGetIndex(&hashers, argb_literal);
+        *v = PixOrCopyCreateCacheIdx(ix);
       } else {
-        VP8LHistogramAddSinglePixOrCopy(histo, v);
+        VP8LColorCacheInsert(&hashers, argb_literal);
       }
+      ++pixel_index;
     } else {
-      VP8LHistogramAddSinglePixOrCopy(histo, v);
-    }
-    if (use_color_cache) {
-      for (k = 0; k < PixOrCopyLength(v); ++k) {
-        VP8LColorCacheInsert(&hashers, argb[pixel_index + k]);
+      // refs was created without local cache, so it can not have cache indexes.
+      int k;
+      assert(PixOrCopyIsCopy(v));
+      for (k = 0; k < v->len; ++k) {
+        VP8LColorCacheInsert(&hashers, argb[pixel_index++]);
       }
     }
-    pixel_index += PixOrCopyLength(v);
+    VP8LRefsCursorNext(&c);
   }
-  assert(pixel_index == xsize * ysize);
-  (void)xsize;  // xsize is not used in non-debug compilations otherwise.
-  (void)ysize;  // ysize is not used in non-debug compilations otherwise.
-  if (cc_init) VP8LColorCacheClear(&hashers);
+  VP8LColorCacheClear(&hashers);
   return 1;
 }
 
-// Returns how many bits are to be used for a color cache.
-int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
-                                      int xsize, int ysize,
-                                      int* const best_cache_bits) {
-  int ok = 0;
-  int cache_bits;
-  double lowest_entropy = 1e99;
-  VP8LBackwardRefs refs;
-  static const double kSmallPenaltyForLargeCache = 4.0;
-  static const int quality = 30;
-  if (!VP8LBackwardRefsAlloc(&refs, xsize * ysize) ||
-      !BackwardReferencesHashChain(xsize, ysize, argb, 0, quality, &refs)) {
+static VP8LBackwardRefs* GetBackwardReferencesLowEffort(
+    int width, int height, const uint32_t* const argb, int quality,
+    int* const cache_bits, VP8LHashChain* const hash_chain,
+    VP8LBackwardRefs refs_array[2]) {
+  VP8LBackwardRefs* refs_lz77 = &refs_array[0];
+  *cache_bits = 0;
+  if (!BackwardReferencesLz77(width, height, argb, 0, quality,
+                              1 /* Low effort. */, hash_chain, refs_lz77)) {
+    return NULL;
+  }
+  BackwardReferences2DLocality(width, refs_lz77);
+  return refs_lz77;
+}
+
+static VP8LBackwardRefs* GetBackwardReferences(
+    int width, int height, const uint32_t* const argb, int quality,
+    int* const cache_bits, VP8LHashChain* const hash_chain,
+    VP8LBackwardRefs refs_array[2]) {
+  int lz77_is_useful;
+  int lz77_computed;
+  double bit_cost_lz77, bit_cost_rle;
+  VP8LBackwardRefs* best = NULL;
+  VP8LBackwardRefs* refs_lz77 = &refs_array[0];
+  VP8LBackwardRefs* refs_rle = &refs_array[1];
+  VP8LHistogram* histo = NULL;
+
+  if (!CalculateBestCacheSize(argb, width, height, quality, hash_chain,
+                              refs_lz77, &lz77_computed, cache_bits)) {
     goto Error;
   }
-  for (cache_bits = 0; cache_bits <= MAX_COLOR_CACHE_BITS; ++cache_bits) {
-    double cur_entropy;
-    VP8LHistogram histo;
-    VP8LHistogramInit(&histo, cache_bits);
-    ComputeCacheHistogram(argb, xsize, ysize, &refs, cache_bits, &histo);
-    cur_entropy = VP8LHistogramEstimateBits(&histo) +
-        kSmallPenaltyForLargeCache * cache_bits;
-    if (cache_bits == 0 || cur_entropy < lowest_entropy) {
-      *best_cache_bits = cache_bits;
-      lowest_entropy = cur_entropy;
+
+  if (lz77_computed) {
+    // Transform refs_lz77 for the optimized cache_bits.
+    if (*cache_bits > 0) {
+      if (!BackwardRefsWithLocalCache(argb, *cache_bits, refs_lz77)) {
+        goto Error;
+      }
+    }
+  } else {
+    if (!BackwardReferencesLz77(width, height, argb, *cache_bits, quality,
+                                0 /* Low effort. */, hash_chain, refs_lz77)) {
+      goto Error;
     }
   }
-  ok = 1;
+
+  if (!BackwardReferencesRle(width, height, argb, *cache_bits, refs_rle)) {
+    goto Error;
+  }
+
+  histo = VP8LAllocateHistogram(*cache_bits);
+  if (histo == NULL) goto Error;
+
+  {
+    // Evaluate LZ77 coding.
+    VP8LHistogramCreate(histo, refs_lz77, *cache_bits);
+    bit_cost_lz77 = VP8LHistogramEstimateBits(histo);
+    // Evaluate RLE coding.
+    VP8LHistogramCreate(histo, refs_rle, *cache_bits);
+    bit_cost_rle = VP8LHistogramEstimateBits(histo);
+    // Decide if LZ77 is useful.
+    lz77_is_useful = (bit_cost_lz77 < bit_cost_rle);
+  }
+
+  // Choose appropriate backward reference.
+  if (lz77_is_useful) {
+    // TraceBackwards is costly. Don't execute it at lower quality.
+    const int try_lz77_trace_backwards = (quality >= 25);
+    best = refs_lz77;   // default guess: lz77 is better
+    if (try_lz77_trace_backwards) {
+      VP8LBackwardRefs* const refs_trace = refs_rle;
+      if (!VP8LBackwardRefsCopy(refs_lz77, refs_trace)) {
+        best = NULL;
+        goto Error;
+      }
+      if (BackwardReferencesTraceBackwards(width, height, argb, quality,
+                                           *cache_bits, hash_chain,
+                                           refs_trace)) {
+        double bit_cost_trace;
+        // Evaluate LZ77 coding.
+        VP8LHistogramCreate(histo, refs_trace, *cache_bits);
+        bit_cost_trace = VP8LHistogramEstimateBits(histo);
+        if (bit_cost_trace < bit_cost_lz77) {
+          best = refs_trace;
+        }
+      }
+    }
+  } else {
+    best = refs_rle;
+  }
+
+  BackwardReferences2DLocality(width, best);
+
  Error:
-  VP8LClearBackwardRefs(&refs);
-  return ok;
+  VP8LFreeHistogram(histo);
+  return best;
+}
+
+VP8LBackwardRefs* VP8LGetBackwardReferences(
+    int width, int height, const uint32_t* const argb, int quality,
+    int low_effort, int* const cache_bits, VP8LHashChain* const hash_chain,
+    VP8LBackwardRefs refs_array[2]) {
+  if (low_effort) {
+    return GetBackwardReferencesLowEffort(width, height, argb, quality,
+                                          cache_bits, hash_chain, refs_array);
+  } else {
+    return GetBackwardReferences(width, height, argb, quality, cache_bits,
+                                 hash_chain, refs_array);
+  }
 }
diff --git a/drivers/webp/enc/backward_references.h b/drivers/webp/enc/backward_references.h
index 8006a56ba1..daa084d846 100644
--- a/drivers/webp/enc/backward_references.h
+++ b/drivers/webp/enc/backward_references.h
@@ -1,8 +1,10 @@
 // Copyright 2012 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Author: Jyrki Alakuijala (jyrki@google.com)
@@ -13,82 +15,15 @@
 
 #include <assert.h>
 #include <stdlib.h>
-#include "../types.h"
-#include "../format_constants.h"
+#include "../webp/types.h"
+#include "../webp/format_constants.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
-// The spec allows 11, we use 9 bits to reduce memory consumption in encoding.
-// Having 9 instead of 11 only removes about 0.25 % of compression density.
-#define MAX_COLOR_CACHE_BITS 9
-
-// Max ever number of codes we'll use:
-#define PIX_OR_COPY_CODES_MAX \
-    (NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS))
-
-// -----------------------------------------------------------------------------
-// PrefixEncode()
-
-// use GNU builtins where available.
-#if defined(__GNUC__) && \
-    ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
-static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
-  return n == 0 ? -1 : 31 ^ __builtin_clz(n);
-}
-#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86))
-#include <intrin.h>
-#pragma intrinsic(_BitScanReverse)
-
-static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
-  unsigned long first_set_bit;
-  return _BitScanReverse(&first_set_bit, n) ? first_set_bit : -1;
-}
-#else
-static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
-  int log = 0;
-  uint32_t value = n;
-  int i;
-
-  if (value == 0) return -1;
-  for (i = 4; i >= 0; --i) {
-    const int shift = (1 << i);
-    const uint32_t x = value >> shift;
-    if (x != 0) {
-      value = x;
-      log += shift;
-    }
-  }
-  return log;
-}
-#endif
-
-static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) {
-  const int floor = BitsLog2Floor(n);
-  if (n == (n & ~(n - 1)))  // zero or a power of two.
-    return floor;
-  else
-    return floor + 1;
-}
-
-// Splitting of distance and length codes into prefixes and
-// extra bits. The prefixes are encoded with an entropy code
-// while the extra bits are stored just as normal bits.
-static WEBP_INLINE void PrefixEncode(int distance, int* const code,
-                                     int* const extra_bits_count,
-                                     int* const extra_bits_value) {
-  // Collect the two most significant bits where the highest bit is 1.
-  const int highest_bit = BitsLog2Floor(--distance);
-  // & 0x3f is to make behavior well defined when highest_bit
-  // does not exist or is the least significant bit.
-  const int second_highest_bit =
-      (distance >> ((highest_bit - 1) & 0x3f)) & 1;
-  *extra_bits_count = (highest_bit > 0) ? (highest_bit - 1) : 0;
-  *extra_bits_value = distance & ((1 << *extra_bits_count) - 1);
-  *code = (highest_bit > 0) ? (2 * highest_bit + second_highest_bit)
-                            : (highest_bit == 0) ? 1 : 0;
-}
+// The maximum allowed limit is 11.
+#define MAX_COLOR_CACHE_BITS 10
 
 // -----------------------------------------------------------------------------
 // PixOrCopy
@@ -173,39 +108,94 @@ static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
 }
 
 // -----------------------------------------------------------------------------
-// VP8LBackwardRefs
+// VP8LHashChain
+
+#define HASH_BITS 18
+#define HASH_SIZE (1 << HASH_BITS)
+
+typedef struct VP8LHashChain VP8LHashChain;
+struct VP8LHashChain {
+  // Stores the most recently added position with the given hash value.
+  int32_t hash_to_first_index_[HASH_SIZE];
+  // chain_[pos] stores the previous position with the same hash value
+  // for every pixel in the image.
+  int32_t* chain_;
+  // This is the maximum size of the hash_chain that can be constructed.
+  // Typically this is the pixel count (width x height) for a given image.
+  int size_;
+};
 
-typedef struct {
-  PixOrCopy* refs;
-  int size;      // currently used
-  int max_size;  // maximum capacity
-} VP8LBackwardRefs;
+// Must be called first, to set size.
+int VP8LHashChainInit(VP8LHashChain* const p, int size);
+void VP8LHashChainClear(VP8LHashChain* const p);  // release memory
 
-// Initialize the object. Must be called first. 'refs' can be NULL.
-void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs);
+// -----------------------------------------------------------------------------
+// VP8LBackwardRefs (block-based backward-references storage)
+
+// maximum number of reference blocks the image will be segmented into
+#define MAX_REFS_BLOCK_PER_IMAGE 16
+
+typedef struct PixOrCopyBlock PixOrCopyBlock;   // forward declaration
+typedef struct VP8LBackwardRefs VP8LBackwardRefs;
+
+// Container for blocks chain
+struct VP8LBackwardRefs {
+  int block_size_;               // common block-size
+  int error_;                    // set to true if some memory error occurred
+  PixOrCopyBlock* refs_;         // list of currently used blocks
+  PixOrCopyBlock** tail_;        // for list recycling
+  PixOrCopyBlock* free_blocks_;  // free-list
+  PixOrCopyBlock* last_block_;   // used for adding new refs (internal)
+};
 
-// Release memory and re-initialize the object. 'refs' can be NULL.
-void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs);
+// Initialize the object. 'block_size' is the common block size to store
+// references (typically, width * height / MAX_REFS_BLOCK_PER_IMAGE).
+void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size);
+// Release memory for backward references.
+void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs);
+// Copies the 'src' backward refs to the 'dst'. Returns 0 in case of error.
+int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
+                         VP8LBackwardRefs* const dst);
 
-// Allocate 'max_size' references. Returns false in case of memory error.
-int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size);
+// Cursor for iterating on references content
+typedef struct {
+  // public:
+  PixOrCopy* cur_pos;           // current position
+  // private:
+  PixOrCopyBlock* cur_block_;   // current block in the refs list
+  const PixOrCopy* last_pos_;   // sentinel for switching to next block
+} VP8LRefsCursor;
+
+// Returns a cursor positioned at the beginning of the references list.
+VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs);
+// Returns true if cursor is pointing at a valid position.
+static WEBP_INLINE int VP8LRefsCursorOk(const VP8LRefsCursor* const c) {
+  return (c->cur_pos != NULL);
+}
+// Move to next block of references. Internal, not to be called directly.
+void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c);
+// Move to next position, or NULL. Should not be called if !VP8LRefsCursorOk().
+static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
+  assert(c != NULL);
+  assert(VP8LRefsCursorOk(c));
+  if (++c->cur_pos == c->last_pos_) VP8LRefsCursorNextBlock(c);
+}
 
 // -----------------------------------------------------------------------------
 // Main entry points
 
 // Evaluates best possible backward references for specified quality.
-// Further optimize for 2D locality if use_2d_locality flag is set.
-int VP8LGetBackwardReferences(int width, int height,
-                              const uint32_t* const argb,
-                              int quality, int cache_bits, int use_2d_locality,
-                              VP8LBackwardRefs* const best);
-
-// Produce an estimate for a good color cache size for the image.
-int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
-                                      int xsize, int ysize,
-                                      int* const best_cache_bits);
-
-#if defined(__cplusplus) || defined(c_plusplus)
+// The input cache_bits to 'VP8LGetBackwardReferences' sets the maximum cache
+// bits to use (passing 0 implies disabling the local color cache).
+// The optimal cache bits is evaluated and set for the *cache_bits parameter.
+// The return value is the pointer to the best of the two backward refs viz,
+// refs[0] or refs[1].
+VP8LBackwardRefs* VP8LGetBackwardReferences(
+    int width, int height, const uint32_t* const argb, int quality,
+    int low_effort, int* const cache_bits, VP8LHashChain* const hash_chain,
+    VP8LBackwardRefs refs[2]);
+
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/drivers/webp/enc/config.c b/drivers/webp/enc/config.c
index 4136f6c227..f9f7961d58 100644
--- a/drivers/webp/enc/config.c
+++ b/drivers/webp/enc/config.c
@@ -1,19 +1,17 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Coding tools configuration
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
-#include "../encode.h"
-
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
+#include "../webp/encode.h"
 
 //------------------------------------------------------------------------------
 // WebPConfig
@@ -31,9 +29,9 @@ int WebPConfigInitInternal(WebPConfig* config,
   config->target_PSNR = 0.;
   config->method = 4;
   config->sns_strength = 50;
-  config->filter_strength = 20;   // default: light filtering
+  config->filter_strength = 60;   // mid-filtering
   config->filter_sharpness = 0;
-  config->filter_type = 0;        // default: simple
+  config->filter_type = 1;        // default: strong (so U/V is filtered too)
   config->partitions = 0;
   config->segments = 4;
   config->pass = 1;
@@ -45,7 +43,15 @@ int WebPConfigInitInternal(WebPConfig* config,
   config->alpha_filtering = 1;
   config->alpha_quality = 100;
   config->lossless = 0;
+  config->exact = 0;
   config->image_hint = WEBP_HINT_DEFAULT;
+  config->emulate_jpeg_size = 0;
+  config->thread_level = 0;
+  config->low_memory = 0;
+  config->near_lossless = 100;
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+  config->delta_palettization = 0;
+#endif // WEBP_EXPERIMENTAL_FEATURES
 
   // TODO(skal): tune.
   switch (preset) {
@@ -53,11 +59,13 @@ int WebPConfigInitInternal(WebPConfig* config,
       config->sns_strength = 80;
       config->filter_sharpness = 4;
       config->filter_strength = 35;
+      config->preprocessing &= ~2;   // no dithering
       break;
     case WEBP_PRESET_PHOTO:
       config->sns_strength = 80;
       config->filter_sharpness = 3;
       config->filter_strength = 30;
+      config->preprocessing |= 2;
       break;
     case WEBP_PRESET_DRAWING:
       config->sns_strength = 25;
@@ -67,10 +75,12 @@ int WebPConfigInitInternal(WebPConfig* config,
     case WEBP_PRESET_ICON:
       config->sns_strength = 0;
       config->filter_strength = 0;   // disable filtering to retain sharpness
+      config->preprocessing &= ~2;   // no dithering
       break;
     case WEBP_PRESET_TEXT:
       config->sns_strength = 0;
       config->filter_strength = 0;   // disable filtering to retain sharpness
+      config->preprocessing &= ~2;   // no dithering
       config->segments = 2;
       break;
     case WEBP_PRESET_DEFAULT:
@@ -106,7 +116,7 @@ int WebPValidateConfig(const WebPConfig* config) {
     return 0;
   if (config->show_compressed < 0 || config->show_compressed > 1)
     return 0;
-  if (config->preprocessing < 0 || config->preprocessing > 1)
+  if (config->preprocessing < 0 || config->preprocessing > 7)
     return 0;
   if (config->partitions < 0 || config->partitions > 3)
     return 0;
@@ -120,13 +130,44 @@ int WebPValidateConfig(const WebPConfig* config) {
     return 0;
   if (config->lossless < 0 || config->lossless > 1)
     return 0;
+  if (config->near_lossless < 0 || config->near_lossless > 100)
+    return 0;
   if (config->image_hint >= WEBP_HINT_LAST)
     return 0;
+  if (config->emulate_jpeg_size < 0 || config->emulate_jpeg_size > 1)
+    return 0;
+  if (config->thread_level < 0 || config->thread_level > 1)
+    return 0;
+  if (config->low_memory < 0 || config->low_memory > 1)
+    return 0;
+  if (config->exact < 0 || config->exact > 1)
+    return 0;
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+  if (config->delta_palettization < 0 || config->delta_palettization > 1)
+    return 0;
+#endif  // WEBP_EXPERIMENTAL_FEATURES
   return 1;
 }
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
+#define MAX_LEVEL 9
+
+// Mapping between -z level and -m / -q parameter settings.
+static const struct {
+  uint8_t method_;
+  uint8_t quality_;
+} kLosslessPresets[MAX_LEVEL + 1] = {
+  { 0,  0 }, { 1, 20 }, { 2, 25 }, { 3, 30 }, { 3, 50 },
+  { 4, 50 }, { 4, 75 }, { 4, 90 }, { 5, 90 }, { 6, 100 }
+};
+
+int WebPConfigLosslessPreset(WebPConfig* config, int level) {
+  if (config == NULL || level < 0 || level > MAX_LEVEL) return 0;
+  config->lossless = 1;
+  config->method = kLosslessPresets[level].method_;
+  config->quality = kLosslessPresets[level].quality_;
+  return 1;
+}
+
+//------------------------------------------------------------------------------
diff --git a/drivers/webp/enc/cost.c b/drivers/webp/enc/cost.c
index 92e0cc713c..ae7fe01388 100644
--- a/drivers/webp/enc/cost.c
+++ b/drivers/webp/enc/cost.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Cost tables for level and modes
@@ -11,42 +13,6 @@
 
 #include "./cost.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
-//------------------------------------------------------------------------------
-// Boolean-cost cost table
-
-const uint16_t VP8EntropyCost[256] = {
-  1792, 1792, 1792, 1536, 1536, 1408, 1366, 1280, 1280, 1216,
-  1178, 1152, 1110, 1076, 1061, 1024, 1024,  992,  968,  951,
-   939,  911,  896,  878,  871,  854,  838,  820,  811,  794,
-   786,  768,  768,  752,  740,  732,  720,  709,  704,  690,
-   683,  672,  666,  655,  647,  640,  631,  622,  615,  607,
-   598,  592,  586,  576,  572,  564,  559,  555,  547,  541,
-   534,  528,  522,  512,  512,  504,  500,  494,  488,  483,
-   477,  473,  467,  461,  458,  452,  448,  443,  438,  434,
-   427,  424,  419,  415,  410,  406,  403,  399,  394,  390,
-   384,  384,  377,  374,  370,  366,  362,  359,  355,  351,
-   347,  342,  342,  336,  333,  330,  326,  323,  320,  316,
-   312,  308,  305,  302,  299,  296,  293,  288,  287,  283,
-   280,  277,  274,  272,  268,  266,  262,  256,  256,  256,
-   251,  248,  245,  242,  240,  237,  234,  232,  228,  226,
-   223,  221,  218,  216,  214,  211,  208,  205,  203,  201,
-   198,  196,  192,  191,  188,  187,  183,  181,  179,  176,
-   175,  171,  171,  168,  165,  163,  160,  159,  156,  154,
-   152,  150,  148,  146,  144,  142,  139,  138,  135,  133,
-   131,  128,  128,  125,  123,  121,  119,  117,  115,  113,
-   111,  110,  107,  105,  103,  102,  100,   98,   96,   94,
-    92,   91,   89,   86,   86,   83,   82,   80,   77,   76,
-    74,   73,   71,   69,   67,   66,   64,   63,   61,   59,
-    57,   55,   54,   52,   51,   49,   47,   46,   44,   43,
-    41,   40,   38,   36,   35,   33,   32,   30,   29,   27,
-    25,   24,   22,   21,   19,   18,   16,   15,   13,   12,
-    10,    9,    7,    6,    4,    3
-};
-
 //------------------------------------------------------------------------------
 // Level cost tables
 
@@ -73,267 +39,6 @@ const uint16_t VP8LevelCodes[MAX_VARIABLE_LEVEL][2] = {
   {0x153, 0x053}, {0x153, 0x053}, {0x153, 0x053}, {0x153, 0x153}
 };
 
-// fixed costs for coding levels, deduce from the coding tree.
-// This is only the part that doesn't depend on the probability state.
-const uint16_t VP8LevelFixedCosts[2048] = {
-     0,  256,  256,  256,  256,  432,  618,  630,
-   731,  640,  640,  828,  901,  948, 1021, 1101,
-  1174, 1221, 1294, 1042, 1085, 1115, 1158, 1202,
-  1245, 1275, 1318, 1337, 1380, 1410, 1453, 1497,
-  1540, 1570, 1613, 1280, 1295, 1317, 1332, 1358,
-  1373, 1395, 1410, 1454, 1469, 1491, 1506, 1532,
-  1547, 1569, 1584, 1601, 1616, 1638, 1653, 1679,
-  1694, 1716, 1731, 1775, 1790, 1812, 1827, 1853,
-  1868, 1890, 1905, 1727, 1733, 1742, 1748, 1759,
-  1765, 1774, 1780, 1800, 1806, 1815, 1821, 1832,
-  1838, 1847, 1853, 1878, 1884, 1893, 1899, 1910,
-  1916, 1925, 1931, 1951, 1957, 1966, 1972, 1983,
-  1989, 1998, 2004, 2027, 2033, 2042, 2048, 2059,
-  2065, 2074, 2080, 2100, 2106, 2115, 2121, 2132,
-  2138, 2147, 2153, 2178, 2184, 2193, 2199, 2210,
-  2216, 2225, 2231, 2251, 2257, 2266, 2272, 2283,
-  2289, 2298, 2304, 2168, 2174, 2183, 2189, 2200,
-  2206, 2215, 2221, 2241, 2247, 2256, 2262, 2273,
-  2279, 2288, 2294, 2319, 2325, 2334, 2340, 2351,
-  2357, 2366, 2372, 2392, 2398, 2407, 2413, 2424,
-  2430, 2439, 2445, 2468, 2474, 2483, 2489, 2500,
-  2506, 2515, 2521, 2541, 2547, 2556, 2562, 2573,
-  2579, 2588, 2594, 2619, 2625, 2634, 2640, 2651,
-  2657, 2666, 2672, 2692, 2698, 2707, 2713, 2724,
-  2730, 2739, 2745, 2540, 2546, 2555, 2561, 2572,
-  2578, 2587, 2593, 2613, 2619, 2628, 2634, 2645,
-  2651, 2660, 2666, 2691, 2697, 2706, 2712, 2723,
-  2729, 2738, 2744, 2764, 2770, 2779, 2785, 2796,
-  2802, 2811, 2817, 2840, 2846, 2855, 2861, 2872,
-  2878, 2887, 2893, 2913, 2919, 2928, 2934, 2945,
-  2951, 2960, 2966, 2991, 2997, 3006, 3012, 3023,
-  3029, 3038, 3044, 3064, 3070, 3079, 3085, 3096,
-  3102, 3111, 3117, 2981, 2987, 2996, 3002, 3013,
-  3019, 3028, 3034, 3054, 3060, 3069, 3075, 3086,
-  3092, 3101, 3107, 3132, 3138, 3147, 3153, 3164,
-  3170, 3179, 3185, 3205, 3211, 3220, 3226, 3237,
-  3243, 3252, 3258, 3281, 3287, 3296, 3302, 3313,
-  3319, 3328, 3334, 3354, 3360, 3369, 3375, 3386,
-  3392, 3401, 3407, 3432, 3438, 3447, 3453, 3464,
-  3470, 3479, 3485, 3505, 3511, 3520, 3526, 3537,
-  3543, 3552, 3558, 2816, 2822, 2831, 2837, 2848,
-  2854, 2863, 2869, 2889, 2895, 2904, 2910, 2921,
-  2927, 2936, 2942, 2967, 2973, 2982, 2988, 2999,
-  3005, 3014, 3020, 3040, 3046, 3055, 3061, 3072,
-  3078, 3087, 3093, 3116, 3122, 3131, 3137, 3148,
-  3154, 3163, 3169, 3189, 3195, 3204, 3210, 3221,
-  3227, 3236, 3242, 3267, 3273, 3282, 3288, 3299,
-  3305, 3314, 3320, 3340, 3346, 3355, 3361, 3372,
-  3378, 3387, 3393, 3257, 3263, 3272, 3278, 3289,
-  3295, 3304, 3310, 3330, 3336, 3345, 3351, 3362,
-  3368, 3377, 3383, 3408, 3414, 3423, 3429, 3440,
-  3446, 3455, 3461, 3481, 3487, 3496, 3502, 3513,
-  3519, 3528, 3534, 3557, 3563, 3572, 3578, 3589,
-  3595, 3604, 3610, 3630, 3636, 3645, 3651, 3662,
-  3668, 3677, 3683, 3708, 3714, 3723, 3729, 3740,
-  3746, 3755, 3761, 3781, 3787, 3796, 3802, 3813,
-  3819, 3828, 3834, 3629, 3635, 3644, 3650, 3661,
-  3667, 3676, 3682, 3702, 3708, 3717, 3723, 3734,
-  3740, 3749, 3755, 3780, 3786, 3795, 3801, 3812,
-  3818, 3827, 3833, 3853, 3859, 3868, 3874, 3885,
-  3891, 3900, 3906, 3929, 3935, 3944, 3950, 3961,
-  3967, 3976, 3982, 4002, 4008, 4017, 4023, 4034,
-  4040, 4049, 4055, 4080, 4086, 4095, 4101, 4112,
-  4118, 4127, 4133, 4153, 4159, 4168, 4174, 4185,
-  4191, 4200, 4206, 4070, 4076, 4085, 4091, 4102,
-  4108, 4117, 4123, 4143, 4149, 4158, 4164, 4175,
-  4181, 4190, 4196, 4221, 4227, 4236, 4242, 4253,
-  4259, 4268, 4274, 4294, 4300, 4309, 4315, 4326,
-  4332, 4341, 4347, 4370, 4376, 4385, 4391, 4402,
-  4408, 4417, 4423, 4443, 4449, 4458, 4464, 4475,
-  4481, 4490, 4496, 4521, 4527, 4536, 4542, 4553,
-  4559, 4568, 4574, 4594, 4600, 4609, 4615, 4626,
-  4632, 4641, 4647, 3515, 3521, 3530, 3536, 3547,
-  3553, 3562, 3568, 3588, 3594, 3603, 3609, 3620,
-  3626, 3635, 3641, 3666, 3672, 3681, 3687, 3698,
-  3704, 3713, 3719, 3739, 3745, 3754, 3760, 3771,
-  3777, 3786, 3792, 3815, 3821, 3830, 3836, 3847,
-  3853, 3862, 3868, 3888, 3894, 3903, 3909, 3920,
-  3926, 3935, 3941, 3966, 3972, 3981, 3987, 3998,
-  4004, 4013, 4019, 4039, 4045, 4054, 4060, 4071,
-  4077, 4086, 4092, 3956, 3962, 3971, 3977, 3988,
-  3994, 4003, 4009, 4029, 4035, 4044, 4050, 4061,
-  4067, 4076, 4082, 4107, 4113, 4122, 4128, 4139,
-  4145, 4154, 4160, 4180, 4186, 4195, 4201, 4212,
-  4218, 4227, 4233, 4256, 4262, 4271, 4277, 4288,
-  4294, 4303, 4309, 4329, 4335, 4344, 4350, 4361,
-  4367, 4376, 4382, 4407, 4413, 4422, 4428, 4439,
-  4445, 4454, 4460, 4480, 4486, 4495, 4501, 4512,
-  4518, 4527, 4533, 4328, 4334, 4343, 4349, 4360,
-  4366, 4375, 4381, 4401, 4407, 4416, 4422, 4433,
-  4439, 4448, 4454, 4479, 4485, 4494, 4500, 4511,
-  4517, 4526, 4532, 4552, 4558, 4567, 4573, 4584,
-  4590, 4599, 4605, 4628, 4634, 4643, 4649, 4660,
-  4666, 4675, 4681, 4701, 4707, 4716, 4722, 4733,
-  4739, 4748, 4754, 4779, 4785, 4794, 4800, 4811,
-  4817, 4826, 4832, 4852, 4858, 4867, 4873, 4884,
-  4890, 4899, 4905, 4769, 4775, 4784, 4790, 4801,
-  4807, 4816, 4822, 4842, 4848, 4857, 4863, 4874,
-  4880, 4889, 4895, 4920, 4926, 4935, 4941, 4952,
-  4958, 4967, 4973, 4993, 4999, 5008, 5014, 5025,
-  5031, 5040, 5046, 5069, 5075, 5084, 5090, 5101,
-  5107, 5116, 5122, 5142, 5148, 5157, 5163, 5174,
-  5180, 5189, 5195, 5220, 5226, 5235, 5241, 5252,
-  5258, 5267, 5273, 5293, 5299, 5308, 5314, 5325,
-  5331, 5340, 5346, 4604, 4610, 4619, 4625, 4636,
-  4642, 4651, 4657, 4677, 4683, 4692, 4698, 4709,
-  4715, 4724, 4730, 4755, 4761, 4770, 4776, 4787,
-  4793, 4802, 4808, 4828, 4834, 4843, 4849, 4860,
-  4866, 4875, 4881, 4904, 4910, 4919, 4925, 4936,
-  4942, 4951, 4957, 4977, 4983, 4992, 4998, 5009,
-  5015, 5024, 5030, 5055, 5061, 5070, 5076, 5087,
-  5093, 5102, 5108, 5128, 5134, 5143, 5149, 5160,
-  5166, 5175, 5181, 5045, 5051, 5060, 5066, 5077,
-  5083, 5092, 5098, 5118, 5124, 5133, 5139, 5150,
-  5156, 5165, 5171, 5196, 5202, 5211, 5217, 5228,
-  5234, 5243, 5249, 5269, 5275, 5284, 5290, 5301,
-  5307, 5316, 5322, 5345, 5351, 5360, 5366, 5377,
-  5383, 5392, 5398, 5418, 5424, 5433, 5439, 5450,
-  5456, 5465, 5471, 5496, 5502, 5511, 5517, 5528,
-  5534, 5543, 5549, 5569, 5575, 5584, 5590, 5601,
-  5607, 5616, 5622, 5417, 5423, 5432, 5438, 5449,
-  5455, 5464, 5470, 5490, 5496, 5505, 5511, 5522,
-  5528, 5537, 5543, 5568, 5574, 5583, 5589, 5600,
-  5606, 5615, 5621, 5641, 5647, 5656, 5662, 5673,
-  5679, 5688, 5694, 5717, 5723, 5732, 5738, 5749,
-  5755, 5764, 5770, 5790, 5796, 5805, 5811, 5822,
-  5828, 5837, 5843, 5868, 5874, 5883, 5889, 5900,
-  5906, 5915, 5921, 5941, 5947, 5956, 5962, 5973,
-  5979, 5988, 5994, 5858, 5864, 5873, 5879, 5890,
-  5896, 5905, 5911, 5931, 5937, 5946, 5952, 5963,
-  5969, 5978, 5984, 6009, 6015, 6024, 6030, 6041,
-  6047, 6056, 6062, 6082, 6088, 6097, 6103, 6114,
-  6120, 6129, 6135, 6158, 6164, 6173, 6179, 6190,
-  6196, 6205, 6211, 6231, 6237, 6246, 6252, 6263,
-  6269, 6278, 6284, 6309, 6315, 6324, 6330, 6341,
-  6347, 6356, 6362, 6382, 6388, 6397, 6403, 6414,
-  6420, 6429, 6435, 3515, 3521, 3530, 3536, 3547,
-  3553, 3562, 3568, 3588, 3594, 3603, 3609, 3620,
-  3626, 3635, 3641, 3666, 3672, 3681, 3687, 3698,
-  3704, 3713, 3719, 3739, 3745, 3754, 3760, 3771,
-  3777, 3786, 3792, 3815, 3821, 3830, 3836, 3847,
-  3853, 3862, 3868, 3888, 3894, 3903, 3909, 3920,
-  3926, 3935, 3941, 3966, 3972, 3981, 3987, 3998,
-  4004, 4013, 4019, 4039, 4045, 4054, 4060, 4071,
-  4077, 4086, 4092, 3956, 3962, 3971, 3977, 3988,
-  3994, 4003, 4009, 4029, 4035, 4044, 4050, 4061,
-  4067, 4076, 4082, 4107, 4113, 4122, 4128, 4139,
-  4145, 4154, 4160, 4180, 4186, 4195, 4201, 4212,
-  4218, 4227, 4233, 4256, 4262, 4271, 4277, 4288,
-  4294, 4303, 4309, 4329, 4335, 4344, 4350, 4361,
-  4367, 4376, 4382, 4407, 4413, 4422, 4428, 4439,
-  4445, 4454, 4460, 4480, 4486, 4495, 4501, 4512,
-  4518, 4527, 4533, 4328, 4334, 4343, 4349, 4360,
-  4366, 4375, 4381, 4401, 4407, 4416, 4422, 4433,
-  4439, 4448, 4454, 4479, 4485, 4494, 4500, 4511,
-  4517, 4526, 4532, 4552, 4558, 4567, 4573, 4584,
-  4590, 4599, 4605, 4628, 4634, 4643, 4649, 4660,
-  4666, 4675, 4681, 4701, 4707, 4716, 4722, 4733,
-  4739, 4748, 4754, 4779, 4785, 4794, 4800, 4811,
-  4817, 4826, 4832, 4852, 4858, 4867, 4873, 4884,
-  4890, 4899, 4905, 4769, 4775, 4784, 4790, 4801,
-  4807, 4816, 4822, 4842, 4848, 4857, 4863, 4874,
-  4880, 4889, 4895, 4920, 4926, 4935, 4941, 4952,
-  4958, 4967, 4973, 4993, 4999, 5008, 5014, 5025,
-  5031, 5040, 5046, 5069, 5075, 5084, 5090, 5101,
-  5107, 5116, 5122, 5142, 5148, 5157, 5163, 5174,
-  5180, 5189, 5195, 5220, 5226, 5235, 5241, 5252,
-  5258, 5267, 5273, 5293, 5299, 5308, 5314, 5325,
-  5331, 5340, 5346, 4604, 4610, 4619, 4625, 4636,
-  4642, 4651, 4657, 4677, 4683, 4692, 4698, 4709,
-  4715, 4724, 4730, 4755, 4761, 4770, 4776, 4787,
-  4793, 4802, 4808, 4828, 4834, 4843, 4849, 4860,
-  4866, 4875, 4881, 4904, 4910, 4919, 4925, 4936,
-  4942, 4951, 4957, 4977, 4983, 4992, 4998, 5009,
-  5015, 5024, 5030, 5055, 5061, 5070, 5076, 5087,
-  5093, 5102, 5108, 5128, 5134, 5143, 5149, 5160,
-  5166, 5175, 5181, 5045, 5051, 5060, 5066, 5077,
-  5083, 5092, 5098, 5118, 5124, 5133, 5139, 5150,
-  5156, 5165, 5171, 5196, 5202, 5211, 5217, 5228,
-  5234, 5243, 5249, 5269, 5275, 5284, 5290, 5301,
-  5307, 5316, 5322, 5345, 5351, 5360, 5366, 5377,
-  5383, 5392, 5398, 5418, 5424, 5433, 5439, 5450,
-  5456, 5465, 5471, 5496, 5502, 5511, 5517, 5528,
-  5534, 5543, 5549, 5569, 5575, 5584, 5590, 5601,
-  5607, 5616, 5622, 5417, 5423, 5432, 5438, 5449,
-  5455, 5464, 5470, 5490, 5496, 5505, 5511, 5522,
-  5528, 5537, 5543, 5568, 5574, 5583, 5589, 5600,
-  5606, 5615, 5621, 5641, 5647, 5656, 5662, 5673,
-  5679, 5688, 5694, 5717, 5723, 5732, 5738, 5749,
-  5755, 5764, 5770, 5790, 5796, 5805, 5811, 5822,
-  5828, 5837, 5843, 5868, 5874, 5883, 5889, 5900,
-  5906, 5915, 5921, 5941, 5947, 5956, 5962, 5973,
-  5979, 5988, 5994, 5858, 5864, 5873, 5879, 5890,
-  5896, 5905, 5911, 5931, 5937, 5946, 5952, 5963,
-  5969, 5978, 5984, 6009, 6015, 6024, 6030, 6041,
-  6047, 6056, 6062, 6082, 6088, 6097, 6103, 6114,
-  6120, 6129, 6135, 6158, 6164, 6173, 6179, 6190,
-  6196, 6205, 6211, 6231, 6237, 6246, 6252, 6263,
-  6269, 6278, 6284, 6309, 6315, 6324, 6330, 6341,
-  6347, 6356, 6362, 6382, 6388, 6397, 6403, 6414,
-  6420, 6429, 6435, 5303, 5309, 5318, 5324, 5335,
-  5341, 5350, 5356, 5376, 5382, 5391, 5397, 5408,
-  5414, 5423, 5429, 5454, 5460, 5469, 5475, 5486,
-  5492, 5501, 5507, 5527, 5533, 5542, 5548, 5559,
-  5565, 5574, 5580, 5603, 5609, 5618, 5624, 5635,
-  5641, 5650, 5656, 5676, 5682, 5691, 5697, 5708,
-  5714, 5723, 5729, 5754, 5760, 5769, 5775, 5786,
-  5792, 5801, 5807, 5827, 5833, 5842, 5848, 5859,
-  5865, 5874, 5880, 5744, 5750, 5759, 5765, 5776,
-  5782, 5791, 5797, 5817, 5823, 5832, 5838, 5849,
-  5855, 5864, 5870, 5895, 5901, 5910, 5916, 5927,
-  5933, 5942, 5948, 5968, 5974, 5983, 5989, 6000,
-  6006, 6015, 6021, 6044, 6050, 6059, 6065, 6076,
-  6082, 6091, 6097, 6117, 6123, 6132, 6138, 6149,
-  6155, 6164, 6170, 6195, 6201, 6210, 6216, 6227,
-  6233, 6242, 6248, 6268, 6274, 6283, 6289, 6300,
-  6306, 6315, 6321, 6116, 6122, 6131, 6137, 6148,
-  6154, 6163, 6169, 6189, 6195, 6204, 6210, 6221,
-  6227, 6236, 6242, 6267, 6273, 6282, 6288, 6299,
-  6305, 6314, 6320, 6340, 6346, 6355, 6361, 6372,
-  6378, 6387, 6393, 6416, 6422, 6431, 6437, 6448,
-  6454, 6463, 6469, 6489, 6495, 6504, 6510, 6521,
-  6527, 6536, 6542, 6567, 6573, 6582, 6588, 6599,
-  6605, 6614, 6620, 6640, 6646, 6655, 6661, 6672,
-  6678, 6687, 6693, 6557, 6563, 6572, 6578, 6589,
-  6595, 6604, 6610, 6630, 6636, 6645, 6651, 6662,
-  6668, 6677, 6683, 6708, 6714, 6723, 6729, 6740,
-  6746, 6755, 6761, 6781, 6787, 6796, 6802, 6813,
-  6819, 6828, 6834, 6857, 6863, 6872, 6878, 6889,
-  6895, 6904, 6910, 6930, 6936, 6945, 6951, 6962,
-  6968, 6977, 6983, 7008, 7014, 7023, 7029, 7040,
-  7046, 7055, 7061, 7081, 7087, 7096, 7102, 7113,
-  7119, 7128, 7134, 6392, 6398, 6407, 6413, 6424,
-  6430, 6439, 6445, 6465, 6471, 6480, 6486, 6497,
-  6503, 6512, 6518, 6543, 6549, 6558, 6564, 6575,
-  6581, 6590, 6596, 6616, 6622, 6631, 6637, 6648,
-  6654, 6663, 6669, 6692, 6698, 6707, 6713, 6724,
-  6730, 6739, 6745, 6765, 6771, 6780, 6786, 6797,
-  6803, 6812, 6818, 6843, 6849, 6858, 6864, 6875,
-  6881, 6890, 6896, 6916, 6922, 6931, 6937, 6948,
-  6954, 6963, 6969, 6833, 6839, 6848, 6854, 6865,
-  6871, 6880, 6886, 6906, 6912, 6921, 6927, 6938,
-  6944, 6953, 6959, 6984, 6990, 6999, 7005, 7016,
-  7022, 7031, 7037, 7057, 7063, 7072, 7078, 7089,
-  7095, 7104, 7110, 7133, 7139, 7148, 7154, 7165,
-  7171, 7180, 7186, 7206, 7212, 7221, 7227, 7238,
-  7244, 7253, 7259, 7284, 7290, 7299, 7305, 7316,
-  7322, 7331, 7337, 7357, 7363, 7372, 7378, 7389,
-  7395, 7404, 7410, 7205, 7211, 7220, 7226, 7237,
-  7243, 7252, 7258, 7278, 7284, 7293, 7299, 7310,
-  7316, 7325, 7331, 7356, 7362, 7371, 7377, 7388,
-  7394, 7403, 7409, 7429, 7435, 7444, 7450, 7461,
-  7467, 7476, 7482, 7505, 7511, 7520, 7526, 7537,
-  7543, 7552, 7558, 7578, 7584, 7593, 7599, 7610,
-  7616, 7625, 7631, 7656, 7662, 7671, 7677, 7688,
-  7694, 7703, 7709, 7729, 7735, 7744, 7750, 7761
-};
-
 static int VariableLevelCost(int level, const uint8_t probas[NUM_PROBAS]) {
   int pattern = VP8LevelCodes[level - 1][0];
   int bits = VP8LevelCodes[level - 1][1];
@@ -352,19 +57,21 @@ static int VariableLevelCost(int level, const uint8_t probas[NUM_PROBAS]) {
 //------------------------------------------------------------------------------
 // Pre-calc level costs once for all
 
-void VP8CalculateLevelCosts(VP8Proba* const proba) {
+void VP8CalculateLevelCosts(VP8EncProba* const proba) {
   int ctype, band, ctx;
 
   if (!proba->dirty_) return;  // nothing to do.
 
   for (ctype = 0; ctype < NUM_TYPES; ++ctype) {
+    int n;
     for (band = 0; band < NUM_BANDS; ++band) {
-      for(ctx = 0; ctx < NUM_CTX; ++ctx) {
+      for (ctx = 0; ctx < NUM_CTX; ++ctx) {
         const uint8_t* const p = proba->coeffs_[ctype][band][ctx];
         uint16_t* const table = proba->level_cost_[ctype][band][ctx];
-        const int cost_base = VP8BitCost(1, p[1]);
+        const int cost0 = (ctx > 0) ? VP8BitCost(1, p[0]) : 0;
+        const int cost_base = VP8BitCost(1, p[1]) + cost0;
         int v;
-        table[0] = VP8BitCost(0, p[1]);
+        table[0] = VP8BitCost(0, p[1]) + cost0;
         for (v = 1; v <= MAX_VARIABLE_LEVEL; ++v) {
           table[v] = cost_base + VariableLevelCost(v, p);
         }
@@ -372,6 +79,12 @@ void VP8CalculateLevelCosts(VP8Proba* const proba) {
         // actually constant.
       }
     }
+    for (n = 0; n < 16; ++n) {    // replicate bands. We don't need to sentinel.
+      for (ctx = 0; ctx < NUM_CTX; ++ctx) {
+        proba->remapped_costs_[ctype][n][ctx] =
+            proba->level_cost_[ctype][VP8EncBands[n]][ctx];
+      }
+    }
   }
   proba->dirty_ = 0;
 }
@@ -385,110 +98,257 @@ const uint16_t VP8FixedCostsUV[4] = { 302, 984, 439, 642 };
 // note: these values include the fixed VP8BitCost(1, 145) mode selection cost.
 const uint16_t VP8FixedCostsI16[4] = { 663, 919, 872, 919 };
 const uint16_t VP8FixedCostsI4[NUM_BMODES][NUM_BMODES][NUM_BMODES] = {
-  { {  251, 1362, 1934, 2085, 2314, 2230, 1839, 1988, 2437, 2348 },
-    {  403,  680, 1507, 1519, 2060, 2005, 1992, 1914, 1924, 1733 },
-    {  353, 1121,  973, 1895, 2060, 1787, 1671, 1516, 2012, 1868 },
-    {  770,  852, 1581,  632, 1393, 1780, 1823, 1936, 1074, 1218 },
-    {  510, 1270, 1467, 1319,  847, 1279, 1792, 2094, 1080, 1353 },
-    {  488, 1322,  918, 1573, 1300,  883, 1814, 1752, 1756, 1502 },
-    {  425,  992, 1820, 1514, 1843, 2440,  937, 1771, 1924, 1129 },
-    {  363, 1248, 1257, 1970, 2194, 2385, 1569,  953, 1951, 1601 },
-    {  723, 1257, 1631,  964,  963, 1508, 1697, 1824,  671, 1418 },
-    {  635, 1038, 1573,  930, 1673, 1413, 1410, 1687, 1410,  749 } },
-  { {  451,  613, 1345, 1702, 1870, 1716, 1728, 1766, 2190, 2310 },
-    {  678,  453, 1171, 1443, 1925, 1831, 2045, 1781, 1887, 1602 },
-    {  711,  666,  674, 1718, 1910, 1493, 1775, 1193, 2325, 2325 },
-    {  883,  854, 1583,  542, 1800, 1878, 1664, 2149, 1207, 1087 },
-    {  669,  994, 1248, 1122,  949, 1179, 1376, 1729, 1070, 1244 },
-    {  715, 1026,  715, 1350, 1430,  930, 1717, 1296, 1479, 1479 },
-    {  544,  841, 1656, 1450, 2094, 3883, 1010, 1759, 2076,  809 },
-    {  610,  855,  957, 1553, 2067, 1561, 1704,  824, 2066, 1226 },
-    {  833,  960, 1416,  819, 1277, 1619, 1501, 1617,  757, 1182 },
-    {  711,  964, 1252,  879, 1441, 1828, 1508, 1636, 1594,  734 } },
-  { {  605,  764,  734, 1713, 1747, 1192, 1819, 1353, 1877, 2392 },
-    {  866,  641,  586, 1622, 2072, 1431, 1888, 1346, 2189, 1764 },
-    {  901,  851,  456, 2165, 2281, 1405, 1739, 1193, 2183, 2443 },
-    {  770, 1045,  952, 1078, 1342, 1191, 1436, 1063, 1303,  995 },
-    {  901, 1086,  727, 1170,  884, 1105, 1267, 1401, 1739, 1337 },
-    {  951, 1162,  595, 1488, 1388,  703, 1790, 1366, 2057, 1724 },
-    {  534,  986, 1273, 1987, 3273, 1485, 1024, 1399, 1583,  866 },
-    {  699, 1182,  695, 1978, 1726, 1986, 1326,  714, 1750, 1672 },
-    {  951, 1217, 1209,  920, 1062, 1441, 1548,  999,  952,  932 },
-    {  733, 1284,  784, 1256, 1557, 1098, 1257, 1357, 1414,  908 } },
-  { {  316, 1075, 1653, 1220, 2145, 2051, 1730, 2131, 1884, 1790 },
-    {  745,  516, 1404,  894, 1599, 2375, 2013, 2105, 1475, 1381 },
-    {  516,  729, 1088, 1319, 1637, 3426, 1636, 1275, 1531, 1453 },
-    {  894,  943, 2138,  468, 1704, 2259, 2069, 1763, 1266, 1158 },
-    {  605, 1025, 1235,  871, 1170, 1767, 1493, 1500, 1104, 1258 },
-    {  739,  826, 1207, 1151, 1412,  846, 1305, 2726, 1014, 1569 },
-    {  558,  825, 1820, 1398, 3344, 1556, 1218, 1550, 1228,  878 },
-    {  429,  951, 1089, 1816, 3861, 3861, 1556,  969, 1568, 1828 },
-    {  883,  961, 1752,  769, 1468, 1810, 2081, 2346,  613, 1298 },
-    {  803,  895, 1372,  641, 1303, 1708, 1686, 1700, 1306, 1033 } },
-  { {  439, 1267, 1270, 1579,  963, 1193, 1723, 1729, 1198, 1993 },
-    {  705,  725, 1029, 1153, 1176, 1103, 1821, 1567, 1259, 1574 },
-    {  723,  859,  802, 1253,  972, 1202, 1407, 1665, 1520, 1674 },
-    {  894,  960, 1254,  887, 1052, 1607, 1344, 1349,  865, 1150 },
-    {  833, 1312, 1337, 1205,  572, 1288, 1414, 1529, 1088, 1430 },
-    {  842, 1279, 1068, 1861,  862,  688, 1861, 1630, 1039, 1381 },
-    {  766,  938, 1279, 1546, 3338, 1550, 1031, 1542, 1288,  640 },
-    {  715, 1090,  835, 1609, 1100, 1100, 1603, 1019, 1102, 1617 },
-    {  894, 1813, 1500, 1188,  789, 1194, 1491, 1919,  617, 1333 },
-    {  610, 1076, 1644, 1281, 1283,  975, 1179, 1688, 1434,  889 } },
-  { {  544,  971, 1146, 1849, 1221,  740, 1857, 1621, 1683, 2430 },
-    {  723,  705,  961, 1371, 1426,  821, 2081, 2079, 1839, 1380 },
-    {  783,  857,  703, 2145, 1419,  814, 1791, 1310, 1609, 2206 },
-    {  997, 1000, 1153,  792, 1229, 1162, 1810, 1418,  942,  979 },
-    {  901, 1226,  883, 1289,  793,  715, 1904, 1649, 1319, 3108 },
-    {  979, 1478,  782, 2216, 1454,  455, 3092, 1591, 1997, 1664 },
-    {  663, 1110, 1504, 1114, 1522, 3311,  676, 1522, 1530, 1024 },
-    {  605, 1138, 1153, 1314, 1569, 1315, 1157,  804, 1574, 1320 },
-    {  770, 1216, 1218, 1227,  869, 1384, 1232, 1375,  834, 1239 },
-    {  775, 1007,  843, 1216, 1225, 1074, 2527, 1479, 1149,  975 } },
-  { {  477,  817, 1309, 1439, 1708, 1454, 1159, 1241, 1945, 1672 },
-    {  577,  796, 1112, 1271, 1618, 1458, 1087, 1345, 1831, 1265 },
-    {  663,  776,  753, 1940, 1690, 1690, 1227, 1097, 3149, 1361 },
-    {  766, 1299, 1744, 1161, 1565, 1106, 1045, 1230, 1232,  707 },
-    {  915, 1026, 1404, 1182, 1184,  851, 1428, 2425, 1043,  789 },
-    {  883, 1456,  790, 1082, 1086,  985, 1083, 1484, 1238, 1160 },
-    {  507, 1345, 2261, 1995, 1847, 3636,  653, 1761, 2287,  933 },
-    {  553, 1193, 1470, 2057, 2059, 2059,  833,  779, 2058, 1263 },
-    {  766, 1275, 1515, 1039,  957, 1554, 1286, 1540, 1289,  705 },
-    {  499, 1378, 1496, 1385, 1850, 1850, 1044, 2465, 1515,  720 } },
-  { {  553,  930,  978, 2077, 1968, 1481, 1457,  761, 1957, 2362 },
-    {  694,  864,  905, 1720, 1670, 1621, 1429,  718, 2125, 1477 },
-    {  699,  968,  658, 3190, 2024, 1479, 1865,  750, 2060, 2320 },
-    {  733, 1308, 1296, 1062, 1576, 1322, 1062, 1112, 1172,  816 },
-    {  920,  927, 1052,  939,  947, 1156, 1152, 1073, 3056, 1268 },
-    {  723, 1534,  711, 1547, 1294,  892, 1553,  928, 1815, 1561 },
-    {  663, 1366, 1583, 2111, 1712, 3501,  522, 1155, 2130, 1133 },
-    {  614, 1731, 1188, 2343, 1944, 3733, 1287,  487, 3546, 1758 },
-    {  770, 1585, 1312,  826,  884, 2673, 1185, 1006, 1195, 1195 },
-    {  758, 1333, 1273, 1023, 1621, 1162, 1351,  833, 1479,  862 } },
-  { {  376, 1193, 1446, 1149, 1545, 1577, 1870, 1789, 1175, 1823 },
-    {  803,  633, 1136, 1058, 1350, 1323, 1598, 2247, 1072, 1252 },
-    {  614, 1048,  943,  981, 1152, 1869, 1461, 1020, 1618, 1618 },
-    { 1107, 1085, 1282,  592, 1779, 1933, 1648, 2403,  691, 1246 },
-    {  851, 1309, 1223, 1243,  895, 1593, 1792, 2317,  627, 1076 },
-    {  770, 1216, 1030, 1125,  921,  981, 1629, 1131, 1049, 1646 },
-    {  626, 1469, 1456, 1081, 1489, 3278,  981, 1232, 1498,  733 },
-    {  617, 1201,  812, 1220, 1476, 1476, 1478,  970, 1228, 1488 },
-    { 1179, 1393, 1540,  999, 1243, 1503, 1916, 1925,  414, 1614 },
-    {  943, 1088, 1490,  682, 1112, 1372, 1756, 1505,  966,  966 } },
-  { {  322, 1142, 1589, 1396, 2144, 1859, 1359, 1925, 2084, 1518 },
-    {  617,  625, 1241, 1234, 2121, 1615, 1524, 1858, 1720, 1004 },
-    {  553,  851,  786, 1299, 1452, 1560, 1372, 1561, 1967, 1713 },
-    {  770,  977, 1396,  568, 1893, 1639, 1540, 2108, 1430, 1013 },
-    {  684, 1120, 1375,  982,  930, 2719, 1638, 1643,  933,  993 },
-    {  553, 1103,  996, 1356, 1361, 1005, 1507, 1761, 1184, 1268 },
-    {  419, 1247, 1537, 1554, 1817, 3606, 1026, 1666, 1829,  923 },
-    {  439, 1139, 1101, 1257, 3710, 1922, 1205, 1040, 1931, 1529 },
-    {  979,  935, 1269,  847, 1202, 1286, 1530, 1535,  827, 1036 },
-    {  516, 1378, 1569, 1110, 1798, 1798, 1198, 2199, 1543,  712 } },
+  { {   40, 1151, 1723, 1874, 2103, 2019, 1628, 1777, 2226, 2137 },
+    {  192,  469, 1296, 1308, 1849, 1794, 1781, 1703, 1713, 1522 },
+    {  142,  910,  762, 1684, 1849, 1576, 1460, 1305, 1801, 1657 },
+    {  559,  641, 1370,  421, 1182, 1569, 1612, 1725,  863, 1007 },
+    {  299, 1059, 1256, 1108,  636, 1068, 1581, 1883,  869, 1142 },
+    {  277, 1111,  707, 1362, 1089,  672, 1603, 1541, 1545, 1291 },
+    {  214,  781, 1609, 1303, 1632, 2229,  726, 1560, 1713,  918 },
+    {  152, 1037, 1046, 1759, 1983, 2174, 1358,  742, 1740, 1390 },
+    {  512, 1046, 1420,  753,  752, 1297, 1486, 1613,  460, 1207 },
+    {  424,  827, 1362,  719, 1462, 1202, 1199, 1476, 1199,  538 } },
+  { {  240,  402, 1134, 1491, 1659, 1505, 1517, 1555, 1979, 2099 },
+    {  467,  242,  960, 1232, 1714, 1620, 1834, 1570, 1676, 1391 },
+    {  500,  455,  463, 1507, 1699, 1282, 1564,  982, 2114, 2114 },
+    {  672,  643, 1372,  331, 1589, 1667, 1453, 1938,  996,  876 },
+    {  458,  783, 1037,  911,  738,  968, 1165, 1518,  859, 1033 },
+    {  504,  815,  504, 1139, 1219,  719, 1506, 1085, 1268, 1268 },
+    {  333,  630, 1445, 1239, 1883, 3672,  799, 1548, 1865,  598 },
+    {  399,  644,  746, 1342, 1856, 1350, 1493,  613, 1855, 1015 },
+    {  622,  749, 1205,  608, 1066, 1408, 1290, 1406,  546,  971 },
+    {  500,  753, 1041,  668, 1230, 1617, 1297, 1425, 1383,  523 } },
+  { {  394,  553,  523, 1502, 1536,  981, 1608, 1142, 1666, 2181 },
+    {  655,  430,  375, 1411, 1861, 1220, 1677, 1135, 1978, 1553 },
+    {  690,  640,  245, 1954, 2070, 1194, 1528,  982, 1972, 2232 },
+    {  559,  834,  741,  867, 1131,  980, 1225,  852, 1092,  784 },
+    {  690,  875,  516,  959,  673,  894, 1056, 1190, 1528, 1126 },
+    {  740,  951,  384, 1277, 1177,  492, 1579, 1155, 1846, 1513 },
+    {  323,  775, 1062, 1776, 3062, 1274,  813, 1188, 1372,  655 },
+    {  488,  971,  484, 1767, 1515, 1775, 1115,  503, 1539, 1461 },
+    {  740, 1006,  998,  709,  851, 1230, 1337,  788,  741,  721 },
+    {  522, 1073,  573, 1045, 1346,  887, 1046, 1146, 1203,  697 } },
+  { {  105,  864, 1442, 1009, 1934, 1840, 1519, 1920, 1673, 1579 },
+    {  534,  305, 1193,  683, 1388, 2164, 1802, 1894, 1264, 1170 },
+    {  305,  518,  877, 1108, 1426, 3215, 1425, 1064, 1320, 1242 },
+    {  683,  732, 1927,  257, 1493, 2048, 1858, 1552, 1055,  947 },
+    {  394,  814, 1024,  660,  959, 1556, 1282, 1289,  893, 1047 },
+    {  528,  615,  996,  940, 1201,  635, 1094, 2515,  803, 1358 },
+    {  347,  614, 1609, 1187, 3133, 1345, 1007, 1339, 1017,  667 },
+    {  218,  740,  878, 1605, 3650, 3650, 1345,  758, 1357, 1617 },
+    {  672,  750, 1541,  558, 1257, 1599, 1870, 2135,  402, 1087 },
+    {  592,  684, 1161,  430, 1092, 1497, 1475, 1489, 1095,  822 } },
+  { {  228, 1056, 1059, 1368,  752,  982, 1512, 1518,  987, 1782 },
+    {  494,  514,  818,  942,  965,  892, 1610, 1356, 1048, 1363 },
+    {  512,  648,  591, 1042,  761,  991, 1196, 1454, 1309, 1463 },
+    {  683,  749, 1043,  676,  841, 1396, 1133, 1138,  654,  939 },
+    {  622, 1101, 1126,  994,  361, 1077, 1203, 1318,  877, 1219 },
+    {  631, 1068,  857, 1650,  651,  477, 1650, 1419,  828, 1170 },
+    {  555,  727, 1068, 1335, 3127, 1339,  820, 1331, 1077,  429 },
+    {  504,  879,  624, 1398,  889,  889, 1392,  808,  891, 1406 },
+    {  683, 1602, 1289,  977,  578,  983, 1280, 1708,  406, 1122 },
+    {  399,  865, 1433, 1070, 1072,  764,  968, 1477, 1223,  678 } },
+  { {  333,  760,  935, 1638, 1010,  529, 1646, 1410, 1472, 2219 },
+    {  512,  494,  750, 1160, 1215,  610, 1870, 1868, 1628, 1169 },
+    {  572,  646,  492, 1934, 1208,  603, 1580, 1099, 1398, 1995 },
+    {  786,  789,  942,  581, 1018,  951, 1599, 1207,  731,  768 },
+    {  690, 1015,  672, 1078,  582,  504, 1693, 1438, 1108, 2897 },
+    {  768, 1267,  571, 2005, 1243,  244, 2881, 1380, 1786, 1453 },
+    {  452,  899, 1293,  903, 1311, 3100,  465, 1311, 1319,  813 },
+    {  394,  927,  942, 1103, 1358, 1104,  946,  593, 1363, 1109 },
+    {  559, 1005, 1007, 1016,  658, 1173, 1021, 1164,  623, 1028 },
+    {  564,  796,  632, 1005, 1014,  863, 2316, 1268,  938,  764 } },
+  { {  266,  606, 1098, 1228, 1497, 1243,  948, 1030, 1734, 1461 },
+    {  366,  585,  901, 1060, 1407, 1247,  876, 1134, 1620, 1054 },
+    {  452,  565,  542, 1729, 1479, 1479, 1016,  886, 2938, 1150 },
+    {  555, 1088, 1533,  950, 1354,  895,  834, 1019, 1021,  496 },
+    {  704,  815, 1193,  971,  973,  640, 1217, 2214,  832,  578 },
+    {  672, 1245,  579,  871,  875,  774,  872, 1273, 1027,  949 },
+    {  296, 1134, 2050, 1784, 1636, 3425,  442, 1550, 2076,  722 },
+    {  342,  982, 1259, 1846, 1848, 1848,  622,  568, 1847, 1052 },
+    {  555, 1064, 1304,  828,  746, 1343, 1075, 1329, 1078,  494 },
+    {  288, 1167, 1285, 1174, 1639, 1639,  833, 2254, 1304,  509 } },
+  { {  342,  719,  767, 1866, 1757, 1270, 1246,  550, 1746, 2151 },
+    {  483,  653,  694, 1509, 1459, 1410, 1218,  507, 1914, 1266 },
+    {  488,  757,  447, 2979, 1813, 1268, 1654,  539, 1849, 2109 },
+    {  522, 1097, 1085,  851, 1365, 1111,  851,  901,  961,  605 },
+    {  709,  716,  841,  728,  736,  945,  941,  862, 2845, 1057 },
+    {  512, 1323,  500, 1336, 1083,  681, 1342,  717, 1604, 1350 },
+    {  452, 1155, 1372, 1900, 1501, 3290,  311,  944, 1919,  922 },
+    {  403, 1520,  977, 2132, 1733, 3522, 1076,  276, 3335, 1547 },
+    {  559, 1374, 1101,  615,  673, 2462,  974,  795,  984,  984 },
+    {  547, 1122, 1062,  812, 1410,  951, 1140,  622, 1268,  651 } },
+  { {  165,  982, 1235,  938, 1334, 1366, 1659, 1578,  964, 1612 },
+    {  592,  422,  925,  847, 1139, 1112, 1387, 2036,  861, 1041 },
+    {  403,  837,  732,  770,  941, 1658, 1250,  809, 1407, 1407 },
+    {  896,  874, 1071,  381, 1568, 1722, 1437, 2192,  480, 1035 },
+    {  640, 1098, 1012, 1032,  684, 1382, 1581, 2106,  416,  865 },
+    {  559, 1005,  819,  914,  710,  770, 1418,  920,  838, 1435 },
+    {  415, 1258, 1245,  870, 1278, 3067,  770, 1021, 1287,  522 },
+    {  406,  990,  601, 1009, 1265, 1265, 1267,  759, 1017, 1277 },
+    {  968, 1182, 1329,  788, 1032, 1292, 1705, 1714,  203, 1403 },
+    {  732,  877, 1279,  471,  901, 1161, 1545, 1294,  755,  755 } },
+  { {  111,  931, 1378, 1185, 1933, 1648, 1148, 1714, 1873, 1307 },
+    {  406,  414, 1030, 1023, 1910, 1404, 1313, 1647, 1509,  793 },
+    {  342,  640,  575, 1088, 1241, 1349, 1161, 1350, 1756, 1502 },
+    {  559,  766, 1185,  357, 1682, 1428, 1329, 1897, 1219,  802 },
+    {  473,  909, 1164,  771,  719, 2508, 1427, 1432,  722,  782 },
+    {  342,  892,  785, 1145, 1150,  794, 1296, 1550,  973, 1057 },
+    {  208, 1036, 1326, 1343, 1606, 3395,  815, 1455, 1618,  712 },
+    {  228,  928,  890, 1046, 3499, 1711,  994,  829, 1720, 1318 },
+    {  768,  724, 1058,  636,  991, 1075, 1319, 1324,  616,  825 },
+    {  305, 1167, 1358,  899, 1587, 1587,  987, 1988, 1332,  501 } }
 };
 
 //------------------------------------------------------------------------------
+// helper functions for residuals struct VP8Residual.
+
+void VP8InitResidual(int first, int coeff_type,
+                     VP8Encoder* const enc, VP8Residual* const res) {
+  res->coeff_type = coeff_type;
+  res->prob  = enc->proba_.coeffs_[coeff_type];
+  res->stats = enc->proba_.stats_[coeff_type];
+  res->costs = enc->proba_.remapped_costs_[coeff_type];
+  res->first = first;
+}
+
+//------------------------------------------------------------------------------
+// Mode costs
+
+int VP8GetCostLuma4(VP8EncIterator* const it, const int16_t levels[16]) {
+  const int x = (it->i4_ & 3), y = (it->i4_ >> 2);
+  VP8Residual res;
+  VP8Encoder* const enc = it->enc_;
+  int R = 0;
+  int ctx;
+
+  VP8InitResidual(0, 3, enc, &res);
+  ctx = it->top_nz_[x] + it->left_nz_[y];
+  VP8SetResidualCoeffs(levels, &res);
+  R += VP8GetResidualCost(ctx, &res);
+  return R;
+}
+
+int VP8GetCostLuma16(VP8EncIterator* const it, const VP8ModeScore* const rd) {
+  VP8Residual res;
+  VP8Encoder* const enc = it->enc_;
+  int x, y;
+  int R = 0;
+
+  VP8IteratorNzToBytes(it);   // re-import the non-zero context
+
+  // DC
+  VP8InitResidual(0, 1, enc, &res);
+  VP8SetResidualCoeffs(rd->y_dc_levels, &res);
+  R += VP8GetResidualCost(it->top_nz_[8] + it->left_nz_[8], &res);
+
+  // AC
+  VP8InitResidual(1, 0, enc, &res);
+  for (y = 0; y < 4; ++y) {
+    for (x = 0; x < 4; ++x) {
+      const int ctx = it->top_nz_[x] + it->left_nz_[y];
+      VP8SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
+      R += VP8GetResidualCost(ctx, &res);
+      it->top_nz_[x] = it->left_nz_[y] = (res.last >= 0);
+    }
+  }
+  return R;
+}
+
+int VP8GetCostUV(VP8EncIterator* const it, const VP8ModeScore* const rd) {
+  VP8Residual res;
+  VP8Encoder* const enc = it->enc_;
+  int ch, x, y;
+  int R = 0;
+
+  VP8IteratorNzToBytes(it);  // re-import the non-zero context
+
+  VP8InitResidual(0, 2, enc, &res);
+  for (ch = 0; ch <= 2; ch += 2) {
+    for (y = 0; y < 2; ++y) {
+      for (x = 0; x < 2; ++x) {
+        const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
+        VP8SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
+        R += VP8GetResidualCost(ctx, &res);
+        it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] = (res.last >= 0);
+      }
+    }
+  }
+  return R;
+}
+
+
+//------------------------------------------------------------------------------
+// Recording of token probabilities.
+
+// Record proba context used
+static int Record(int bit, proba_t* const stats) {
+  proba_t p = *stats;
+  if (p >= 0xffff0000u) {               // an overflow is inbound.
+    p = ((p + 1u) >> 1) & 0x7fff7fffu;  // -> divide the stats by 2.
+  }
+  // record bit count (lower 16 bits) and increment total count (upper 16 bits).
+  p += 0x00010000u + bit;
+  *stats = p;
+  return bit;
+}
+
+// We keep the table-free variant around for reference, in case.
+#define USE_LEVEL_CODE_TABLE
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
+// Simulate block coding, but only record statistics.
+// Note: no need to record the fixed probas.
+int VP8RecordCoeffs(int ctx, const VP8Residual* const res) {
+  int n = res->first;
+  // should be stats[VP8EncBands[n]], but it's equivalent for n=0 or 1
+  proba_t* s = res->stats[n][ctx];
+  if (res->last  < 0) {
+    Record(0, s + 0);
+    return 0;
+  }
+  while (n <= res->last) {
+    int v;
+    Record(1, s + 0);  // order of record doesn't matter
+    while ((v = res->coeffs[n++]) == 0) {
+      Record(0, s + 1);
+      s = res->stats[VP8EncBands[n]][0];
+    }
+    Record(1, s + 1);
+    if (!Record(2u < (unsigned int)(v + 1), s + 2)) {  // v = -1 or 1
+      s = res->stats[VP8EncBands[n]][1];
+    } else {
+      v = abs(v);
+#if !defined(USE_LEVEL_CODE_TABLE)
+      if (!Record(v > 4, s + 3)) {
+        if (Record(v != 2, s + 4))
+          Record(v == 4, s + 5);
+      } else if (!Record(v > 10, s + 6)) {
+        Record(v > 6, s + 7);
+      } else if (!Record((v >= 3 + (8 << 2)), s + 8)) {
+        Record((v >= 3 + (8 << 1)), s + 9);
+      } else {
+        Record((v >= 3 + (8 << 3)), s + 10);
+      }
+#else
+      if (v > MAX_VARIABLE_LEVEL) {
+        v = MAX_VARIABLE_LEVEL;
+      }
+
+      {
+        const int bits = VP8LevelCodes[v - 1][1];
+        int pattern = VP8LevelCodes[v - 1][0];
+        int i;
+        for (i = 0; (pattern >>= 1) != 0; ++i) {
+          const int mask = 2 << i;
+          if (pattern & 1) Record(!!(bits & mask), s + 3 + i);
+        }
+      }
 #endif
+      s = res->stats[VP8EncBands[n]][2];
+    }
+  }
+  if (n < 16) Record(0, s + 0);
+  return 1;
+}
+
+//------------------------------------------------------------------------------
diff --git a/drivers/webp/enc/cost.h b/drivers/webp/enc/cost.h
index 09b75b699d..20960d6d74 100644
--- a/drivers/webp/enc/cost.h
+++ b/drivers/webp/enc/cost.h
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Cost tables for level and modes.
@@ -12,14 +14,32 @@
 #ifndef WEBP_ENC_COST_H_
 #define WEBP_ENC_COST_H_
 
+#include <assert.h>
+#include <stdlib.h>
 #include "./vp8enci.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
-extern const uint16_t VP8LevelFixedCosts[2048];   // approximate cost per level
-extern const uint16_t VP8EntropyCost[256];        // 8bit fixed-point log(p)
+// On-the-fly info about the current set of residuals. Handy to avoid
+// passing zillions of params.
+typedef struct VP8Residual VP8Residual;
+struct VP8Residual {
+  int first;
+  int last;
+  const int16_t* coeffs;
+
+  int coeff_type;
+  ProbaArray*   prob;
+  StatsArray*   stats;
+  CostArrayPtr  costs;
+};
+
+void VP8InitResidual(int first, int coeff_type,
+                     VP8Encoder* const enc, VP8Residual* const res);
+
+int VP8RecordCoeffs(int ctx, const VP8Residual* const res);
 
 // Cost of coding one event with probability 'proba'.
 static WEBP_INLINE int VP8BitCost(int bit, uint8_t proba) {
@@ -28,7 +48,7 @@ static WEBP_INLINE int VP8BitCost(int bit, uint8_t proba) {
 
 // Level cost calculations
 extern const uint16_t VP8LevelCodes[MAX_VARIABLE_LEVEL][2];
-void VP8CalculateLevelCosts(VP8Proba* const proba);
+void VP8CalculateLevelCosts(VP8EncProba* const proba);
 static WEBP_INLINE int VP8LevelCost(const uint16_t* const table, int level) {
   return VP8LevelFixedCosts[level]
        + table[(level > MAX_VARIABLE_LEVEL) ? MAX_VARIABLE_LEVEL : level];
@@ -41,7 +61,7 @@ extern const uint16_t VP8FixedCostsI4[NUM_BMODES][NUM_BMODES][NUM_BMODES];
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/drivers/webp/enc/filter.c b/drivers/webp/enc/filter.c
index 7fb78a3949..1a4dd947fb 100644
--- a/drivers/webp/enc/filter.c
+++ b/drivers/webp/enc/filter.c
@@ -1,194 +1,68 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Selecting filter level
 //
 // Author: somnath@google.com (Somnath Banerjee)
 
+#include <assert.h>
 #include "./vp8enci.h"
-
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
-// NOTE: clip1, tables and InitTables are repeated entries of dsp.c
-static uint8_t abs0[255 + 255 + 1];     // abs(i)
-static uint8_t abs1[255 + 255 + 1];     // abs(i)>>1
-static int8_t sclip1[1020 + 1020 + 1];  // clips [-1020, 1020] to [-128, 127]
-static int8_t sclip2[112 + 112 + 1];    // clips [-112, 112] to [-16, 15]
-static uint8_t clip1[255 + 510 + 1];    // clips [-255,510] to [0,255]
-
-static int tables_ok = 0;
-
-static void InitTables(void) {
-  if (!tables_ok) {
-    int i;
-    for (i = -255; i <= 255; ++i) {
-      abs0[255 + i] = (i < 0) ? -i : i;
-      abs1[255 + i] = abs0[255 + i] >> 1;
-    }
-    for (i = -1020; i <= 1020; ++i) {
-      sclip1[1020 + i] = (i < -128) ? -128 : (i > 127) ? 127 : i;
-    }
-    for (i = -112; i <= 112; ++i) {
-      sclip2[112 + i] = (i < -16) ? -16 : (i > 15) ? 15 : i;
-    }
-    for (i = -255; i <= 255 + 255; ++i) {
-      clip1[255 + i] = (i < 0) ? 0 : (i > 255) ? 255 : i;
-    }
-    tables_ok = 1;
-  }
-}
-
-//------------------------------------------------------------------------------
-// Edge filtering functions
-
-// 4 pixels in, 2 pixels out
-static WEBP_INLINE void do_filter2(uint8_t* p, int step) {
-  const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
-  const int a = 3 * (q0 - p0) + sclip1[1020 + p1 - q1];
-  const int a1 = sclip2[112 + ((a + 4) >> 3)];
-  const int a2 = sclip2[112 + ((a + 3) >> 3)];
-  p[-step] = clip1[255 + p0 + a2];
-  p[    0] = clip1[255 + q0 - a1];
-}
-
-// 4 pixels in, 4 pixels out
-static WEBP_INLINE void do_filter4(uint8_t* p, int step) {
-  const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
-  const int a = 3 * (q0 - p0);
-  const int a1 = sclip2[112 + ((a + 4) >> 3)];
-  const int a2 = sclip2[112 + ((a + 3) >> 3)];
-  const int a3 = (a1 + 1) >> 1;
-  p[-2*step] = clip1[255 + p1 + a3];
-  p[-  step] = clip1[255 + p0 + a2];
-  p[      0] = clip1[255 + q0 - a1];
-  p[   step] = clip1[255 + q1 - a3];
-}
-
-// high edge-variance
-static WEBP_INLINE int hev(const uint8_t* p, int step, int thresh) {
-  const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
-  return (abs0[255 + p1 - p0] > thresh) || (abs0[255 + q1 - q0] > thresh);
-}
-
-static WEBP_INLINE int needs_filter(const uint8_t* p, int step, int thresh) {
-  const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
-  return (2 * abs0[255 + p0 - q0] + abs1[255 + p1 - q1]) <= thresh;
-}
-
-static WEBP_INLINE int needs_filter2(const uint8_t* p,
-                                     int step, int t, int it) {
-  const int p3 = p[-4*step], p2 = p[-3*step], p1 = p[-2*step], p0 = p[-step];
-  const int q0 = p[0], q1 = p[step], q2 = p[2*step], q3 = p[3*step];
-  if ((2 * abs0[255 + p0 - q0] + abs1[255 + p1 - q1]) > t)
-    return 0;
-  return abs0[255 + p3 - p2] <= it && abs0[255 + p2 - p1] <= it &&
-         abs0[255 + p1 - p0] <= it && abs0[255 + q3 - q2] <= it &&
-         abs0[255 + q2 - q1] <= it && abs0[255 + q1 - q0] <= it;
+#include "../dsp/dsp.h"
+
+// This table gives, for a given sharpness, the filtering strength to be
+// used (at least) in order to filter a given edge step delta.
+// This is constructed by brute force inspection: for all delta, we iterate
+// over all possible filtering strength / thresh until needs_filter() returns
+// true.
+#define MAX_DELTA_SIZE 64
+static const uint8_t kLevelsFromDelta[8][MAX_DELTA_SIZE] = {
+  { 0,   1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
+    16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
+    32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
+    48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63 },
+  { 0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 13, 14, 15, 17, 18,
+    20, 21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42,
+    44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
+  {  0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 13, 14, 16, 17, 19,
+    20, 22, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43,
+    44, 46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
+  {  0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 13, 15, 16, 18, 19,
+    21, 22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43,
+    45, 46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 61, 63, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
+  {  0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 14, 15, 17, 18, 20,
+    21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44,
+    45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
+  {  0,  1,  2,  4,  5,  7,  8,  9, 11, 12, 13, 15, 16, 17, 19, 20,
+    22, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43, 44,
+    46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 63, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
+  {  0,  1,  2,  4,  5,  7,  8,  9, 11, 12, 13, 15, 16, 18, 19, 21,
+    22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43, 45,
+    46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 61, 63, 63, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
+  {  0,  1,  2,  4,  5,  7,  8,  9, 11, 12, 14, 15, 17, 18, 20, 21,
+    23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44, 45,
+    47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63, 63, 63,
+    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 }
+};
+
+int VP8FilterStrengthFromDelta(int sharpness, int delta) {
+  const int pos = (delta < MAX_DELTA_SIZE) ? delta : MAX_DELTA_SIZE - 1;
+  assert(sharpness >= 0 && sharpness <= 7);
+  return kLevelsFromDelta[sharpness][pos];
 }
 
 //------------------------------------------------------------------------------
-// Simple In-loop filtering (Paragraph 15.2)
-
-static void SimpleVFilter16(uint8_t* p, int stride, int thresh) {
-  int i;
-  for (i = 0; i < 16; ++i) {
-    if (needs_filter(p + i, stride, thresh)) {
-      do_filter2(p + i, stride);
-    }
-  }
-}
-
-static void SimpleHFilter16(uint8_t* p, int stride, int thresh) {
-  int i;
-  for (i = 0; i < 16; ++i) {
-    if (needs_filter(p + i * stride, 1, thresh)) {
-      do_filter2(p + i * stride, 1);
-    }
-  }
-}
-
-static void SimpleVFilter16i(uint8_t* p, int stride, int thresh) {
-  int k;
-  for (k = 3; k > 0; --k) {
-    p += 4 * stride;
-    SimpleVFilter16(p, stride, thresh);
-  }
-}
-
-static void SimpleHFilter16i(uint8_t* p, int stride, int thresh) {
-  int k;
-  for (k = 3; k > 0; --k) {
-    p += 4;
-    SimpleHFilter16(p, stride, thresh);
-  }
-}
-
-//------------------------------------------------------------------------------
-// Complex In-loop filtering (Paragraph 15.3)
-
-static WEBP_INLINE void FilterLoop24(uint8_t* p,
-                                     int hstride, int vstride, int size,
-                                     int thresh, int ithresh, int hev_thresh) {
-  while (size-- > 0) {
-    if (needs_filter2(p, hstride, thresh, ithresh)) {
-      if (hev(p, hstride, hev_thresh)) {
-        do_filter2(p, hstride);
-      } else {
-        do_filter4(p, hstride);
-      }
-    }
-    p += vstride;
-  }
-}
-
-// on three inner edges
-static void VFilter16i(uint8_t* p, int stride,
-                       int thresh, int ithresh, int hev_thresh) {
-  int k;
-  for (k = 3; k > 0; --k) {
-    p += 4 * stride;
-    FilterLoop24(p, stride, 1, 16, thresh, ithresh, hev_thresh);
-  }
-}
-
-static void HFilter16i(uint8_t* p, int stride,
-                       int thresh, int ithresh, int hev_thresh) {
-  int k;
-  for (k = 3; k > 0; --k) {
-    p += 4;
-    FilterLoop24(p, 1, stride, 16, thresh, ithresh, hev_thresh);
-  }
-}
-
-static void VFilter8i(uint8_t* u, uint8_t* v, int stride,
-                      int thresh, int ithresh, int hev_thresh) {
-  FilterLoop24(u + 4 * stride, stride, 1, 8, thresh, ithresh, hev_thresh);
-  FilterLoop24(v + 4 * stride, stride, 1, 8, thresh, ithresh, hev_thresh);
-}
-
-static void HFilter8i(uint8_t* u, uint8_t* v, int stride,
-                      int thresh, int ithresh, int hev_thresh) {
-  FilterLoop24(u + 4, 1, stride, 8, thresh, ithresh, hev_thresh);
-  FilterLoop24(v + 4, 1, stride, 8, thresh, ithresh, hev_thresh);
-}
-
-//------------------------------------------------------------------------------
-
-void (*VP8EncVFilter16i)(uint8_t*, int, int, int, int) = VFilter16i;
-void (*VP8EncHFilter16i)(uint8_t*, int, int, int, int) = HFilter16i;
-void (*VP8EncVFilter8i)(uint8_t*, uint8_t*, int, int, int, int) = VFilter8i;
-void (*VP8EncHFilter8i)(uint8_t*, uint8_t*, int, int, int, int) = HFilter8i;
-
-void (*VP8EncSimpleVFilter16i)(uint8_t*, int, int) = SimpleVFilter16i;
-void (*VP8EncSimpleHFilter16i)(uint8_t*, int, int) = SimpleHFilter16i;
-
-//------------------------------------------------------------------------------
 // Paragraph 15.4: compute the inner-edge filtering strength
 
 static int GetILevel(int sharpness, int level) {
@@ -211,22 +85,22 @@ static void DoFilter(const VP8EncIterator* const it, int level) {
   const int ilevel = GetILevel(enc->config_->filter_sharpness, level);
   const int limit = 2 * level + ilevel;
 
-  uint8_t* const y_dst = it->yuv_out2_ + Y_OFF;
-  uint8_t* const u_dst = it->yuv_out2_ + U_OFF;
-  uint8_t* const v_dst = it->yuv_out2_ + V_OFF;
+  uint8_t* const y_dst = it->yuv_out2_ + Y_OFF_ENC;
+  uint8_t* const u_dst = it->yuv_out2_ + U_OFF_ENC;
+  uint8_t* const v_dst = it->yuv_out2_ + V_OFF_ENC;
 
   // copy current block to yuv_out2_
-  memcpy(y_dst, it->yuv_out_, YUV_SIZE * sizeof(uint8_t));
+  memcpy(y_dst, it->yuv_out_, YUV_SIZE_ENC * sizeof(uint8_t));
 
   if (enc->filter_hdr_.simple_ == 1) {   // simple
-    VP8EncSimpleHFilter16i(y_dst, BPS, limit);
-    VP8EncSimpleVFilter16i(y_dst, BPS, limit);
+    VP8SimpleHFilter16i(y_dst, BPS, limit);
+    VP8SimpleVFilter16i(y_dst, BPS, limit);
   } else {    // complex
     const int hev_thresh = (level >= 40) ? 2 : (level >= 15) ? 1 : 0;
-    VP8EncHFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
-    VP8EncHFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
-    VP8EncVFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
-    VP8EncVFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
+    VP8HFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
+    VP8HFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
+    VP8VFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
+    VP8VFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
   }
 }
 
@@ -321,13 +195,16 @@ static double GetMBSSIM(const uint8_t* yuv1, const uint8_t* yuv2) {
   // compute SSIM in a 10 x 10 window
   for (x = 3; x < 13; x++) {
     for (y = 3; y < 13; y++) {
-      VP8SSIMAccumulate(yuv1 + Y_OFF, BPS, yuv2 + Y_OFF, BPS, x, y, 16, 16, &s);
+      VP8SSIMAccumulate(yuv1 + Y_OFF_ENC, BPS, yuv2 + Y_OFF_ENC, BPS,
+                        x, y, 16, 16, &s);
     }
   }
   for (x = 1; x < 7; x++) {
     for (y = 1; y < 7; y++) {
-      VP8SSIMAccumulate(yuv1 + U_OFF, BPS, yuv2 + U_OFF, BPS, x, y, 8, 8, &s);
-      VP8SSIMAccumulate(yuv1 + V_OFF, BPS, yuv2 + V_OFF, BPS, x, y, 8, 8, &s);
+      VP8SSIMAccumulate(yuv1 + U_OFF_ENC, BPS, yuv2 + U_OFF_ENC, BPS,
+                        x, y, 8, 8, &s);
+      VP8SSIMAccumulate(yuv1 + V_OFF_ENC, BPS, yuv2 + V_OFF_ENC, BPS,
+                        x, y, 8, 8, &s);
     }
   }
   return VP8SSIMGet(&s);
@@ -338,28 +215,28 @@ static double GetMBSSIM(const uint8_t* yuv1, const uint8_t* yuv2) {
 // loop filter strength
 
 void VP8InitFilter(VP8EncIterator* const it) {
-  int s, i;
-  if (!it->lf_stats_) return;
-
-  InitTables();
-  for (s = 0; s < NUM_MB_SEGMENTS; s++) {
-    for (i = 0; i < MAX_LF_LEVELS; i++) {
-      (*it->lf_stats_)[s][i] = 0;
+  if (it->lf_stats_ != NULL) {
+    int s, i;
+    for (s = 0; s < NUM_MB_SEGMENTS; s++) {
+      for (i = 0; i < MAX_LF_LEVELS; i++) {
+        (*it->lf_stats_)[s][i] = 0;
+      }
     }
   }
 }
 
 void VP8StoreFilterStats(VP8EncIterator* const it) {
   int d;
+  VP8Encoder* const enc = it->enc_;
   const int s = it->mb_->segment_;
-  const int level0 = it->enc_->dqm_[s].fstrength_;  // TODO: ref_lf_delta[]
+  const int level0 = enc->dqm_[s].fstrength_;  // TODO: ref_lf_delta[]
 
   // explore +/-quant range of values around level0
-  const int delta_min = -it->enc_->dqm_[s].quant_;
-  const int delta_max = it->enc_->dqm_[s].quant_;
+  const int delta_min = -enc->dqm_[s].quant_;
+  const int delta_max = enc->dqm_[s].quant_;
   const int step_size = (delta_max - delta_min >= 4) ? 4 : 1;
 
-  if (!it->lf_stats_) return;
+  if (it->lf_stats_ == NULL) return;
 
   // NOTE: Currently we are applying filter only across the sublock edges
   // There are two reasons for that.
@@ -383,27 +260,40 @@ void VP8StoreFilterStats(VP8EncIterator* const it) {
 }
 
 void VP8AdjustFilterStrength(VP8EncIterator* const it) {
-  int s;
   VP8Encoder* const enc = it->enc_;
-
-  if (!it->lf_stats_) {
-    return;
-  }
-  for (s = 0; s < NUM_MB_SEGMENTS; s++) {
-    int i, best_level = 0;
-    // Improvement over filter level 0 should be at least 1e-5 (relatively)
-    double best_v = 1.00001 * (*it->lf_stats_)[s][0];
-    for (i = 1; i < MAX_LF_LEVELS; i++) {
-      const double v = (*it->lf_stats_)[s][i];
-      if (v > best_v) {
-        best_v = v;
-        best_level = i;
+  if (it->lf_stats_ != NULL) {
+    int s;
+    for (s = 0; s < NUM_MB_SEGMENTS; s++) {
+      int i, best_level = 0;
+      // Improvement over filter level 0 should be at least 1e-5 (relatively)
+      double best_v = 1.00001 * (*it->lf_stats_)[s][0];
+      for (i = 1; i < MAX_LF_LEVELS; i++) {
+        const double v = (*it->lf_stats_)[s][i];
+        if (v > best_v) {
+          best_v = v;
+          best_level = i;
+        }
       }
+      enc->dqm_[s].fstrength_ = best_level;
     }
-    enc->dqm_[s].fstrength_ = best_level;
+  } else if (enc->config_->filter_strength > 0) {
+    int max_level = 0;
+    int s;
+    for (s = 0; s < NUM_MB_SEGMENTS; s++) {
+      VP8SegmentInfo* const dqm = &enc->dqm_[s];
+      // this '>> 3' accounts for some inverse WHT scaling
+      const int delta = (dqm->max_edge_ * dqm->y2_.q_[1]) >> 3;
+      const int level =
+          VP8FilterStrengthFromDelta(enc->filter_hdr_.sharpness_, delta);
+      if (level > dqm->fstrength_) {
+        dqm->fstrength_ = level;
+      }
+      if (max_level < dqm->fstrength_) {
+        max_level = dqm->fstrength_;
+      }
+    }
+    enc->filter_hdr_.level_ = max_level;
   }
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
+// -----------------------------------------------------------------------------
diff --git a/drivers/webp/enc/frame.c b/drivers/webp/enc/frame.c
index bdd360069b..5b7a40b9ad 100644
--- a/drivers/webp/enc/frame.c
+++ b/drivers/webp/enc/frame.c
@@ -1,61 +1,98 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 //   frame coding and analysis
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
-#include <assert.h>
-#include <stdlib.h>
 #include <string.h>
 #include <math.h>
 
-#include "./vp8enci.h"
 #include "./cost.h"
-
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
+#include "./vp8enci.h"
+#include "../dsp/dsp.h"
+#include "../webp/format_constants.h"  // RIFF constants
 
 #define SEGMENT_VISU 0
 #define DEBUG_SEARCH 0    // useful to track search convergence
 
-// On-the-fly info about the current set of residuals. Handy to avoid
-// passing zillions of params.
-typedef struct {
-  int first;
-  int last;
-  const int16_t* coeffs;
-
-  int coeff_type;
-  ProbaArray* prob;
-  StatsArray* stats;
-  CostArray*  cost;
-} VP8Residual;
+//------------------------------------------------------------------------------
+// multi-pass convergence
+
+#define HEADER_SIZE_ESTIMATE (RIFF_HEADER_SIZE + CHUNK_HEADER_SIZE +  \
+                              VP8_FRAME_HEADER_SIZE)
+#define DQ_LIMIT 0.4  // convergence is considered reached if dq < DQ_LIMIT
+// we allow 2k of extra head-room in PARTITION0 limit.
+#define PARTITION0_SIZE_LIMIT ((VP8_MAX_PARTITION0_SIZE - 2048ULL) << 11)
+
+typedef struct {  // struct for organizing convergence in either size or PSNR
+  int is_first;
+  float dq;
+  float q, last_q;
+  double value, last_value;   // PSNR or size
+  double target;
+  int do_size_search;
+} PassStats;
+
+static int InitPassStats(const VP8Encoder* const enc, PassStats* const s) {
+  const uint64_t target_size = (uint64_t)enc->config_->target_size;
+  const int do_size_search = (target_size != 0);
+  const float target_PSNR = enc->config_->target_PSNR;
+
+  s->is_first = 1;
+  s->dq = 10.f;
+  s->q = s->last_q = enc->config_->quality;
+  s->target = do_size_search ? (double)target_size
+            : (target_PSNR > 0.) ? target_PSNR
+            : 40.;   // default, just in case
+  s->value = s->last_value = 0.;
+  s->do_size_search = do_size_search;
+  return do_size_search;
+}
+
+static float Clamp(float v, float min, float max) {
+  return (v < min) ? min : (v > max) ? max : v;
+}
+
+static float ComputeNextQ(PassStats* const s) {
+  float dq;
+  if (s->is_first) {
+    dq = (s->value > s->target) ? -s->dq : s->dq;
+    s->is_first = 0;
+  } else if (s->value != s->last_value) {
+    const double slope = (s->target - s->value) / (s->last_value - s->value);
+    dq = (float)(slope * (s->last_q - s->q));
+  } else {
+    dq = 0.;  // we're done?!
+  }
+  // Limit variable to avoid large swings.
+  s->dq = Clamp(dq, -30.f, 30.f);
+  s->last_q = s->q;
+  s->last_value = s->value;
+  s->q = Clamp(s->q + s->dq, 0.f, 100.f);
+  return s->q;
+}
 
 //------------------------------------------------------------------------------
 // Tables for level coding
 
-const uint8_t VP8EncBands[16 + 1] = {
-  0, 1, 2, 3, 6, 4, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7,
-  0  // sentinel
-};
-
-static const uint8_t kCat3[] = { 173, 148, 140 };
-static const uint8_t kCat4[] = { 176, 155, 140, 135 };
-static const uint8_t kCat5[] = { 180, 157, 141, 134, 130 };
-static const uint8_t kCat6[] =
+const uint8_t VP8Cat3[] = { 173, 148, 140 };
+const uint8_t VP8Cat4[] = { 176, 155, 140, 135 };
+const uint8_t VP8Cat5[] = { 180, 157, 141, 134, 130 };
+const uint8_t VP8Cat6[] =
     { 254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129 };
 
 //------------------------------------------------------------------------------
 // Reset the statistics about: number of skips, token proba, level cost,...
 
 static void ResetStats(VP8Encoder* const enc) {
-  VP8Proba* const proba = &enc->proba_;
+  VP8EncProba* const proba = &enc->proba_;
   VP8CalculateLevelCosts(proba);
   proba->nb_skip_ = 0;
 }
@@ -71,7 +108,7 @@ static int CalcSkipProba(uint64_t nb, uint64_t total) {
 
 // Returns the bit-cost for coding the skip probability.
 static int FinalizeSkipProba(VP8Encoder* const enc) {
-  VP8Proba* const proba = &enc->proba_;
+  VP8EncProba* const proba = &enc->proba_;
   const int nb_mbs = enc->mb_w_ * enc->mb_h_;
   const int nb_events = proba->nb_skip_;
   int size;
@@ -86,82 +123,6 @@ static int FinalizeSkipProba(VP8Encoder* const enc) {
   return size;
 }
 
-//------------------------------------------------------------------------------
-// Recording of token probabilities.
-
-static void ResetTokenStats(VP8Encoder* const enc) {
-  VP8Proba* const proba = &enc->proba_;
-  memset(proba->stats_, 0, sizeof(proba->stats_));
-}
-
-// Record proba context used
-static int Record(int bit, proba_t* const stats) {
-  proba_t p = *stats;
-  if (p >= 0xffff0000u) {               // an overflow is inbound.
-    p = ((p + 1u) >> 1) & 0x7fff7fffu;  // -> divide the stats by 2.
-  }
-  // record bit count (lower 16 bits) and increment total count (upper 16 bits).
-  p += 0x00010000u + bit;
-  *stats = p;
-  return bit;
-}
-
-// We keep the table free variant around for reference, in case.
-#define USE_LEVEL_CODE_TABLE
-
-// Simulate block coding, but only record statistics.
-// Note: no need to record the fixed probas.
-static int RecordCoeffs(int ctx, const VP8Residual* const res) {
-  int n = res->first;
-  proba_t* s = res->stats[VP8EncBands[n]][ctx];
-  if (res->last  < 0) {
-    Record(0, s + 0);
-    return 0;
-  }
-  while (n <= res->last) {
-    int v;
-    Record(1, s + 0);
-    while ((v = res->coeffs[n++]) == 0) {
-      Record(0, s + 1);
-      s = res->stats[VP8EncBands[n]][0];
-    }
-    Record(1, s + 1);
-    if (!Record(2u < (unsigned int)(v + 1), s + 2)) {  // v = -1 or 1
-      s = res->stats[VP8EncBands[n]][1];
-    } else {
-      v = abs(v);
-#if !defined(USE_LEVEL_CODE_TABLE)
-      if (!Record(v > 4, s + 3)) {
-        if (Record(v != 2, s + 4))
-          Record(v == 4, s + 5);
-      } else if (!Record(v > 10, s + 6)) {
-        Record(v > 6, s + 7);
-      } else if (!Record((v >= 3 + (8 << 2)), s + 8)) {
-        Record((v >= 3 + (8 << 1)), s + 9);
-      } else {
-        Record((v >= 3 + (8 << 3)), s + 10);
-      }
-#else
-      if (v > MAX_VARIABLE_LEVEL)
-        v = MAX_VARIABLE_LEVEL;
-
-      {
-        const int bits = VP8LevelCodes[v - 1][1];
-        int pattern = VP8LevelCodes[v - 1][0];
-        int i;
-        for (i = 0; (pattern >>= 1) != 0; ++i) {
-          const int mask = 2 << i;
-          if (pattern & 1) Record(!!(bits & mask), s + 3 + i);
-        }
-      }
-#endif
-      s = res->stats[VP8EncBands[n]][2];
-    }
-  }
-  if (n < 16) Record(0, s + 0);
-  return 1;
-}
-
 // Collect statistics and deduce probabilities for next coding pass.
 // Return the total bit-cost for coding the probability updates.
 static int CalcTokenProba(int nb, int total) {
@@ -174,8 +135,12 @@ static int BranchCost(int nb, int total, int proba) {
   return nb * VP8BitCost(1, proba) + (total - nb) * VP8BitCost(0, proba);
 }
 
-static int FinalizeTokenProbas(VP8Encoder* const enc) {
-  VP8Proba* const proba = &enc->proba_;
+static void ResetTokenStats(VP8Encoder* const enc) {
+  VP8EncProba* const proba = &enc->proba_;
+  memset(proba->stats_, 0, sizeof(proba->stats_));
+}
+
+static int FinalizeTokenProbas(VP8EncProba* const proba) {
   int has_changed = 0;
   int size = 0;
   int t, b, c, p;
@@ -212,129 +177,44 @@ static int FinalizeTokenProbas(VP8Encoder* const enc) {
 }
 
 //------------------------------------------------------------------------------
-// helper functions for residuals struct VP8Residual.
-
-static void InitResidual(int first, int coeff_type,
-                         VP8Encoder* const enc, VP8Residual* const res) {
-  res->coeff_type = coeff_type;
-  res->prob  = enc->proba_.coeffs_[coeff_type];
-  res->stats = enc->proba_.stats_[coeff_type];
-  res->cost  = enc->proba_.level_cost_[coeff_type];
-  res->first = first;
-}
+// Finalize Segment probability based on the coding tree
 
-static void SetResidualCoeffs(const int16_t* const coeffs,
-                              VP8Residual* const res) {
-  int n;
-  res->last = -1;
-  for (n = 15; n >= res->first; --n) {
-    if (coeffs[n]) {
-      res->last = n;
-      break;
-    }
-  }
-  res->coeffs = coeffs;
+static int GetProba(int a, int b) {
+  const int total = a + b;
+  return (total == 0) ? 255     // that's the default probability.
+                      : (255 * a + total / 2) / total;  // rounded proba
 }
 
-//------------------------------------------------------------------------------
-// Mode costs
-
-static int GetResidualCost(int ctx, const VP8Residual* const res) {
-  int n = res->first;
-  int p0 = res->prob[VP8EncBands[n]][ctx][0];
-  const uint16_t* t = res->cost[VP8EncBands[n]][ctx];
-  int cost;
+static void SetSegmentProbas(VP8Encoder* const enc) {
+  int p[NUM_MB_SEGMENTS] = { 0 };
+  int n;
 
-  if (res->last < 0) {
-    return VP8BitCost(0, p0);
-  }
-  cost = 0;
-  while (n <= res->last) {
-    const int v = res->coeffs[n];
-    const int b = VP8EncBands[n + 1];
-    ++n;
-    if (v == 0) {
-      // short-case for VP8LevelCost(t, 0) (note: VP8LevelFixedCosts[0] == 0):
-      cost += t[0];
-      t = res->cost[b][0];
-      continue;
-    }
-    cost += VP8BitCost(1, p0);
-    if (2u >= (unsigned int)(v + 1)) {   // v = -1 or 1
-      // short-case for "VP8LevelCost(t, 1)" (256 is VP8LevelFixedCosts[1]):
-      cost += 256 + t[1];
-      p0 = res->prob[b][1][0];
-      t = res->cost[b][1];
-    } else {
-      cost += VP8LevelCost(t, abs(v));
-      p0 = res->prob[b][2][0];
-      t = res->cost[b][2];
-    }
+  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
+    const VP8MBInfo* const mb = &enc->mb_info_[n];
+    p[mb->segment_]++;
   }
-  if (n < 16) cost += VP8BitCost(0, p0);
-  return cost;
-}
-
-int VP8GetCostLuma4(VP8EncIterator* const it, const int16_t levels[16]) {
-  const int x = (it->i4_ & 3), y = (it->i4_ >> 2);
-  VP8Residual res;
-  VP8Encoder* const enc = it->enc_;
-  int R = 0;
-  int ctx;
-
-  InitResidual(0, 3, enc, &res);
-  ctx = it->top_nz_[x] + it->left_nz_[y];
-  SetResidualCoeffs(levels, &res);
-  R += GetResidualCost(ctx, &res);
-  return R;
-}
-
-int VP8GetCostLuma16(VP8EncIterator* const it, const VP8ModeScore* const rd) {
-  VP8Residual res;
-  VP8Encoder* const enc = it->enc_;
-  int x, y;
-  int R = 0;
-
-  VP8IteratorNzToBytes(it);   // re-import the non-zero context
-
-  // DC
-  InitResidual(0, 1, enc, &res);
-  SetResidualCoeffs(rd->y_dc_levels, &res);
-  R += GetResidualCost(it->top_nz_[8] + it->left_nz_[8], &res);
-
-  // AC
-  InitResidual(1, 0, enc, &res);
-  for (y = 0; y < 4; ++y) {
-    for (x = 0; x < 4; ++x) {
-      const int ctx = it->top_nz_[x] + it->left_nz_[y];
-      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
-      R += GetResidualCost(ctx, &res);
-      it->top_nz_[x] = it->left_nz_[y] = (res.last >= 0);
+  if (enc->pic_->stats != NULL) {
+    for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
+      enc->pic_->stats->segment_size[n] = p[n];
     }
   }
-  return R;
-}
-
-int VP8GetCostUV(VP8EncIterator* const it, const VP8ModeScore* const rd) {
-  VP8Residual res;
-  VP8Encoder* const enc = it->enc_;
-  int ch, x, y;
-  int R = 0;
-
-  VP8IteratorNzToBytes(it);  // re-import the non-zero context
-
-  InitResidual(0, 2, enc, &res);
-  for (ch = 0; ch <= 2; ch += 2) {
-    for (y = 0; y < 2; ++y) {
-      for (x = 0; x < 2; ++x) {
-        const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
-        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
-        R += GetResidualCost(ctx, &res);
-        it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] = (res.last >= 0);
-      }
-    }
+  if (enc->segment_hdr_.num_segments_ > 1) {
+    uint8_t* const probas = enc->proba_.segments_;
+    probas[0] = GetProba(p[0] + p[1], p[2] + p[3]);
+    probas[1] = GetProba(p[0], p[1]);
+    probas[2] = GetProba(p[2], p[3]);
+
+    enc->segment_hdr_.update_map_ =
+        (probas[0] != 255) || (probas[1] != 255) || (probas[2] != 255);
+    enc->segment_hdr_.size_ =
+        p[0] * (VP8BitCost(0, probas[0]) + VP8BitCost(0, probas[1])) +
+        p[1] * (VP8BitCost(0, probas[0]) + VP8BitCost(1, probas[1])) +
+        p[2] * (VP8BitCost(1, probas[0]) + VP8BitCost(0, probas[2])) +
+        p[3] * (VP8BitCost(1, probas[0]) + VP8BitCost(1, probas[2]));
+  } else {
+    enc->segment_hdr_.update_map_ = 0;
+    enc->segment_hdr_.size_ = 0;
   }
-  return R;
 }
 
 //------------------------------------------------------------------------------
@@ -342,7 +222,8 @@ int VP8GetCostUV(VP8EncIterator* const it, const VP8ModeScore* const rd) {
 
 static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
   int n = res->first;
-  const uint8_t* p = res->prob[VP8EncBands[n]][ctx];
+  // should be prob[VP8EncBands[n]], but it's equivalent for n=0 or 1
+  const uint8_t* p = res->prob[n][ctx];
   if (!VP8PutBit(bw, res->last >= 0, p[0])) {
     return 0;
   }
@@ -371,30 +252,30 @@ static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
       } else {
         int mask;
         const uint8_t* tab;
-        if (v < 3 + (8 << 1)) {          // kCat3  (3b)
+        if (v < 3 + (8 << 1)) {          // VP8Cat3  (3b)
           VP8PutBit(bw, 0, p[8]);
           VP8PutBit(bw, 0, p[9]);
           v -= 3 + (8 << 0);
           mask = 1 << 2;
-          tab = kCat3;
-        } else if (v < 3 + (8 << 2)) {   // kCat4  (4b)
+          tab = VP8Cat3;
+        } else if (v < 3 + (8 << 2)) {   // VP8Cat4  (4b)
           VP8PutBit(bw, 0, p[8]);
           VP8PutBit(bw, 1, p[9]);
           v -= 3 + (8 << 1);
           mask = 1 << 3;
-          tab = kCat4;
-        } else if (v < 3 + (8 << 3)) {   // kCat5  (5b)
+          tab = VP8Cat4;
+        } else if (v < 3 + (8 << 3)) {   // VP8Cat5  (5b)
           VP8PutBit(bw, 1, p[8]);
           VP8PutBit(bw, 0, p[10]);
           v -= 3 + (8 << 2);
           mask = 1 << 4;
-          tab = kCat5;
-        } else {                         // kCat6 (11b)
+          tab = VP8Cat5;
+        } else {                         // VP8Cat6 (11b)
           VP8PutBit(bw, 1, p[8]);
           VP8PutBit(bw, 1, p[10]);
           v -= 3 + (8 << 3);
           mask = 1 << 10;
-          tab = kCat6;
+          tab = VP8Cat6;
         }
         while (mask) {
           VP8PutBit(bw, !!(v & mask), *tab++);
@@ -411,8 +292,7 @@ static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
   return 1;
 }
 
-static void CodeResiduals(VP8BitWriter* const bw,
-                          VP8EncIterator* const it,
+static void CodeResiduals(VP8BitWriter* const bw, VP8EncIterator* const it,
                           const VP8ModeScore* const rd) {
   int x, y, ch;
   VP8Residual res;
@@ -425,32 +305,32 @@ static void CodeResiduals(VP8BitWriter* const bw,
 
   pos1 = VP8BitWriterPos(bw);
   if (i16) {
-    InitResidual(0, 1, enc, &res);
-    SetResidualCoeffs(rd->y_dc_levels, &res);
+    VP8InitResidual(0, 1, enc, &res);
+    VP8SetResidualCoeffs(rd->y_dc_levels, &res);
     it->top_nz_[8] = it->left_nz_[8] =
       PutCoeffs(bw, it->top_nz_[8] + it->left_nz_[8], &res);
-    InitResidual(1, 0, enc, &res);
+    VP8InitResidual(1, 0, enc, &res);
   } else {
-    InitResidual(0, 3, enc, &res);
+    VP8InitResidual(0, 3, enc, &res);
   }
 
   // luma-AC
   for (y = 0; y < 4; ++y) {
     for (x = 0; x < 4; ++x) {
       const int ctx = it->top_nz_[x] + it->left_nz_[y];
-      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
+      VP8SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
       it->top_nz_[x] = it->left_nz_[y] = PutCoeffs(bw, ctx, &res);
     }
   }
   pos2 = VP8BitWriterPos(bw);
 
   // U/V
-  InitResidual(0, 2, enc, &res);
+  VP8InitResidual(0, 2, enc, &res);
   for (ch = 0; ch <= 2; ch += 2) {
     for (y = 0; y < 2; ++y) {
       for (x = 0; x < 2; ++x) {
         const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
-        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
+        VP8SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
         it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
             PutCoeffs(bw, ctx, &res);
       }
@@ -475,33 +355,33 @@ static void RecordResiduals(VP8EncIterator* const it,
   VP8IteratorNzToBytes(it);
 
   if (it->mb_->type_ == 1) {   // i16x16
-    InitResidual(0, 1, enc, &res);
-    SetResidualCoeffs(rd->y_dc_levels, &res);
+    VP8InitResidual(0, 1, enc, &res);
+    VP8SetResidualCoeffs(rd->y_dc_levels, &res);
     it->top_nz_[8] = it->left_nz_[8] =
-      RecordCoeffs(it->top_nz_[8] + it->left_nz_[8], &res);
-    InitResidual(1, 0, enc, &res);
+      VP8RecordCoeffs(it->top_nz_[8] + it->left_nz_[8], &res);
+    VP8InitResidual(1, 0, enc, &res);
   } else {
-    InitResidual(0, 3, enc, &res);
+    VP8InitResidual(0, 3, enc, &res);
   }
 
   // luma-AC
   for (y = 0; y < 4; ++y) {
     for (x = 0; x < 4; ++x) {
       const int ctx = it->top_nz_[x] + it->left_nz_[y];
-      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
-      it->top_nz_[x] = it->left_nz_[y] = RecordCoeffs(ctx, &res);
+      VP8SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
+      it->top_nz_[x] = it->left_nz_[y] = VP8RecordCoeffs(ctx, &res);
     }
   }
 
   // U/V
-  InitResidual(0, 2, enc, &res);
+  VP8InitResidual(0, 2, enc, &res);
   for (ch = 0; ch <= 2; ch += 2) {
     for (y = 0; y < 2; ++y) {
       for (x = 0; x < 2; ++x) {
         const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
-        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
+        VP8SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
         it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
-            RecordCoeffs(ctx, &res);
+            VP8RecordCoeffs(ctx, &res);
       }
     }
   }
@@ -512,176 +392,59 @@ static void RecordResiduals(VP8EncIterator* const it,
 //------------------------------------------------------------------------------
 // Token buffer
 
-#ifdef USE_TOKEN_BUFFER
-
-void VP8TBufferInit(VP8TBuffer* const b) {
-  b->rows_ = NULL;
-  b->tokens_ = NULL;
-  b->last_ = &b->rows_;
-  b->left_ = 0;
-  b->error_ = 0;
-}
-
-int VP8TBufferNewPage(VP8TBuffer* const b) {
-  VP8Tokens* const page = b->error_ ? NULL : (VP8Tokens*)malloc(sizeof(*page));
-  if (page == NULL) {
-    b->error_ = 1;
-    return 0;
-  }
-  *b->last_ = page;
-  b->last_ = &page->next_;
-  b->left_ = MAX_NUM_TOKEN;
-  b->tokens_ = page->tokens_;
-  return 1;
-}
-
-void VP8TBufferClear(VP8TBuffer* const b) {
-  if (b != NULL) {
-    const VP8Tokens* p = b->rows_;
-    while (p != NULL) {
-      const VP8Tokens* const next = p->next_;
-      free((void*)p);
-      p = next;
-    }
-    VP8TBufferInit(b);
-  }
-}
-
-int VP8EmitTokens(const VP8TBuffer* const b, VP8BitWriter* const bw,
-                  const uint8_t* const probas) {
-  VP8Tokens* p = b->rows_;
-  if (b->error_) return 0;
-  while (p != NULL) {
-    const int N = (p->next_ == NULL) ? b->left_ : 0;
-    int n = MAX_NUM_TOKEN;
-    while (n-- > N) {
-      VP8PutBit(bw, (p->tokens_[n] >> 15) & 1, probas[p->tokens_[n] & 0x7fff]);
-    }
-    p = p->next_;
-  }
-  return 1;
-}
-
-#define TOKEN_ID(b, ctx, p) ((p) + NUM_PROBAS * ((ctx) + (b) * NUM_CTX))
-
-static int RecordCoeffTokens(int ctx, const VP8Residual* const res,
-                             VP8TBuffer* tokens) {
-  int n = res->first;
-  int b = VP8EncBands[n];
-  if (!VP8AddToken(tokens, res->last >= 0, TOKEN_ID(b, ctx, 0))) {
-    return 0;
-  }
-
-  while (n < 16) {
-    const int c = res->coeffs[n++];
-    const int sign = c < 0;
-    int v = sign ? -c : c;
-    const int base_id = TOKEN_ID(b, ctx, 0);
-    if (!VP8AddToken(tokens, v != 0, base_id + 1)) {
-      b = VP8EncBands[n];
-      ctx = 0;
-      continue;
-    }
-    if (!VP8AddToken(tokens, v > 1, base_id + 2)) {
-      b = VP8EncBands[n];
-      ctx = 1;
-    } else {
-      if (!VP8AddToken(tokens, v > 4, base_id + 3)) {
-        if (VP8AddToken(tokens, v != 2, base_id + 4))
-          VP8AddToken(tokens, v == 4, base_id + 5);
-      } else if (!VP8AddToken(tokens, v > 10, base_id + 6)) {
-        if (!VP8AddToken(tokens, v > 6, base_id + 7)) {
-//          VP8AddToken(tokens, v == 6, 159);
-        } else {
-//          VP8AddToken(tokens, v >= 9, 165);
-//          VP8AddToken(tokens, !(v & 1), 145);
-        }
-      } else {
-        int mask;
-        const uint8_t* tab;
-        if (v < 3 + (8 << 1)) {          // kCat3  (3b)
-          VP8AddToken(tokens, 0, base_id + 8);
-          VP8AddToken(tokens, 0, base_id + 9);
-          v -= 3 + (8 << 0);
-          mask = 1 << 2;
-          tab = kCat3;
-        } else if (v < 3 + (8 << 2)) {   // kCat4  (4b)
-          VP8AddToken(tokens, 0, base_id + 8);
-          VP8AddToken(tokens, 1, base_id + 9);
-          v -= 3 + (8 << 1);
-          mask = 1 << 3;
-          tab = kCat4;
-        } else if (v < 3 + (8 << 3)) {   // kCat5  (5b)
-          VP8AddToken(tokens, 1, base_id + 8);
-          VP8AddToken(tokens, 0, base_id + 10);
-          v -= 3 + (8 << 2);
-          mask = 1 << 4;
-          tab = kCat5;
-        } else {                         // kCat6 (11b)
-          VP8AddToken(tokens, 1, base_id + 8);
-          VP8AddToken(tokens, 1, base_id + 10);
-          v -= 3 + (8 << 3);
-          mask = 1 << 10;
-          tab = kCat6;
-        }
-        while (mask) {
-          // VP8AddToken(tokens, !!(v & mask), *tab++);
-          mask >>= 1;
-        }
-      }
-      ctx = 2;
-    }
-    b = VP8EncBands[n];
-    // VP8PutBitUniform(bw, sign);
-    if (n == 16 || !VP8AddToken(tokens, n <= res->last, TOKEN_ID(b, ctx, 0))) {
-      return 1;   // EOB
-    }
-  }
-  return 1;
-}
+#if !defined(DISABLE_TOKEN_BUFFER)
 
-static void RecordTokens(VP8EncIterator* const it,
-                         const VP8ModeScore* const rd, VP8TBuffer tokens[2]) {
+static int RecordTokens(VP8EncIterator* const it, const VP8ModeScore* const rd,
+                        VP8TBuffer* const tokens) {
   int x, y, ch;
   VP8Residual res;
   VP8Encoder* const enc = it->enc_;
 
   VP8IteratorNzToBytes(it);
   if (it->mb_->type_ == 1) {   // i16x16
-    InitResidual(0, 1, enc, &res);
-    SetResidualCoeffs(rd->y_dc_levels, &res);
-// TODO(skal): FIX ->    it->top_nz_[8] = it->left_nz_[8] =
-      RecordCoeffTokens(it->top_nz_[8] + it->left_nz_[8], &res, &tokens[0]);
-    InitResidual(1, 0, enc, &res);
+    const int ctx = it->top_nz_[8] + it->left_nz_[8];
+    VP8InitResidual(0, 1, enc, &res);
+    VP8SetResidualCoeffs(rd->y_dc_levels, &res);
+    it->top_nz_[8] = it->left_nz_[8] =
+        VP8RecordCoeffTokens(ctx, 1,
+                             res.first, res.last, res.coeffs, tokens);
+    VP8RecordCoeffs(ctx, &res);
+    VP8InitResidual(1, 0, enc, &res);
   } else {
-    InitResidual(0, 3, enc, &res);
+    VP8InitResidual(0, 3, enc, &res);
   }
 
   // luma-AC
   for (y = 0; y < 4; ++y) {
     for (x = 0; x < 4; ++x) {
       const int ctx = it->top_nz_[x] + it->left_nz_[y];
-      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
+      VP8SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
       it->top_nz_[x] = it->left_nz_[y] =
-          RecordCoeffTokens(ctx, &res, &tokens[0]);
+          VP8RecordCoeffTokens(ctx, res.coeff_type,
+                               res.first, res.last, res.coeffs, tokens);
+      VP8RecordCoeffs(ctx, &res);
     }
   }
 
   // U/V
-  InitResidual(0, 2, enc, &res);
+  VP8InitResidual(0, 2, enc, &res);
   for (ch = 0; ch <= 2; ch += 2) {
     for (y = 0; y < 2; ++y) {
       for (x = 0; x < 2; ++x) {
         const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
-        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
+        VP8SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
         it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
-            RecordCoeffTokens(ctx, &res, &tokens[1]);
+            VP8RecordCoeffTokens(ctx, 2,
+                                 res.first, res.last, res.coeffs, tokens);
+        VP8RecordCoeffs(ctx, &res);
       }
     }
   }
+  VP8IteratorBytesToNz(it);
+  return !tokens->error_;
 }
 
-#endif    // USE_TOKEN_BUFFER
+#endif    // !DISABLE_TOKEN_BUFFER
 
 //------------------------------------------------------------------------------
 // ExtraInfo map / Debug function
@@ -697,7 +460,10 @@ static void SetBlock(uint8_t* p, int value, int size) {
 #endif
 
 static void ResetSSE(VP8Encoder* const enc) {
-  memset(enc->sse_, 0, sizeof(enc->sse_));
+  enc->sse_[0] = 0;
+  enc->sse_[1] = 0;
+  enc->sse_[2] = 0;
+  // Note: enc->sse_[3] is managed by alpha.c
   enc->sse_count_ = 0;
 }
 
@@ -706,9 +472,9 @@ static void StoreSSE(const VP8EncIterator* const it) {
   const uint8_t* const in = it->yuv_in_;
   const uint8_t* const out = it->yuv_out_;
   // Note: not totally accurate at boundary. And doesn't include in-loop filter.
-  enc->sse_[0] += VP8SSE16x16(in + Y_OFF, out + Y_OFF);
-  enc->sse_[1] += VP8SSE8x8(in + U_OFF, out + U_OFF);
-  enc->sse_[2] += VP8SSE8x8(in + V_OFF, out + V_OFF);
+  enc->sse_[0] += VP8SSE16x16(in + Y_OFF_ENC, out + Y_OFF_ENC);
+  enc->sse_[1] += VP8SSE8x8(in + U_OFF_ENC, out + U_OFF_ENC);
+  enc->sse_[2] += VP8SSE8x8(in + V_OFF_ENC, out + V_OFF_ENC);
   enc->sse_count_ += 16 * 16;
 }
 
@@ -736,72 +502,163 @@ static void StoreSideInfo(const VP8EncIterator* const it) {
         const int b = (int)((it->luma_bits_ + it->uv_bits_ + 7) >> 3);
         *info = (b > 255) ? 255 : b; break;
       }
+      case 7: *info = mb->alpha_; break;
       default: *info = 0; break;
-    };
+    }
   }
 #if SEGMENT_VISU  // visualize segments and prediction modes
-  SetBlock(it->yuv_out_ + Y_OFF, mb->segment_ * 64, 16);
-  SetBlock(it->yuv_out_ + U_OFF, it->preds_[0] * 64, 8);
-  SetBlock(it->yuv_out_ + V_OFF, mb->uv_mode_ * 64, 8);
+  SetBlock(it->yuv_out_ + Y_OFF_ENC, mb->segment_ * 64, 16);
+  SetBlock(it->yuv_out_ + U_OFF_ENC, it->preds_[0] * 64, 8);
+  SetBlock(it->yuv_out_ + V_OFF_ENC, mb->uv_mode_ * 64, 8);
 #endif
 }
 
-//------------------------------------------------------------------------------
-// Main loops
-//
-//  VP8EncLoop(): does the final bitstream coding.
-
-static void ResetAfterSkip(VP8EncIterator* const it) {
-  if (it->mb_->type_ == 1) {
-    *it->nz_ = 0;  // reset all predictors
-    it->left_nz_[8] = 0;
-  } else {
-    *it->nz_ &= (1 << 24);  // preserve the dc_nz bit
-  }
+static double GetPSNR(uint64_t mse, uint64_t size) {
+  return (mse > 0 && size > 0) ? 10. * log10(255. * 255. * size / mse) : 99;
 }
 
-int VP8EncLoop(VP8Encoder* const enc) {
-  int i, s, p;
-  int ok = 1;
-  VP8EncIterator it;
-  VP8ModeScore info;
-  const int dont_use_skip = !enc->proba_.use_skip_proba_;
-  const int rd_opt = enc->rd_opt_level_;
-  const int kAverageBytesPerMB = 5;     // TODO: have a kTable[quality/10]
-  const int bytes_per_parts =
-    enc->mb_w_ * enc->mb_h_ * kAverageBytesPerMB / enc->num_parts_;
+//------------------------------------------------------------------------------
+//  StatLoop(): only collect statistics (number of skips, token usage, ...).
+//  This is used for deciding optimal probabilities. It also modifies the
+//  quantizer value if some target (size, PSNR) was specified.
 
-  // Initialize the bit-writers
-  for (p = 0; p < enc->num_parts_; ++p) {
-    VP8BitWriterInit(enc->parts_ + p, bytes_per_parts);
-  }
+static void SetLoopParams(VP8Encoder* const enc, float q) {
+  // Make sure the quality parameter is inside valid bounds
+  q = Clamp(q, 0.f, 100.f);
+
+  VP8SetSegmentParams(enc, q);      // setup segment quantizations and filters
+  SetSegmentProbas(enc);            // compute segment probabilities
 
   ResetStats(enc);
   ResetSSE(enc);
+}
+
+static uint64_t OneStatPass(VP8Encoder* const enc, VP8RDLevel rd_opt,
+                            int nb_mbs, int percent_delta,
+                            PassStats* const s) {
+  VP8EncIterator it;
+  uint64_t size = 0;
+  uint64_t size_p0 = 0;
+  uint64_t distortion = 0;
+  const uint64_t pixel_count = nb_mbs * 384;
 
   VP8IteratorInit(enc, &it);
-  VP8InitFilter(&it);
+  SetLoopParams(enc, s->q);
   do {
-    VP8IteratorImport(&it);
-    // Warning! order is important: first call VP8Decimate() and
-    // *then* decide how to code the skip decision if there's one.
-    if (!VP8Decimate(&it, &info, rd_opt) || dont_use_skip) {
-      CodeResiduals(it.bw_, &it, &info);
-    } else {   // reset predictors after a skip
-      ResetAfterSkip(&it);
+    VP8ModeScore info;
+    VP8IteratorImport(&it, NULL);
+    if (VP8Decimate(&it, &info, rd_opt)) {
+      // Just record the number of skips and act like skip_proba is not used.
+      enc->proba_.nb_skip_++;
     }
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    if (enc->use_layer_) {
-      VP8EncCodeLayerBlock(&it);
+    RecordResiduals(&it, &info);
+    size += info.R + info.H;
+    size_p0 += info.H;
+    distortion += info.D;
+    if (percent_delta && !VP8IteratorProgress(&it, percent_delta))
+      return 0;
+    VP8IteratorSaveBoundary(&it);
+  } while (VP8IteratorNext(&it) && --nb_mbs > 0);
+
+  size_p0 += enc->segment_hdr_.size_;
+  if (s->do_size_search) {
+    size += FinalizeSkipProba(enc);
+    size += FinalizeTokenProbas(&enc->proba_);
+    size = ((size + size_p0 + 1024) >> 11) + HEADER_SIZE_ESTIMATE;
+    s->value = (double)size;
+  } else {
+    s->value = GetPSNR(distortion, pixel_count);
+  }
+  return size_p0;
+}
+
+static int StatLoop(VP8Encoder* const enc) {
+  const int method = enc->method_;
+  const int do_search = enc->do_search_;
+  const int fast_probe = ((method == 0 || method == 3) && !do_search);
+  int num_pass_left = enc->config_->pass;
+  const int task_percent = 20;
+  const int percent_per_pass =
+      (task_percent + num_pass_left / 2) / num_pass_left;
+  const int final_percent = enc->percent_ + task_percent;
+  const VP8RDLevel rd_opt =
+      (method >= 3 || do_search) ? RD_OPT_BASIC : RD_OPT_NONE;
+  int nb_mbs = enc->mb_w_ * enc->mb_h_;
+  PassStats stats;
+
+  InitPassStats(enc, &stats);
+  ResetTokenStats(enc);
+
+  // Fast mode: quick analysis pass over few mbs. Better than nothing.
+  if (fast_probe) {
+    if (method == 3) {  // we need more stats for method 3 to be reliable.
+      nb_mbs = (nb_mbs > 200) ? nb_mbs >> 1 : 100;
+    } else {
+      nb_mbs = (nb_mbs > 200) ? nb_mbs >> 2 : 50;
     }
+  }
+
+  while (num_pass_left-- > 0) {
+    const int is_last_pass = (fabs(stats.dq) <= DQ_LIMIT) ||
+                             (num_pass_left == 0) ||
+                             (enc->max_i4_header_bits_ == 0);
+    const uint64_t size_p0 =
+        OneStatPass(enc, rd_opt, nb_mbs, percent_per_pass, &stats);
+    if (size_p0 == 0) return 0;
+#if (DEBUG_SEARCH > 0)
+    printf("#%d value:%.1lf -> %.1lf   q:%.2f -> %.2f\n",
+           num_pass_left, stats.last_value, stats.value, stats.last_q, stats.q);
 #endif
-    StoreSideInfo(&it);
-    VP8StoreFilterStats(&it);
-    VP8IteratorExport(&it);
-    ok = VP8IteratorProgress(&it, 20);
-  } while (ok && VP8IteratorNext(&it, it.yuv_out_));
+    if (enc->max_i4_header_bits_ > 0 && size_p0 > PARTITION0_SIZE_LIMIT) {
+      ++num_pass_left;
+      enc->max_i4_header_bits_ >>= 1;  // strengthen header bit limitation...
+      continue;                        // ...and start over
+    }
+    if (is_last_pass) {
+      break;
+    }
+    // If no target size: just do several pass without changing 'q'
+    if (do_search) {
+      ComputeNextQ(&stats);
+      if (fabs(stats.dq) <= DQ_LIMIT) break;
+    }
+  }
+  if (!do_search || !stats.do_size_search) {
+    // Need to finalize probas now, since it wasn't done during the search.
+    FinalizeSkipProba(enc);
+    FinalizeTokenProbas(&enc->proba_);
+  }
+  VP8CalculateLevelCosts(&enc->proba_);  // finalize costs
+  return WebPReportProgress(enc->pic_, final_percent, &enc->percent_);
+}
+
+//------------------------------------------------------------------------------
+// Main loops
+//
+
+static const int kAverageBytesPerMB[8] = { 50, 24, 16, 9, 7, 5, 3, 2 };
 
+static int PreLoopInitialize(VP8Encoder* const enc) {
+  int p;
+  int ok = 1;
+  const int average_bytes_per_MB = kAverageBytesPerMB[enc->base_quant_ >> 4];
+  const int bytes_per_parts =
+      enc->mb_w_ * enc->mb_h_ * average_bytes_per_MB / enc->num_parts_;
+  // Initialize the bit-writers
+  for (p = 0; ok && p < enc->num_parts_; ++p) {
+    ok = VP8BitWriterInit(enc->parts_ + p, bytes_per_parts);
+  }
+  if (!ok) {
+    VP8EncFreeBitWriters(enc);  // malloc error occurred
+    WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
+  }
+  return ok;
+}
+
+static int PostLoopFinalize(VP8EncIterator* const it, int ok) {
+  VP8Encoder* const enc = it->enc_;
   if (ok) {      // Finalize the partitions, check for extra errors.
+    int p;
     for (p = 0; p < enc->num_parts_; ++p) {
       VP8BitWriterFinish(enc->parts_ + p);
       ok &= !enc->parts_[p].error_;
@@ -809,131 +666,185 @@ int VP8EncLoop(VP8Encoder* const enc) {
   }
 
   if (ok) {      // All good. Finish up.
-    if (enc->pic_->stats) {           // finalize byte counters...
+    if (enc->pic_->stats != NULL) {  // finalize byte counters...
+      int i, s;
       for (i = 0; i <= 2; ++i) {
         for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
-          enc->residual_bytes_[i][s] = (int)((it.bit_count_[s][i] + 7) >> 3);
+          enc->residual_bytes_[i][s] = (int)((it->bit_count_[s][i] + 7) >> 3);
         }
       }
     }
-    VP8AdjustFilterStrength(&it);     // ...and store filter stats.
+    VP8AdjustFilterStrength(it);     // ...and store filter stats.
   } else {
     // Something bad happened -> need to do some memory cleanup.
     VP8EncFreeBitWriters(enc);
   }
-
   return ok;
 }
 
 //------------------------------------------------------------------------------
-//  VP8StatLoop(): only collect statistics (number of skips, token usage, ...)
-//                 This is used for deciding optimal probabilities. It also
-//                 modifies the quantizer value if some target (size, PNSR)
-//                 was specified.
-
-#define kHeaderSizeEstimate (15 + 20 + 10)      // TODO: fix better
-
-static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
-                       float* const PSNR, int percent_delta) {
-  VP8EncIterator it;
-  uint64_t size = 0;
-  uint64_t distortion = 0;
-  const uint64_t pixel_count = nb_mbs * 384;
+//  VP8EncLoop(): does the final bitstream coding.
 
-  // Make sure the quality parameter is inside valid bounds
-  if (q < 0.) {
-    q = 0;
-  } else if (q > 100.) {
-    q = 100;
+static void ResetAfterSkip(VP8EncIterator* const it) {
+  if (it->mb_->type_ == 1) {
+    *it->nz_ = 0;  // reset all predictors
+    it->left_nz_[8] = 0;
+  } else {
+    *it->nz_ &= (1 << 24);  // preserve the dc_nz bit
   }
+}
 
-  VP8SetSegmentParams(enc, q);      // setup segment quantizations and filters
+int VP8EncLoop(VP8Encoder* const enc) {
+  VP8EncIterator it;
+  int ok = PreLoopInitialize(enc);
+  if (!ok) return 0;
 
-  ResetStats(enc);
-  ResetTokenStats(enc);
+  StatLoop(enc);  // stats-collection loop
 
   VP8IteratorInit(enc, &it);
+  VP8InitFilter(&it);
   do {
     VP8ModeScore info;
-    VP8IteratorImport(&it);
-    if (VP8Decimate(&it, &info, rd_opt)) {
-      // Just record the number of skips and act like skip_proba is not used.
-      enc->proba_.nb_skip_++;
+    const int dont_use_skip = !enc->proba_.use_skip_proba_;
+    const VP8RDLevel rd_opt = enc->rd_opt_level_;
+
+    VP8IteratorImport(&it, NULL);
+    // Warning! order is important: first call VP8Decimate() and
+    // *then* decide how to code the skip decision if there's one.
+    if (!VP8Decimate(&it, &info, rd_opt) || dont_use_skip) {
+      CodeResiduals(it.bw_, &it, &info);
+    } else {   // reset predictors after a skip
+      ResetAfterSkip(&it);
     }
-    RecordResiduals(&it, &info);
-    size += info.R;
-    distortion += info.D;
-    if (percent_delta && !VP8IteratorProgress(&it, percent_delta))
-      return 0;
-  } while (VP8IteratorNext(&it, it.yuv_out_) && --nb_mbs > 0);
-  size += FinalizeSkipProba(enc);
-  size += FinalizeTokenProbas(enc);
-  size += enc->segment_hdr_.size_;
-  size = ((size + 1024) >> 11) + kHeaderSizeEstimate;
-
-  if (PSNR) {
-    *PSNR = (float)(10.* log10(255. * 255. * pixel_count / distortion));
-  }
-  return (int)size;
+    StoreSideInfo(&it);
+    VP8StoreFilterStats(&it);
+    VP8IteratorExport(&it);
+    ok = VP8IteratorProgress(&it, 20);
+    VP8IteratorSaveBoundary(&it);
+  } while (ok && VP8IteratorNext(&it));
+
+  return PostLoopFinalize(&it, ok);
 }
 
-// successive refinement increments.
-static const int dqs[] = { 20, 15, 10, 8, 6, 4, 2, 1, 0 };
+//------------------------------------------------------------------------------
+// Single pass using Token Buffer.
 
-int VP8StatLoop(VP8Encoder* const enc) {
-  const int do_search =
-    (enc->config_->target_size > 0 || enc->config_->target_PSNR > 0);
-  const int fast_probe = (enc->method_ < 2 && !do_search);
-  float q = enc->config_->quality;
-  const int max_passes = enc->config_->pass;
-  const int task_percent = 20;
-  const int percent_per_pass = (task_percent + max_passes / 2) / max_passes;
-  const int final_percent = enc->percent_ + task_percent;
-  int pass;
-  int nb_mbs;
+#if !defined(DISABLE_TOKEN_BUFFER)
 
-  // Fast mode: quick analysis pass over few mbs. Better than nothing.
-  nb_mbs = enc->mb_w_ * enc->mb_h_;
-  if (fast_probe && nb_mbs > 100) nb_mbs = 100;
-
-  // No target size: just do several pass without changing 'q'
-  if (!do_search) {
-    for (pass = 0; pass < max_passes; ++pass) {
-      const int rd_opt = (enc->method_ > 2);
-      if (!OneStatPass(enc, q, rd_opt, nb_mbs, NULL, percent_per_pass)) {
-        return 0;
-      }
+#define MIN_COUNT 96  // minimum number of macroblocks before updating stats
+
+int VP8EncTokenLoop(VP8Encoder* const enc) {
+  // Roughly refresh the proba eight times per pass
+  int max_count = (enc->mb_w_ * enc->mb_h_) >> 3;
+  int num_pass_left = enc->config_->pass;
+  const int do_search = enc->do_search_;
+  VP8EncIterator it;
+  VP8EncProba* const proba = &enc->proba_;
+  const VP8RDLevel rd_opt = enc->rd_opt_level_;
+  const uint64_t pixel_count = enc->mb_w_ * enc->mb_h_ * 384;
+  PassStats stats;
+  int ok;
+
+  InitPassStats(enc, &stats);
+  ok = PreLoopInitialize(enc);
+  if (!ok) return 0;
+
+  if (max_count < MIN_COUNT) max_count = MIN_COUNT;
+
+  assert(enc->num_parts_ == 1);
+  assert(enc->use_tokens_);
+  assert(proba->use_skip_proba_ == 0);
+  assert(rd_opt >= RD_OPT_BASIC);   // otherwise, token-buffer won't be useful
+  assert(num_pass_left > 0);
+
+  while (ok && num_pass_left-- > 0) {
+    const int is_last_pass = (fabs(stats.dq) <= DQ_LIMIT) ||
+                             (num_pass_left == 0) ||
+                             (enc->max_i4_header_bits_ == 0);
+    uint64_t size_p0 = 0;
+    uint64_t distortion = 0;
+    int cnt = max_count;
+    VP8IteratorInit(enc, &it);
+    SetLoopParams(enc, stats.q);
+    if (is_last_pass) {
+      ResetTokenStats(enc);
+      VP8InitFilter(&it);  // don't collect stats until last pass (too costly)
     }
-  } else {
-    // binary search for a size close to target
-    for (pass = 0; pass < max_passes && (dqs[pass] > 0); ++pass) {
-      const int rd_opt = 1;
-      float PSNR;
-      int criterion;
-      const int size = OneStatPass(enc, q, rd_opt, nb_mbs, &PSNR,
-                                   percent_per_pass);
-#if DEBUG_SEARCH
-      printf("#%d size=%d PSNR=%.2f q=%.2f\n", pass, size, PSNR, q);
-#endif
-      if (!size) return 0;
-      if (enc->config_->target_PSNR > 0) {
-        criterion = (PSNR < enc->config_->target_PSNR);
-      } else {
-        criterion = (size < enc->config_->target_size);
+    VP8TBufferClear(&enc->tokens_);
+    do {
+      VP8ModeScore info;
+      VP8IteratorImport(&it, NULL);
+      if (--cnt < 0) {
+        FinalizeTokenProbas(proba);
+        VP8CalculateLevelCosts(proba);  // refresh cost tables for rd-opt
+        cnt = max_count;
       }
-      // dichotomize
-      if (criterion) {
-        q += dqs[pass];
-      } else {
-        q -= dqs[pass];
+      VP8Decimate(&it, &info, rd_opt);
+      ok = RecordTokens(&it, &info, &enc->tokens_);
+      if (!ok) {
+        WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
+        break;
+      }
+      size_p0 += info.H;
+      distortion += info.D;
+      if (is_last_pass) {
+        StoreSideInfo(&it);
+        VP8StoreFilterStats(&it);
+        VP8IteratorExport(&it);
+        ok = VP8IteratorProgress(&it, 20);
       }
+      VP8IteratorSaveBoundary(&it);
+    } while (ok && VP8IteratorNext(&it));
+    if (!ok) break;
+
+    size_p0 += enc->segment_hdr_.size_;
+    if (stats.do_size_search) {
+      uint64_t size = FinalizeTokenProbas(&enc->proba_);
+      size += VP8EstimateTokenSize(&enc->tokens_,
+                                   (const uint8_t*)proba->coeffs_);
+      size = (size + size_p0 + 1024) >> 11;  // -> size in bytes
+      size += HEADER_SIZE_ESTIMATE;
+      stats.value = (double)size;
+    } else {  // compute and store PSNR
+      stats.value = GetPSNR(distortion, pixel_count);
+    }
+
+#if (DEBUG_SEARCH > 0)
+    printf("#%2d metric:%.1lf -> %.1lf   last_q=%.2lf q=%.2lf dq=%.2lf\n",
+           num_pass_left, stats.last_value, stats.value,
+           stats.last_q, stats.q, stats.dq);
+#endif
+    if (size_p0 > PARTITION0_SIZE_LIMIT) {
+      ++num_pass_left;
+      enc->max_i4_header_bits_ >>= 1;  // strengthen header bit limitation...
+      continue;                        // ...and start over
+    }
+    if (is_last_pass) {
+      break;   // done
+    }
+    if (do_search) {
+      ComputeNextQ(&stats);  // Adjust q
     }
   }
-  return WebPReportProgress(enc->pic_, final_percent, &enc->percent_);
+  if (ok) {
+    if (!stats.do_size_search) {
+      FinalizeTokenProbas(&enc->proba_);
+    }
+    ok = VP8EmitTokens(&enc->tokens_, enc->parts_ + 0,
+                       (const uint8_t*)proba->coeffs_, 1);
+  }
+  ok = ok && WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
+  return PostLoopFinalize(&it, ok);
+}
+
+#else
+
+int VP8EncTokenLoop(VP8Encoder* const enc) {
+  (void)enc;
+  return 0;   // we shouldn't be here.
 }
 
+#endif    // DISABLE_TOKEN_BUFFER
+
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/histogram.c b/drivers/webp/enc/histogram.c
index ca838e064d..62c320d809 100644
--- a/drivers/webp/enc/histogram.c
+++ b/drivers/webp/enc/histogram.c
@@ -1,38 +1,82 @@
 // Copyright 2012 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Author: Jyrki Alakuijala (jyrki@google.com)
 //
 #ifdef HAVE_CONFIG_H
-#include "config.h"
+#include "../webp/config.h"
 #endif
 
 #include <math.h>
-#include <stdio.h>
 
 #include "./backward_references.h"
 #include "./histogram.h"
 #include "../dsp/lossless.h"
 #include "../utils/utils.h"
 
+#define MAX_COST 1.e38
+
+// Number of partitions for the three dominant (literal, red and blue) symbol
+// costs.
+#define NUM_PARTITIONS 4
+// The size of the bin-hash corresponding to the three dominant costs.
+#define BIN_SIZE (NUM_PARTITIONS * NUM_PARTITIONS * NUM_PARTITIONS)
+// Maximum number of histograms allowed in greedy combining algorithm.
+#define MAX_HISTO_GREEDY 100
+
 static void HistogramClear(VP8LHistogram* const p) {
-  memset(p->literal_, 0, sizeof(p->literal_));
-  memset(p->red_, 0, sizeof(p->red_));
-  memset(p->blue_, 0, sizeof(p->blue_));
-  memset(p->alpha_, 0, sizeof(p->alpha_));
-  memset(p->distance_, 0, sizeof(p->distance_));
-  p->bit_cost_ = 0;
+  uint32_t* const literal = p->literal_;
+  const int cache_bits = p->palette_code_bits_;
+  const int histo_size = VP8LGetHistogramSize(cache_bits);
+  memset(p, 0, histo_size);
+  p->palette_code_bits_ = cache_bits;
+  p->literal_ = literal;
+}
+
+// Swap two histogram pointers.
+static void HistogramSwap(VP8LHistogram** const A, VP8LHistogram** const B) {
+  VP8LHistogram* const tmp = *A;
+  *A = *B;
+  *B = tmp;
+}
+
+static void HistogramCopy(const VP8LHistogram* const src,
+                          VP8LHistogram* const dst) {
+  uint32_t* const dst_literal = dst->literal_;
+  const int dst_cache_bits = dst->palette_code_bits_;
+  const int histo_size = VP8LGetHistogramSize(dst_cache_bits);
+  assert(src->palette_code_bits_ == dst_cache_bits);
+  memcpy(dst, src, histo_size);
+  dst->literal_ = dst_literal;
+}
+
+int VP8LGetHistogramSize(int cache_bits) {
+  const int literal_size = VP8LHistogramNumCodes(cache_bits);
+  const size_t total_size = sizeof(VP8LHistogram) + sizeof(int) * literal_size;
+  assert(total_size <= (size_t)0x7fffffff);
+  return (int)total_size;
+}
+
+void VP8LFreeHistogram(VP8LHistogram* const histo) {
+  WebPSafeFree(histo);
+}
+
+void VP8LFreeHistogramSet(VP8LHistogramSet* const histo) {
+  WebPSafeFree(histo);
 }
 
 void VP8LHistogramStoreRefs(const VP8LBackwardRefs* const refs,
                             VP8LHistogram* const histo) {
-  int i;
-  for (i = 0; i < refs->size; ++i) {
-    VP8LHistogramAddSinglePixOrCopy(histo, &refs->refs[i]);
+  VP8LRefsCursor c = VP8LRefsCursorInit(refs);
+  while (VP8LRefsCursorOk(&c)) {
+    VP8LHistogramAddSinglePixOrCopy(histo, c.cur_pos);
+    VP8LRefsCursorNext(&c);
   }
 }
 
@@ -51,13 +95,25 @@ void VP8LHistogramInit(VP8LHistogram* const p, int palette_code_bits) {
   HistogramClear(p);
 }
 
+VP8LHistogram* VP8LAllocateHistogram(int cache_bits) {
+  VP8LHistogram* histo = NULL;
+  const int total_size = VP8LGetHistogramSize(cache_bits);
+  uint8_t* const memory = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*memory));
+  if (memory == NULL) return NULL;
+  histo = (VP8LHistogram*)memory;
+  // literal_ won't necessary be aligned.
+  histo->literal_ = (uint32_t*)(memory + sizeof(VP8LHistogram));
+  VP8LHistogramInit(histo, cache_bits);
+  return histo;
+}
+
 VP8LHistogramSet* VP8LAllocateHistogramSet(int size, int cache_bits) {
   int i;
   VP8LHistogramSet* set;
-  VP8LHistogram* bulk;
-  const uint64_t total_size = (uint64_t)sizeof(*set)
-                            + size * sizeof(*set->histograms)
-                            + size * sizeof(**set->histograms);
+  const int histo_size = VP8LGetHistogramSize(cache_bits);
+  const size_t total_size =
+      sizeof(*set) + size * (sizeof(*set->histograms) +
+      histo_size + WEBP_ALIGN_CST);
   uint8_t* memory = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*memory));
   if (memory == NULL) return NULL;
 
@@ -65,12 +121,15 @@ VP8LHistogramSet* VP8LAllocateHistogramSet(int size, int cache_bits) {
   memory += sizeof(*set);
   set->histograms = (VP8LHistogram**)memory;
   memory += size * sizeof(*set->histograms);
-  bulk = (VP8LHistogram*)memory;
   set->max_size = size;
   set->size = size;
   for (i = 0; i < size; ++i) {
-    set->histograms[i] = bulk + i;
+    memory = (uint8_t*)WEBP_ALIGN(memory);
+    set->histograms[i] = (VP8LHistogram*)memory;
+    // literal_ won't necessary be aligned.
+    set->histograms[i]->literal_ = (uint32_t*)(memory + sizeof(VP8LHistogram));
     VP8LHistogramInit(set->histograms[i], cache_bits);
+    memory += histo_size;
   }
   return set;
 }
@@ -85,151 +144,183 @@ void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
     ++histo->literal_[PixOrCopyLiteral(v, 1)];
     ++histo->blue_[PixOrCopyLiteral(v, 0)];
   } else if (PixOrCopyIsCacheIdx(v)) {
-    int literal_ix = 256 + NUM_LENGTH_CODES + PixOrCopyCacheIdx(v);
+    const int literal_ix =
+        NUM_LITERAL_CODES + NUM_LENGTH_CODES + PixOrCopyCacheIdx(v);
     ++histo->literal_[literal_ix];
   } else {
-    int code, extra_bits_count, extra_bits_value;
-    PrefixEncode(PixOrCopyLength(v),
-                 &code, &extra_bits_count, &extra_bits_value);
-    ++histo->literal_[256 + code];
-    PrefixEncode(PixOrCopyDistance(v),
-                 &code, &extra_bits_count, &extra_bits_value);
+    int code, extra_bits;
+    VP8LPrefixEncodeBits(PixOrCopyLength(v), &code, &extra_bits);
+    ++histo->literal_[NUM_LITERAL_CODES + code];
+    VP8LPrefixEncodeBits(PixOrCopyDistance(v), &code, &extra_bits);
     ++histo->distance_[code];
   }
 }
 
+// -----------------------------------------------------------------------------
+// Various histogram combine/cost-eval functions
+
+static int GetCombinedHistogramEntropy(const VP8LHistogram* const a,
+                                       const VP8LHistogram* const b,
+                                       double cost_threshold,
+                                       double* cost) {
+  const int palette_code_bits = a->palette_code_bits_;
+  assert(a->palette_code_bits_ == b->palette_code_bits_);
+  *cost += VP8LGetCombinedEntropy(a->literal_, b->literal_,
+                                  VP8LHistogramNumCodes(palette_code_bits));
+  *cost += VP8LExtraCostCombined(a->literal_ + NUM_LITERAL_CODES,
+                                 b->literal_ + NUM_LITERAL_CODES,
+                                 NUM_LENGTH_CODES);
+  if (*cost > cost_threshold) return 0;
+
+  *cost += VP8LGetCombinedEntropy(a->red_, b->red_, NUM_LITERAL_CODES);
+  if (*cost > cost_threshold) return 0;
+
+  *cost += VP8LGetCombinedEntropy(a->blue_, b->blue_, NUM_LITERAL_CODES);
+  if (*cost > cost_threshold) return 0;
+
+  *cost += VP8LGetCombinedEntropy(a->alpha_, b->alpha_, NUM_LITERAL_CODES);
+  if (*cost > cost_threshold) return 0;
+
+  *cost += VP8LGetCombinedEntropy(a->distance_, b->distance_,
+                                  NUM_DISTANCE_CODES);
+  *cost += VP8LExtraCostCombined(a->distance_, b->distance_,
+                                 NUM_DISTANCE_CODES);
+  if (*cost > cost_threshold) return 0;
+
+  return 1;
+}
 
-
-static double BitsEntropy(const int* const array, int n) {
-  double retval = 0.;
-  int sum = 0;
-  int nonzeros = 0;
-  int max_val = 0;
-  int i;
-  double mix;
-  for (i = 0; i < n; ++i) {
-    if (array[i] != 0) {
-      sum += array[i];
-      ++nonzeros;
-      retval -= VP8LFastSLog2(array[i]);
-      if (max_val < array[i]) {
-        max_val = array[i];
-      }
-    }
+// Performs out = a + b, computing the cost C(a+b) - C(a) - C(b) while comparing
+// to the threshold value 'cost_threshold'. The score returned is
+//  Score = C(a+b) - C(a) - C(b), where C(a) + C(b) is known and fixed.
+// Since the previous score passed is 'cost_threshold', we only need to compare
+// the partial cost against 'cost_threshold + C(a) + C(b)' to possibly bail-out
+// early.
+static double HistogramAddEval(const VP8LHistogram* const a,
+                               const VP8LHistogram* const b,
+                               VP8LHistogram* const out,
+                               double cost_threshold) {
+  double cost = 0;
+  const double sum_cost = a->bit_cost_ + b->bit_cost_;
+  cost_threshold += sum_cost;
+
+  if (GetCombinedHistogramEntropy(a, b, cost_threshold, &cost)) {
+    VP8LHistogramAdd(a, b, out);
+    out->bit_cost_ = cost;
+    out->palette_code_bits_ = a->palette_code_bits_;
+    out->trivial_symbol_ = (a->trivial_symbol_ == b->trivial_symbol_) ?
+        a->trivial_symbol_ : VP8L_NON_TRIVIAL_SYM;
   }
-  retval += VP8LFastSLog2(sum);
 
-  if (nonzeros < 5) {
-    if (nonzeros <= 1) {
-      return 0;
-    }
-    // Two symbols, they will be 0 and 1 in a Huffman code.
-    // Let's mix in a bit of entropy to favor good clustering when
-    // distributions of these are combined.
-    if (nonzeros == 2) {
-      return 0.99 * sum + 0.01 * retval;
-    }
-    // No matter what the entropy says, we cannot be better than min_limit
-    // with Huffman coding. I am mixing a bit of entropy into the
-    // min_limit since it produces much better (~0.5 %) compression results
-    // perhaps because of better entropy clustering.
-    if (nonzeros == 3) {
-      mix = 0.95;
-    } else {
-      mix = 0.7;  // nonzeros == 4.
-    }
-  } else {
-    mix = 0.627;
-  }
+  return cost - sum_cost;
+}
 
-  {
-    double min_limit = 2 * sum - max_val;
-    min_limit = mix * min_limit + (1.0 - mix) * retval;
-    return (retval < min_limit) ? min_limit : retval;
-  }
+// Same as HistogramAddEval(), except that the resulting histogram
+// is not stored. Only the cost C(a+b) - C(a) is evaluated. We omit
+// the term C(b) which is constant over all the evaluations.
+static double HistogramAddThresh(const VP8LHistogram* const a,
+                                 const VP8LHistogram* const b,
+                                 double cost_threshold) {
+  double cost = -a->bit_cost_;
+  GetCombinedHistogramEntropy(a, b, cost_threshold, &cost);
+  return cost;
 }
 
-double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p) {
-  double retval = BitsEntropy(&p->literal_[0], VP8LHistogramNumCodes(p))
-                + BitsEntropy(&p->red_[0], 256)
-                + BitsEntropy(&p->blue_[0], 256)
-                + BitsEntropy(&p->alpha_[0], 256)
-                + BitsEntropy(&p->distance_[0], NUM_DISTANCE_CODES);
-  // Compute the extra bits cost.
-  int i;
-  for (i = 2; i < NUM_LENGTH_CODES - 2; ++i) {
-    retval +=
-        (i >> 1) * p->literal_[256 + i + 2];
-  }
-  for (i = 2; i < NUM_DISTANCE_CODES - 2; ++i) {
-    retval += (i >> 1) * p->distance_[i + 2];
-  }
-  return retval;
-}
-
-
-// Returns the cost encode the rle-encoded entropy code.
-// The constants in this function are experimental.
-static double HuffmanCost(const int* const population, int length) {
-  // Small bias because Huffman code length is typically not stored in
-  // full length.
-  static const int kHuffmanCodeOfHuffmanCodeSize = CODE_LENGTH_CODES * 3;
-  static const double kSmallBias = 9.1;
-  double retval = kHuffmanCodeOfHuffmanCodeSize - kSmallBias;
-  int streak = 0;
-  int i = 0;
-  for (; i < length - 1; ++i) {
-    ++streak;
-    if (population[i] == population[i + 1]) {
-      continue;
-    }
- last_streak_hack:
-    // population[i] points now to the symbol in the streak of same values.
-    if (streak > 3) {
-      if (population[i] == 0) {
-        retval += 1.5625 + 0.234375 * streak;
-      } else {
-        retval += 2.578125 + 0.703125 * streak;
-      }
-    } else {
-      if (population[i] == 0) {
-        retval += 1.796875 * streak;
-      } else {
-        retval += 3.28125 * streak;
-      }
-    }
-    streak = 0;
-  }
-  if (i == length - 1) {
-    ++streak;
-    goto last_streak_hack;
+// -----------------------------------------------------------------------------
+
+// The structure to keep track of cost range for the three dominant entropy
+// symbols.
+// TODO(skal): Evaluate if float can be used here instead of double for
+// representing the entropy costs.
+typedef struct {
+  double literal_max_;
+  double literal_min_;
+  double red_max_;
+  double red_min_;
+  double blue_max_;
+  double blue_min_;
+} DominantCostRange;
+
+static void DominantCostRangeInit(DominantCostRange* const c) {
+  c->literal_max_ = 0.;
+  c->literal_min_ = MAX_COST;
+  c->red_max_ = 0.;
+  c->red_min_ = MAX_COST;
+  c->blue_max_ = 0.;
+  c->blue_min_ = MAX_COST;
+}
+
+static void UpdateDominantCostRange(
+    const VP8LHistogram* const h, DominantCostRange* const c) {
+  if (c->literal_max_ < h->literal_cost_) c->literal_max_ = h->literal_cost_;
+  if (c->literal_min_ > h->literal_cost_) c->literal_min_ = h->literal_cost_;
+  if (c->red_max_ < h->red_cost_) c->red_max_ = h->red_cost_;
+  if (c->red_min_ > h->red_cost_) c->red_min_ = h->red_cost_;
+  if (c->blue_max_ < h->blue_cost_) c->blue_max_ = h->blue_cost_;
+  if (c->blue_min_ > h->blue_cost_) c->blue_min_ = h->blue_cost_;
+}
+
+static void UpdateHistogramCost(VP8LHistogram* const h) {
+  uint32_t alpha_sym, red_sym, blue_sym;
+  const double alpha_cost = VP8LPopulationCost(h->alpha_, NUM_LITERAL_CODES,
+                                               &alpha_sym);
+  const double distance_cost =
+      VP8LPopulationCost(h->distance_, NUM_DISTANCE_CODES, NULL) +
+      VP8LExtraCost(h->distance_, NUM_DISTANCE_CODES);
+  const int num_codes = VP8LHistogramNumCodes(h->palette_code_bits_);
+  h->literal_cost_ = VP8LPopulationCost(h->literal_, num_codes, NULL) +
+                     VP8LExtraCost(h->literal_ + NUM_LITERAL_CODES,
+                                   NUM_LENGTH_CODES);
+  h->red_cost_ = VP8LPopulationCost(h->red_, NUM_LITERAL_CODES, &red_sym);
+  h->blue_cost_ = VP8LPopulationCost(h->blue_, NUM_LITERAL_CODES, &blue_sym);
+  h->bit_cost_ = h->literal_cost_ + h->red_cost_ + h->blue_cost_ +
+                 alpha_cost + distance_cost;
+  if ((alpha_sym | red_sym | blue_sym) == VP8L_NON_TRIVIAL_SYM) {
+    h->trivial_symbol_ = VP8L_NON_TRIVIAL_SYM;
+  } else {
+    h->trivial_symbol_ =
+        ((uint32_t)alpha_sym << 24) | (red_sym << 16) | (blue_sym << 0);
   }
-  return retval;
 }
 
-// Estimates the Huffman dictionary + other block overhead size.
-static double HistogramEstimateBitsHeader(const VP8LHistogram* const p) {
-  return HuffmanCost(&p->alpha_[0], 256) +
-         HuffmanCost(&p->red_[0], 256) +
-         HuffmanCost(&p->literal_[0], VP8LHistogramNumCodes(p)) +
-         HuffmanCost(&p->blue_[0], 256) +
-         HuffmanCost(&p->distance_[0], NUM_DISTANCE_CODES);
+static int GetBinIdForEntropy(double min, double max, double val) {
+  const double range = max - min + 1e-6;
+  const double delta = val - min;
+  return (int)(NUM_PARTITIONS * delta / range);
 }
 
-double VP8LHistogramEstimateBits(const VP8LHistogram* const p) {
-  return HistogramEstimateBitsHeader(p) + VP8LHistogramEstimateBitsBulk(p);
+static int GetHistoBinIndexLowEffort(
+    const VP8LHistogram* const h, const DominantCostRange* const c) {
+  const int bin_id = GetBinIdForEntropy(c->literal_min_, c->literal_max_,
+                                        h->literal_cost_);
+  assert(bin_id < NUM_PARTITIONS);
+  return bin_id;
 }
 
-static void HistogramBuildImage(int xsize, int histo_bits,
-                                const VP8LBackwardRefs* const backward_refs,
-                                VP8LHistogramSet* const image) {
-  int i;
+static int GetHistoBinIndex(
+    const VP8LHistogram* const h, const DominantCostRange* const c) {
+  const int bin_id =
+      GetBinIdForEntropy(c->blue_min_, c->blue_max_, h->blue_cost_) +
+      NUM_PARTITIONS * GetBinIdForEntropy(c->red_min_, c->red_max_,
+                                          h->red_cost_) +
+      NUM_PARTITIONS * NUM_PARTITIONS * GetBinIdForEntropy(c->literal_min_,
+                                                           c->literal_max_,
+                                                           h->literal_cost_);
+  assert(bin_id < BIN_SIZE);
+  return bin_id;
+}
+
+// Construct the histograms from backward references.
+static void HistogramBuild(
+    int xsize, int histo_bits, const VP8LBackwardRefs* const backward_refs,
+    VP8LHistogramSet* const image_histo) {
   int x = 0, y = 0;
   const int histo_xsize = VP8LSubSampleSize(xsize, histo_bits);
-  VP8LHistogram** const histograms = image->histograms;
+  VP8LHistogram** const histograms = image_histo->histograms;
+  VP8LRefsCursor c = VP8LRefsCursorInit(backward_refs);
   assert(histo_bits > 0);
-  for (i = 0; i < backward_refs->size; ++i) {
-    const PixOrCopy* const v = &backward_refs->refs[i];
+  while (VP8LRefsCursorOk(&c)) {
+    const PixOrCopy* const v = c.cur_pos;
     const int ix = (y >> histo_bits) * histo_xsize + (x >> histo_bits);
     VP8LHistogramAddSinglePixOrCopy(histograms[ix], v);
     x += PixOrCopyLength(v);
@@ -237,7 +328,134 @@ static void HistogramBuildImage(int xsize, int histo_bits,
       x -= xsize;
       ++y;
     }
+    VP8LRefsCursorNext(&c);
+  }
+}
+
+// Copies the histograms and computes its bit_cost.
+static void HistogramCopyAndAnalyze(
+    VP8LHistogramSet* const orig_histo, VP8LHistogramSet* const image_histo) {
+  int i;
+  const int histo_size = orig_histo->size;
+  VP8LHistogram** const orig_histograms = orig_histo->histograms;
+  VP8LHistogram** const histograms = image_histo->histograms;
+  for (i = 0; i < histo_size; ++i) {
+    VP8LHistogram* const histo = orig_histograms[i];
+    UpdateHistogramCost(histo);
+    // Copy histograms from orig_histo[] to image_histo[].
+    HistogramCopy(histo, histograms[i]);
+  }
+}
+
+// Partition histograms to different entropy bins for three dominant (literal,
+// red and blue) symbol costs and compute the histogram aggregate bit_cost.
+static void HistogramAnalyzeEntropyBin(VP8LHistogramSet* const image_histo,
+                                       int16_t* const bin_map, int low_effort) {
+  int i;
+  VP8LHistogram** const histograms = image_histo->histograms;
+  const int histo_size = image_histo->size;
+  const int bin_depth = histo_size + 1;
+  DominantCostRange cost_range;
+  DominantCostRangeInit(&cost_range);
+
+  // Analyze the dominant (literal, red and blue) entropy costs.
+  for (i = 0; i < histo_size; ++i) {
+    VP8LHistogram* const histo = histograms[i];
+    UpdateDominantCostRange(histo, &cost_range);
+  }
+
+  // bin-hash histograms on three of the dominant (literal, red and blue)
+  // symbol costs.
+  for (i = 0; i < histo_size; ++i) {
+    int num_histos;
+    VP8LHistogram* const histo = histograms[i];
+    const int16_t bin_id = low_effort ?
+        (int16_t)GetHistoBinIndexLowEffort(histo, &cost_range) :
+        (int16_t)GetHistoBinIndex(histo, &cost_range);
+    const int bin_offset = bin_id * bin_depth;
+    // bin_map[n][0] for every bin 'n' maintains the counter for the number of
+    // histograms in that bin.
+    // Get and increment the num_histos in that bin.
+    num_histos = ++bin_map[bin_offset];
+    assert(bin_offset + num_histos < bin_depth * BIN_SIZE);
+    // Add histogram i'th index at num_histos (last) position in the bin_map.
+    bin_map[bin_offset + num_histos] = i;
+  }
+}
+
+// Compact the histogram set by removing unused entries.
+static void HistogramCompactBins(VP8LHistogramSet* const image_histo) {
+  VP8LHistogram** const histograms = image_histo->histograms;
+  int i, j;
+
+  for (i = 0, j = 0; i < image_histo->size; ++i) {
+    if (histograms[i] != NULL && histograms[i]->bit_cost_ != 0.) {
+      if (j < i) {
+        histograms[j] = histograms[i];
+        histograms[i] = NULL;
+      }
+      ++j;
+    }
   }
+  image_histo->size = j;
+}
+
+static VP8LHistogram* HistogramCombineEntropyBin(
+    VP8LHistogramSet* const image_histo,
+    VP8LHistogram* cur_combo,
+    int16_t* const bin_map, int bin_depth, int num_bins,
+    double combine_cost_factor, int low_effort) {
+  int bin_id;
+  VP8LHistogram** const histograms = image_histo->histograms;
+
+  for (bin_id = 0; bin_id < num_bins; ++bin_id) {
+    const int bin_offset = bin_id * bin_depth;
+    const int num_histos = bin_map[bin_offset];
+    const int idx1 = bin_map[bin_offset + 1];
+    int num_combine_failures = 0;
+    int n;
+    for (n = 2; n <= num_histos; ++n) {
+      const int idx2 = bin_map[bin_offset + n];
+      if (low_effort) {
+        // Merge all histograms with the same bin index, irrespective of cost of
+        // the merged histograms.
+        VP8LHistogramAdd(histograms[idx1], histograms[idx2], histograms[idx1]);
+        histograms[idx2]->bit_cost_ = 0.;
+      } else {
+        const double bit_cost_idx2 = histograms[idx2]->bit_cost_;
+        if (bit_cost_idx2 > 0.) {
+          const double bit_cost_thresh = -bit_cost_idx2 * combine_cost_factor;
+          const double curr_cost_diff =
+              HistogramAddEval(histograms[idx1], histograms[idx2],
+                               cur_combo, bit_cost_thresh);
+          if (curr_cost_diff < bit_cost_thresh) {
+            // Try to merge two histograms only if the combo is a trivial one or
+            // the two candidate histograms are already non-trivial.
+            // For some images, 'try_combine' turns out to be false for a lot of
+            // histogram pairs. In that case, we fallback to combining
+            // histograms as usual to avoid increasing the header size.
+            const int try_combine =
+                (cur_combo->trivial_symbol_ != VP8L_NON_TRIVIAL_SYM) ||
+                ((histograms[idx1]->trivial_symbol_ == VP8L_NON_TRIVIAL_SYM) &&
+                 (histograms[idx2]->trivial_symbol_ == VP8L_NON_TRIVIAL_SYM));
+            const int max_combine_failures = 32;
+            if (try_combine || (num_combine_failures >= max_combine_failures)) {
+              HistogramSwap(&cur_combo, &histograms[idx1]);
+              histograms[idx2]->bit_cost_ = 0.;
+            } else {
+              ++num_combine_failures;
+            }
+          }
+        }
+      }
+    }
+    if (low_effort) {
+      // Update the bit_cost for the merged histograms (per bin index).
+      UpdateHistogramCost(histograms[idx1]);
+    }
+  }
+  HistogramCompactBins(image_histo);
+  return cur_combo;
 }
 
 static uint32_t MyRand(uint32_t *seed) {
@@ -248,159 +466,433 @@ static uint32_t MyRand(uint32_t *seed) {
   return *seed;
 }
 
-static int HistogramCombine(const VP8LHistogramSet* const in,
-                            VP8LHistogramSet* const out, int num_pairs) {
+// -----------------------------------------------------------------------------
+// Histogram pairs priority queue
+
+// Pair of histograms. Negative idx1 value means that pair is out-of-date.
+typedef struct {
+  int idx1;
+  int idx2;
+  double cost_diff;
+  double cost_combo;
+} HistogramPair;
+
+typedef struct {
+  HistogramPair* heap;
+  int* positions;
+  int size;
+  int max_index;
+} HistoHeap;
+
+static int HistoHeapInit(HistoHeap* const histo_heap, const int max_index) {
+  histo_heap->size = 0;
+  histo_heap->max_index = max_index;
+  histo_heap->heap = WebPSafeMalloc(max_index * max_index,
+                                    sizeof(*histo_heap->heap));
+  histo_heap->positions = WebPSafeMalloc(max_index * max_index,
+                                         sizeof(*histo_heap->positions));
+  return histo_heap->heap != NULL && histo_heap->positions != NULL;
+}
+
+static void HistoHeapClear(HistoHeap* const histo_heap) {
+  assert(histo_heap != NULL);
+  WebPSafeFree(histo_heap->heap);
+  WebPSafeFree(histo_heap->positions);
+}
+
+static void SwapHistogramPairs(HistogramPair *p1,
+                               HistogramPair *p2) {
+  const HistogramPair tmp = *p1;
+  *p1 = *p2;
+  *p2 = tmp;
+}
+
+// Given a valid min-heap in range [0, heap_size-1) this function places value
+// heap[heap_size-1] into right location within heap and sets its position in
+// positions array.
+static void HeapPush(HistoHeap* const histo_heap) {
+  HistogramPair* const heap = histo_heap->heap - 1;
+  int* const positions = histo_heap->positions;
+  const int max_index = histo_heap->max_index;
+  int v;
+  ++histo_heap->size;
+  v = histo_heap->size;
+  while (v > 1 && heap[v].cost_diff < heap[v >> 1].cost_diff) {
+    SwapHistogramPairs(&heap[v], &heap[v >> 1]);
+    // Change position of moved pair in heap.
+    if (heap[v].idx1 >= 0) {
+      const int pos = heap[v].idx1 * max_index + heap[v].idx2;
+      assert(pos >= 0 && pos < max_index * max_index);
+      positions[pos] = v;
+    }
+    v >>= 1;
+  }
+  positions[heap[v].idx1 * max_index + heap[v].idx2] = v;
+}
+
+// Given a valid min-heap in range [0, heap_size) this function shortens heap
+// range by one and places element with the lowest value to (heap_size-1).
+static void HeapPop(HistoHeap* const histo_heap) {
+  HistogramPair* const heap = histo_heap->heap - 1;
+  int* const positions = histo_heap->positions;
+  const int heap_size = histo_heap->size;
+  const int max_index = histo_heap->max_index;
+  int v = 1;
+  if (heap[v].idx1 >= 0) {
+    positions[heap[v].idx1 * max_index + heap[v].idx2] = -1;
+  }
+  SwapHistogramPairs(&heap[v], &heap[heap_size]);
+  while ((v << 1) < heap_size) {
+    int son = (heap[v << 1].cost_diff < heap[v].cost_diff) ? (v << 1) : v;
+    if (((v << 1) + 1) < heap_size &&
+        heap[(v << 1) + 1].cost_diff < heap[son].cost_diff) {
+      son = (v << 1) + 1;
+    }
+    if (son == v) break;
+    SwapHistogramPairs(&heap[v], &heap[son]);
+    // Change position of moved pair in heap.
+    if (heap[v].idx1 >= 0) {
+      positions[heap[v].idx1 * max_index + heap[v].idx2] = v;
+    }
+    v = son;
+  }
+  if (heap[v].idx1 >= 0) {
+    positions[heap[v].idx1 * max_index + heap[v].idx2] = v;
+  }
+  --histo_heap->size;
+}
+
+// -----------------------------------------------------------------------------
+
+static void PreparePair(VP8LHistogram** histograms, int idx1, int idx2,
+                        HistogramPair* const pair,
+                        VP8LHistogram* const histos) {
+  if (idx1 > idx2) {
+    const int tmp = idx2;
+    idx2 = idx1;
+    idx1 = tmp;
+  }
+  pair->idx1 = idx1;
+  pair->idx2 = idx2;
+  pair->cost_diff =
+      HistogramAddEval(histograms[idx1], histograms[idx2], histos, 0);
+  pair->cost_combo = histos->bit_cost_;
+}
+
+#define POSITION_INVALID (-1)
+
+// Invalidates pairs intersecting (idx1, idx2) in heap.
+static void InvalidatePairs(int idx1, int idx2,
+                            const HistoHeap* const histo_heap) {
+  HistogramPair* const heap = histo_heap->heap - 1;
+  int* const positions = histo_heap->positions;
+  const int max_index = histo_heap->max_index;
+  int i;
+  for (i = 0; i < idx1; ++i) {
+    const int pos = positions[i * max_index + idx1];
+    if (pos >= 0) {
+      heap[pos].idx1 = POSITION_INVALID;
+    }
+  }
+  for (i = idx1 + 1; i < max_index; ++i) {
+    const int pos = positions[idx1 * max_index + i];
+    if (pos >= 0) {
+      heap[pos].idx1 = POSITION_INVALID;
+    }
+  }
+  for (i = 0; i < idx2; ++i) {
+    const int pos = positions[i * max_index + idx2];
+    if (pos >= 0) {
+      heap[pos].idx1 = POSITION_INVALID;
+    }
+  }
+  for (i = idx2 + 1; i < max_index; ++i) {
+    const int pos = positions[idx2 * max_index + i];
+    if (pos >= 0) {
+      heap[pos].idx1 = POSITION_INVALID;
+    }
+  }
+}
+
+// Combines histograms by continuously choosing the one with the highest cost
+// reduction.
+static int HistogramCombineGreedy(VP8LHistogramSet* const image_histo,
+                                  VP8LHistogram* const histos) {
   int ok = 0;
-  int i, iter;
+  int image_histo_size = image_histo->size;
+  int i, j;
+  VP8LHistogram** const histograms = image_histo->histograms;
+  // Indexes of remaining histograms.
+  int* const clusters = WebPSafeMalloc(image_histo_size, sizeof(*clusters));
+  // Heap of histogram pairs.
+  HistoHeap histo_heap;
+
+  if (!HistoHeapInit(&histo_heap, image_histo_size) || clusters == NULL) {
+    goto End;
+  }
+
+  for (i = 0; i < image_histo_size; ++i) {
+    // Initialize clusters indexes.
+    clusters[i] = i;
+    for (j = i + 1; j < image_histo_size; ++j) {
+      // Initialize positions array.
+      histo_heap.positions[i * histo_heap.max_index + j] = POSITION_INVALID;
+      PreparePair(histograms, i, j, &histo_heap.heap[histo_heap.size], histos);
+      if (histo_heap.heap[histo_heap.size].cost_diff < 0) {
+        HeapPush(&histo_heap);
+      }
+    }
+  }
+
+  while (image_histo_size > 1 && histo_heap.size > 0) {
+    const int idx1 = histo_heap.heap[0].idx1;
+    const int idx2 = histo_heap.heap[0].idx2;
+    VP8LHistogramAdd(histograms[idx2], histograms[idx1], histograms[idx1]);
+    histograms[idx1]->bit_cost_ = histo_heap.heap[0].cost_combo;
+    // Remove merged histogram.
+    for (i = 0; i + 1 < image_histo_size; ++i) {
+      if (clusters[i] >= idx2) {
+        clusters[i] = clusters[i + 1];
+      }
+    }
+    --image_histo_size;
+
+    // Invalidate pairs intersecting the just combined best pair.
+    InvalidatePairs(idx1, idx2, &histo_heap);
+
+    // Pop invalid pairs from the top of the heap.
+    while (histo_heap.size > 0 && histo_heap.heap[0].idx1 < 0) {
+      HeapPop(&histo_heap);
+    }
+
+    // Push new pairs formed with combined histogram to the heap.
+    for (i = 0; i < image_histo_size; ++i) {
+      if (clusters[i] != idx1) {
+        PreparePair(histograms, idx1, clusters[i],
+                    &histo_heap.heap[histo_heap.size], histos);
+        if (histo_heap.heap[histo_heap.size].cost_diff < 0) {
+          HeapPush(&histo_heap);
+        }
+      }
+    }
+  }
+  // Move remaining histograms to the beginning of the array.
+  for (i = 0; i < image_histo_size; ++i) {
+    if (i != clusters[i]) {  // swap the two histograms
+      HistogramSwap(&histograms[i], &histograms[clusters[i]]);
+    }
+  }
+
+  image_histo->size = image_histo_size;
+  ok = 1;
+
+ End:
+  WebPSafeFree(clusters);
+  HistoHeapClear(&histo_heap);
+  return ok;
+}
+
+static VP8LHistogram* HistogramCombineStochastic(
+    VP8LHistogramSet* const image_histo,
+    VP8LHistogram* tmp_histo,
+    VP8LHistogram* best_combo,
+    int quality, int min_cluster_size) {
+  int iter;
   uint32_t seed = 0;
   int tries_with_no_success = 0;
-  const int min_cluster_size = 2;
-  int out_size = in->size;
-  const int outer_iters = in->size * 3;
-  VP8LHistogram* const histos = (VP8LHistogram*)malloc(2 * sizeof(*histos));
-  VP8LHistogram* cur_combo = histos + 0;    // trial merged histogram
-  VP8LHistogram* best_combo = histos + 1;   // best merged histogram so far
-  if (histos == NULL) goto End;
-
-  // Copy histograms from in[] to out[].
-  assert(in->size <= out->size);
-  for (i = 0; i < in->size; ++i) {
-    in->histograms[i]->bit_cost_ = VP8LHistogramEstimateBits(in->histograms[i]);
-    *out->histograms[i] = *in->histograms[i];
-  }
-
-  // Collapse similar histograms in 'out'.
-  for (iter = 0; iter < outer_iters && out_size >= min_cluster_size; ++iter) {
-    // We pick the best pair to be combined out of 'inner_iters' pairs.
+  int image_histo_size = image_histo->size;
+  const int iter_mult = (quality < 25) ? 2 : 2 + (quality - 25) / 8;
+  const int outer_iters = image_histo_size * iter_mult;
+  const int num_pairs = image_histo_size / 2;
+  const int num_tries_no_success = outer_iters / 2;
+  VP8LHistogram** const histograms = image_histo->histograms;
+
+  // Collapse similar histograms in 'image_histo'.
+  ++min_cluster_size;
+  for (iter = 0;
+       iter < outer_iters && image_histo_size >= min_cluster_size;
+       ++iter) {
     double best_cost_diff = 0.;
-    int best_idx1 = 0, best_idx2 = 1;
+    int best_idx1 = -1, best_idx2 = 1;
     int j;
+    const int num_tries =
+        (num_pairs < image_histo_size) ? num_pairs : image_histo_size;
     seed += iter;
-    for (j = 0; j < num_pairs; ++j) {
+    for (j = 0; j < num_tries; ++j) {
       double curr_cost_diff;
       // Choose two histograms at random and try to combine them.
-      const uint32_t idx1 = MyRand(&seed) % out_size;
-      const uint32_t tmp = ((j & 7) + 1) % (out_size - 1);
-      const uint32_t diff = (tmp < 3) ? tmp : MyRand(&seed) % (out_size - 1);
-      const uint32_t idx2 = (idx1 + diff + 1) % out_size;
+      const uint32_t idx1 = MyRand(&seed) % image_histo_size;
+      const uint32_t tmp = (j & 7) + 1;
+      const uint32_t diff =
+          (tmp < 3) ? tmp : MyRand(&seed) % (image_histo_size - 1);
+      const uint32_t idx2 = (idx1 + diff + 1) % image_histo_size;
       if (idx1 == idx2) {
         continue;
       }
-      *cur_combo = *out->histograms[idx1];
-      VP8LHistogramAdd(cur_combo, out->histograms[idx2]);
-      cur_combo->bit_cost_ = VP8LHistogramEstimateBits(cur_combo);
+
       // Calculate cost reduction on combining.
-      curr_cost_diff = cur_combo->bit_cost_
-                     - out->histograms[idx1]->bit_cost_
-                     - out->histograms[idx2]->bit_cost_;
-      if (best_cost_diff > curr_cost_diff) {    // found a better pair?
-        {     // swap cur/best combo histograms
-          VP8LHistogram* const tmp_histo = cur_combo;
-          cur_combo = best_combo;
-          best_combo = tmp_histo;
-        }
+      curr_cost_diff = HistogramAddEval(histograms[idx1], histograms[idx2],
+                                        tmp_histo, best_cost_diff);
+      if (curr_cost_diff < best_cost_diff) {    // found a better pair?
+        HistogramSwap(&best_combo, &tmp_histo);
         best_cost_diff = curr_cost_diff;
         best_idx1 = idx1;
         best_idx2 = idx2;
       }
     }
 
-    if (best_cost_diff < 0.0) {
-      *out->histograms[best_idx1] = *best_combo;
+    if (best_idx1 >= 0) {
+      HistogramSwap(&best_combo, &histograms[best_idx1]);
       // swap best_idx2 slot with last one (which is now unused)
-      --out_size;
-      if (best_idx2 != out_size) {
-        out->histograms[best_idx2] = out->histograms[out_size];
-        out->histograms[out_size] = NULL;   // just for sanity check.
+      --image_histo_size;
+      if (best_idx2 != image_histo_size) {
+        HistogramSwap(&histograms[image_histo_size], &histograms[best_idx2]);
+        histograms[image_histo_size] = NULL;
       }
       tries_with_no_success = 0;
     }
-    if (++tries_with_no_success >= 50) {
+    if (++tries_with_no_success >= num_tries_no_success) {
       break;
     }
   }
-  out->size = out_size;
-  ok = 1;
-
- End:
-  free(histos);
-  return ok;
+  image_histo->size = image_histo_size;
+  return best_combo;
 }
 
 // -----------------------------------------------------------------------------
 // Histogram refinement
 
-// What is the bit cost of moving square_histogram from
-// cur_symbol to candidate_symbol.
-// TODO(skal): we don't really need to copy the histogram and Add(). Instead
-// we just need VP8LDualHistogramEstimateBits(A, B) estimation function.
-static double HistogramDistance(const VP8LHistogram* const square_histogram,
-                                const VP8LHistogram* const candidate) {
-  const double previous_bit_cost = candidate->bit_cost_;
-  double new_bit_cost;
-  VP8LHistogram modified_histo;
-  modified_histo = *candidate;
-  VP8LHistogramAdd(&modified_histo, square_histogram);
-  new_bit_cost = VP8LHistogramEstimateBits(&modified_histo);
-
-  return new_bit_cost - previous_bit_cost;
-}
-
 // Find the best 'out' histogram for each of the 'in' histograms.
 // Note: we assume that out[]->bit_cost_ is already up-to-date.
-static void HistogramRemap(const VP8LHistogramSet* const in,
-                           const VP8LHistogramSet* const out,
+static void HistogramRemap(const VP8LHistogramSet* const orig_histo,
+                           const VP8LHistogramSet* const image_histo,
                            uint16_t* const symbols) {
   int i;
-  for (i = 0; i < in->size; ++i) {
-    int best_out = 0;
-    double best_bits = HistogramDistance(in->histograms[i], out->histograms[0]);
-    int k;
-    for (k = 1; k < out->size; ++k) {
-      const double cur_bits =
-          HistogramDistance(in->histograms[i], out->histograms[k]);
-      if (cur_bits < best_bits) {
-        best_bits = cur_bits;
-        best_out = k;
+  VP8LHistogram** const orig_histograms = orig_histo->histograms;
+  VP8LHistogram** const histograms = image_histo->histograms;
+  const int orig_histo_size = orig_histo->size;
+  const int image_histo_size = image_histo->size;
+  if (image_histo_size > 1) {
+    for (i = 0; i < orig_histo_size; ++i) {
+      int best_out = 0;
+      double best_bits =
+          HistogramAddThresh(histograms[0], orig_histograms[i], MAX_COST);
+      int k;
+      for (k = 1; k < image_histo_size; ++k) {
+        const double cur_bits =
+            HistogramAddThresh(histograms[k], orig_histograms[i], best_bits);
+        if (cur_bits < best_bits) {
+          best_bits = cur_bits;
+          best_out = k;
+        }
       }
+      symbols[i] = best_out;
+    }
+  } else {
+    assert(image_histo_size == 1);
+    for (i = 0; i < orig_histo_size; ++i) {
+      symbols[i] = 0;
     }
-    symbols[i] = best_out;
   }
 
   // Recompute each out based on raw and symbols.
-  for (i = 0; i < out->size; ++i) {
-    HistogramClear(out->histograms[i]);
+  for (i = 0; i < image_histo_size; ++i) {
+    HistogramClear(histograms[i]);
   }
-  for (i = 0; i < in->size; ++i) {
-    VP8LHistogramAdd(out->histograms[symbols[i]], in->histograms[i]);
+
+  for (i = 0; i < orig_histo_size; ++i) {
+    const int idx = symbols[i];
+    VP8LHistogramAdd(orig_histograms[i], histograms[idx], histograms[idx]);
   }
 }
 
+static double GetCombineCostFactor(int histo_size, int quality) {
+  double combine_cost_factor = 0.16;
+  if (quality < 90) {
+    if (histo_size > 256) combine_cost_factor /= 2.;
+    if (histo_size > 512) combine_cost_factor /= 2.;
+    if (histo_size > 1024) combine_cost_factor /= 2.;
+    if (quality <= 50) combine_cost_factor /= 2.;
+  }
+  return combine_cost_factor;
+}
+
 int VP8LGetHistoImageSymbols(int xsize, int ysize,
                              const VP8LBackwardRefs* const refs,
-                             int quality, int histo_bits, int cache_bits,
-                             VP8LHistogramSet* const image_in,
+                             int quality, int low_effort,
+                             int histo_bits, int cache_bits,
+                             VP8LHistogramSet* const image_histo,
+                             VP8LHistogramSet* const tmp_histos,
                              uint16_t* const histogram_symbols) {
   int ok = 0;
   const int histo_xsize = histo_bits ? VP8LSubSampleSize(xsize, histo_bits) : 1;
   const int histo_ysize = histo_bits ? VP8LSubSampleSize(ysize, histo_bits) : 1;
-  const int num_histo_pairs = 10 + quality / 2;  // For HistogramCombine().
-  const int histo_image_raw_size = histo_xsize * histo_ysize;
-  VP8LHistogramSet* const image_out =
-      VP8LAllocateHistogramSet(histo_image_raw_size, cache_bits);
-  if (image_out == NULL) return 0;
-
-  // Build histogram image.
-  HistogramBuildImage(xsize, histo_bits, refs, image_out);
-  // Collapse similar histograms.
-  if (!HistogramCombine(image_out, image_in, num_histo_pairs)) {
-    goto Error;
+  const int image_histo_raw_size = histo_xsize * histo_ysize;
+  const int entropy_combine_num_bins = low_effort ? NUM_PARTITIONS : BIN_SIZE;
+
+  // The bin_map for every bin follows following semantics:
+  // bin_map[n][0] = num_histo; // The number of histograms in that bin.
+  // bin_map[n][1] = index of first histogram in that bin;
+  // bin_map[n][num_histo] = index of last histogram in that bin;
+  // bin_map[n][num_histo + 1] ... bin_map[n][bin_depth - 1] = unused indices.
+  const int bin_depth = image_histo_raw_size + 1;
+  int16_t* bin_map = NULL;
+  VP8LHistogramSet* const orig_histo =
+      VP8LAllocateHistogramSet(image_histo_raw_size, cache_bits);
+  VP8LHistogram* cur_combo;
+  const int entropy_combine =
+      (orig_histo->size > entropy_combine_num_bins * 2) && (quality < 100);
+
+  if (orig_histo == NULL) goto Error;
+
+  // Don't attempt linear bin-partition heuristic for:
+  // histograms of small sizes, as bin_map will be very sparse and;
+  // Maximum quality (q==100), to preserve the compression gains at that level.
+  if (entropy_combine) {
+    const int bin_map_size = bin_depth * entropy_combine_num_bins;
+    bin_map = (int16_t*)WebPSafeCalloc(bin_map_size, sizeof(*bin_map));
+    if (bin_map == NULL) goto Error;
   }
+
+  // Construct the histograms from backward references.
+  HistogramBuild(xsize, histo_bits, refs, orig_histo);
+  // Copies the histograms and computes its bit_cost.
+  HistogramCopyAndAnalyze(orig_histo, image_histo);
+
+  cur_combo = tmp_histos->histograms[1];  // pick up working slot
+  if (entropy_combine) {
+    const double combine_cost_factor =
+        GetCombineCostFactor(image_histo_raw_size, quality);
+    HistogramAnalyzeEntropyBin(orig_histo, bin_map, low_effort);
+    // Collapse histograms with similar entropy.
+    cur_combo = HistogramCombineEntropyBin(image_histo, cur_combo, bin_map,
+                                           bin_depth, entropy_combine_num_bins,
+                                           combine_cost_factor, low_effort);
+  }
+
+  // Don't combine the histograms using stochastic and greedy heuristics for
+  // low-effort compression mode.
+  if (!low_effort || !entropy_combine) {
+    const float x = quality / 100.f;
+    // cubic ramp between 1 and MAX_HISTO_GREEDY:
+    const int threshold_size = (int)(1 + (x * x * x) * (MAX_HISTO_GREEDY - 1));
+    cur_combo = HistogramCombineStochastic(image_histo,
+                                           tmp_histos->histograms[0],
+                                           cur_combo, quality, threshold_size);
+    if ((image_histo->size <= threshold_size) &&
+        !HistogramCombineGreedy(image_histo, cur_combo)) {
+      goto Error;
+    }
+  }
+
+  // TODO(vikasa): Optimize HistogramRemap for low-effort compression mode also.
   // Find the optimal map from original histograms to the final ones.
-  HistogramRemap(image_out, image_in, histogram_symbols);
+  HistogramRemap(orig_histo, image_histo, histogram_symbols);
+
   ok = 1;
 
-Error:
-  free(image_out);
+ Error:
+  WebPSafeFree(bin_map);
+  VP8LFreeHistogramSet(orig_histo);
   return ok;
 }
diff --git a/drivers/webp/enc/histogram.h b/drivers/webp/enc/histogram.h
index 5b5de25539..adb16c01ca 100644
--- a/drivers/webp/enc/histogram.h
+++ b/drivers/webp/enc/histogram.h
@@ -1,8 +1,10 @@
 // Copyright 2012 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Author: Jyrki Alakuijala (jyrki@google.com)
@@ -12,17 +14,13 @@
 #ifndef WEBP_ENC_HISTOGRAM_H_
 #define WEBP_ENC_HISTOGRAM_H_
 
-#include <assert.h>
-#include <stddef.h>
-#include <stdlib.h>
-#include <stdio.h>
 #include <string.h>
 
 #include "./backward_references.h"
-#include "../format_constants.h"
-#include "../types.h"
+#include "../webp/format_constants.h"
+#include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -30,18 +28,23 @@ extern "C" {
 typedef struct {
   // literal_ contains green literal, palette-code and
   // copy-length-prefix histogram
-  int literal_[PIX_OR_COPY_CODES_MAX];
-  int red_[256];
-  int blue_[256];
-  int alpha_[256];
+  uint32_t* literal_;         // Pointer to the allocated buffer for literal.
+  uint32_t red_[NUM_LITERAL_CODES];
+  uint32_t blue_[NUM_LITERAL_CODES];
+  uint32_t alpha_[NUM_LITERAL_CODES];
   // Backward reference prefix-code histogram.
-  int distance_[NUM_DISTANCE_CODES];
+  uint32_t distance_[NUM_DISTANCE_CODES];
   int palette_code_bits_;
-  double bit_cost_;   // cached value of VP8LHistogramEstimateBits(this)
+  uint32_t trivial_symbol_;  // True, if histograms for Red, Blue & Alpha
+                             // literal symbols are single valued.
+  double bit_cost_;          // cached value of bit cost.
+  double literal_cost_;      // Cached values of dominant entropy costs:
+  double red_cost_;          // literal, red & blue.
+  double blue_cost_;
 } VP8LHistogram;
 
 // Collection of histograms with fixed capacity, allocated as one
-// big memory chunk. Can be destroyed by simply calling 'free()'.
+// big memory chunk. Can be destroyed by calling WebPSafeFree().
 typedef struct {
   int size;         // number of slots currently in use
   int max_size;     // maximum capacity
@@ -57,6 +60,9 @@ void VP8LHistogramCreate(VP8LHistogram* const p,
                          const VP8LBackwardRefs* const refs,
                          int palette_code_bits);
 
+// Return the size of the histogram for a given palette_code_bits.
+int VP8LGetHistogramSize(int palette_code_bits);
+
 // Set the palette_code_bits and reset the stats.
 void VP8LHistogramInit(VP8LHistogram* const p, int palette_code_bits);
 
@@ -64,51 +70,40 @@ void VP8LHistogramInit(VP8LHistogram* const p, int palette_code_bits);
 void VP8LHistogramStoreRefs(const VP8LBackwardRefs* const refs,
                             VP8LHistogram* const histo);
 
+// Free the memory allocated for the histogram.
+void VP8LFreeHistogram(VP8LHistogram* const histo);
+
+// Free the memory allocated for the histogram set.
+void VP8LFreeHistogramSet(VP8LHistogramSet* const histo);
+
 // Allocate an array of pointer to histograms, allocated and initialized
 // using 'cache_bits'. Return NULL in case of memory error.
 VP8LHistogramSet* VP8LAllocateHistogramSet(int size, int cache_bits);
 
+// Allocate and initialize histogram object with specified 'cache_bits'.
+// Returns NULL in case of memory error.
+// Special case of VP8LAllocateHistogramSet, with size equals 1.
+VP8LHistogram* VP8LAllocateHistogram(int cache_bits);
+
 // Accumulate a token 'v' into a histogram.
 void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
                                      const PixOrCopy* const v);
 
-// Estimate how many bits the combined entropy of literals and distance
-// approximately maps to.
-double VP8LHistogramEstimateBits(const VP8LHistogram* const p);
-
-// This function estimates the cost in bits excluding the bits needed to
-// represent the entropy code itself.
-double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p);
-
-static WEBP_INLINE void VP8LHistogramAdd(VP8LHistogram* const p,
-                                         const VP8LHistogram* const a) {
-  int i;
-  for (i = 0; i < PIX_OR_COPY_CODES_MAX; ++i) {
-    p->literal_[i] += a->literal_[i];
-  }
-  for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
-    p->distance_[i] += a->distance_[i];
-  }
-  for (i = 0; i < 256; ++i) {
-    p->red_[i] += a->red_[i];
-    p->blue_[i] += a->blue_[i];
-    p->alpha_[i] += a->alpha_[i];
-  }
-}
-
-static WEBP_INLINE int VP8LHistogramNumCodes(const VP8LHistogram* const p) {
-  return 256 + NUM_LENGTH_CODES +
-      ((p->palette_code_bits_ > 0) ? (1 << p->palette_code_bits_) : 0);
+static WEBP_INLINE int VP8LHistogramNumCodes(int palette_code_bits) {
+  return NUM_LITERAL_CODES + NUM_LENGTH_CODES +
+      ((palette_code_bits > 0) ? (1 << palette_code_bits) : 0);
 }
 
 // Builds the histogram image.
 int VP8LGetHistoImageSymbols(int xsize, int ysize,
                              const VP8LBackwardRefs* const refs,
-                             int quality, int histogram_bits, int cache_bits,
+                             int quality, int low_effort,
+                             int histogram_bits, int cache_bits,
                              VP8LHistogramSet* const image_in,
+                             VP8LHistogramSet* const tmp_histos,
                              uint16_t* const histogram_symbols);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/drivers/webp/enc/iterator.c b/drivers/webp/enc/iterator.c
index 86e473bcf0..99d960a547 100644
--- a/drivers/webp/enc/iterator.c
+++ b/drivers/webp/enc/iterator.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // VP8Iterator: block iterator
@@ -13,21 +15,16 @@
 
 #include "./vp8enci.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 //------------------------------------------------------------------------------
 // VP8Iterator
 //------------------------------------------------------------------------------
 
 static void InitLeft(VP8EncIterator* const it) {
-  const VP8Encoder* const enc = it->enc_;
-  enc->y_left_[-1] = enc->u_left_[-1] = enc->v_left_[-1] =
+  it->y_left_[-1] = it->u_left_[-1] = it->v_left_[-1] =
       (it->y_ > 0) ? 129 : 127;
-  memset(enc->y_left_, 129, 16);
-  memset(enc->u_left_, 129, 8);
-  memset(enc->v_left_, 129, 8);
+  memset(it->y_left_, 129, 16);
+  memset(it->u_left_, 129, 8);
+  memset(it->v_left_, 129, 8);
   it->left_nz_[8] = 0;
 }
 
@@ -38,43 +35,60 @@ static void InitTop(VP8EncIterator* const it) {
   memset(enc->nz_, 0, enc->mb_w_ * sizeof(*enc->nz_));
 }
 
-void VP8IteratorReset(VP8EncIterator* const it) {
+void VP8IteratorSetRow(VP8EncIterator* const it, int y) {
   VP8Encoder* const enc = it->enc_;
   it->x_ = 0;
-  it->y_ = 0;
-  it->y_offset_ = 0;
-  it->uv_offset_ = 0;
-  it->mb_ = enc->mb_info_;
-  it->preds_ = enc->preds_;
+  it->y_ = y;
+  it->bw_ = &enc->parts_[y & (enc->num_parts_ - 1)];
+  it->preds_ = enc->preds_ + y * 4 * enc->preds_w_;
   it->nz_ = enc->nz_;
-  it->bw_ = &enc->parts_[0];
-  it->done_ = enc->mb_w_* enc->mb_h_;
+  it->mb_ = enc->mb_info_ + y * enc->mb_w_;
+  it->y_top_ = enc->y_top_;
+  it->uv_top_ = enc->uv_top_;
+  InitLeft(it);
+}
+
+void VP8IteratorReset(VP8EncIterator* const it) {
+  VP8Encoder* const enc = it->enc_;
+  VP8IteratorSetRow(it, 0);
+  VP8IteratorSetCountDown(it, enc->mb_w_ * enc->mb_h_);  // default
   InitTop(it);
   InitLeft(it);
   memset(it->bit_count_, 0, sizeof(it->bit_count_));
   it->do_trellis_ = 0;
 }
 
+void VP8IteratorSetCountDown(VP8EncIterator* const it, int count_down) {
+  it->count_down_ = it->count_down0_ = count_down;
+}
+
+int VP8IteratorIsDone(const VP8EncIterator* const it) {
+  return (it->count_down_ <= 0);
+}
+
 void VP8IteratorInit(VP8Encoder* const enc, VP8EncIterator* const it) {
   it->enc_ = enc;
   it->y_stride_  = enc->pic_->y_stride;
   it->uv_stride_ = enc->pic_->uv_stride;
-  // TODO(later): for multithreading, these should be owned by 'it'.
-  it->yuv_in_   = enc->yuv_in_;
-  it->yuv_out_  = enc->yuv_out_;
-  it->yuv_out2_ = enc->yuv_out2_;
-  it->yuv_p_    = enc->yuv_p_;
+  it->yuv_in_   = (uint8_t*)WEBP_ALIGN(it->yuv_mem_);
+  it->yuv_out_  = it->yuv_in_ + YUV_SIZE_ENC;
+  it->yuv_out2_ = it->yuv_out_ + YUV_SIZE_ENC;
+  it->yuv_p_    = it->yuv_out2_ + YUV_SIZE_ENC;
   it->lf_stats_ = enc->lf_stats_;
   it->percent0_ = enc->percent_;
+  it->y_left_ = (uint8_t*)WEBP_ALIGN(it->yuv_left_mem_ + 1);
+  it->u_left_ = it->y_left_ + 16 + 16;
+  it->v_left_ = it->u_left_ + 16;
   VP8IteratorReset(it);
 }
 
 int VP8IteratorProgress(const VP8EncIterator* const it, int delta) {
   VP8Encoder* const enc = it->enc_;
-  if (delta && enc->pic_->progress_hook) {
-    const int percent = (enc->mb_h_ <= 1)
+  if (delta && enc->pic_->progress_hook != NULL) {
+    const int done = it->count_down0_ - it->count_down_;
+    const int percent = (it->count_down0_ <= 0)
                       ? it->percent0_
-                      : it->percent0_ + delta * it->y_ / (enc->mb_h_ - 1);
+                      : it->percent0_ + delta * done / it->count_down0_;
     return WebPReportProgress(enc->pic_, percent, &enc->percent_);
   }
   return 1;
@@ -84,6 +98,8 @@ int VP8IteratorProgress(const VP8EncIterator* const it, int delta) {
 // Import the source samples into the cache. Takes care of replicating
 // boundary pixels if necessary.
 
+static WEBP_INLINE int MinSize(int a, int b) { return (a < b) ? a : b; }
+
 static void ImportBlock(const uint8_t* src, int src_stride,
                         uint8_t* dst, int w, int h, int size) {
   int i;
@@ -101,30 +117,55 @@ static void ImportBlock(const uint8_t* src, int src_stride,
   }
 }
 
-void VP8IteratorImport(const VP8EncIterator* const it) {
+static void ImportLine(const uint8_t* src, int src_stride,
+                       uint8_t* dst, int len, int total_len) {
+  int i;
+  for (i = 0; i < len; ++i, src += src_stride) dst[i] = *src;
+  for (; i < total_len; ++i) dst[i] = dst[len - 1];
+}
+
+void VP8IteratorImport(VP8EncIterator* const it, uint8_t* tmp_32) {
   const VP8Encoder* const enc = it->enc_;
   const int x = it->x_, y = it->y_;
   const WebPPicture* const pic = enc->pic_;
-  const uint8_t* const ysrc = pic->y + (y * pic->y_stride + x) * 16;
+  const uint8_t* const ysrc = pic->y + (y * pic->y_stride  + x) * 16;
   const uint8_t* const usrc = pic->u + (y * pic->uv_stride + x) * 8;
   const uint8_t* const vsrc = pic->v + (y * pic->uv_stride + x) * 8;
-  uint8_t* const ydst = it->yuv_in_ + Y_OFF;
-  uint8_t* const udst = it->yuv_in_ + U_OFF;
-  uint8_t* const vdst = it->yuv_in_ + V_OFF;
-  int w = (pic->width - x * 16);
-  int h = (pic->height - y * 16);
-
-  if (w > 16) w = 16;
-  if (h > 16) h = 16;
-
-  // Luma plane
-  ImportBlock(ysrc, pic->y_stride, ydst, w, h, 16);
-
-  {   // U/V planes
-    const int uv_w = (w + 1) >> 1;
-    const int uv_h = (h + 1) >> 1;
-    ImportBlock(usrc, pic->uv_stride, udst, uv_w, uv_h, 8);
-    ImportBlock(vsrc, pic->uv_stride, vdst, uv_w, uv_h, 8);
+  const int w = MinSize(pic->width - x * 16, 16);
+  const int h = MinSize(pic->height - y * 16, 16);
+  const int uv_w = (w + 1) >> 1;
+  const int uv_h = (h + 1) >> 1;
+
+  ImportBlock(ysrc, pic->y_stride,  it->yuv_in_ + Y_OFF_ENC, w, h, 16);
+  ImportBlock(usrc, pic->uv_stride, it->yuv_in_ + U_OFF_ENC, uv_w, uv_h, 8);
+  ImportBlock(vsrc, pic->uv_stride, it->yuv_in_ + V_OFF_ENC, uv_w, uv_h, 8);
+
+  if (tmp_32 == NULL) return;
+
+  // Import source (uncompressed) samples into boundary.
+  if (x == 0) {
+    InitLeft(it);
+  } else {
+    if (y == 0) {
+      it->y_left_[-1] = it->u_left_[-1] = it->v_left_[-1] = 127;
+    } else {
+      it->y_left_[-1] = ysrc[- 1 - pic->y_stride];
+      it->u_left_[-1] = usrc[- 1 - pic->uv_stride];
+      it->v_left_[-1] = vsrc[- 1 - pic->uv_stride];
+    }
+    ImportLine(ysrc - 1, pic->y_stride,  it->y_left_, h,   16);
+    ImportLine(usrc - 1, pic->uv_stride, it->u_left_, uv_h, 8);
+    ImportLine(vsrc - 1, pic->uv_stride, it->v_left_, uv_h, 8);
+  }
+
+  it->y_top_  = tmp_32 + 0;
+  it->uv_top_ = tmp_32 + 16;
+  if (y == 0) {
+    memset(tmp_32, 127, 32 * sizeof(*tmp_32));
+  } else {
+    ImportLine(ysrc - pic->y_stride,  1, tmp_32,          w,   16);
+    ImportLine(usrc - pic->uv_stride, 1, tmp_32 + 16,     uv_w, 8);
+    ImportLine(vsrc - pic->uv_stride, 1, tmp_32 + 16 + 8, uv_w, 8);
   }
 }
 
@@ -144,9 +185,9 @@ void VP8IteratorExport(const VP8EncIterator* const it) {
   const VP8Encoder* const enc = it->enc_;
   if (enc->config_->show_compressed) {
     const int x = it->x_, y = it->y_;
-    const uint8_t* const ysrc = it->yuv_out_ + Y_OFF;
-    const uint8_t* const usrc = it->yuv_out_ + U_OFF;
-    const uint8_t* const vsrc = it->yuv_out_ + V_OFF;
+    const uint8_t* const ysrc = it->yuv_out_ + Y_OFF_ENC;
+    const uint8_t* const usrc = it->yuv_out_ + U_OFF_ENC;
+    const uint8_t* const vsrc = it->yuv_out_ + V_OFF_ENC;
     const WebPPicture* const pic = enc->pic_;
     uint8_t* const ydst = pic->y + (y * pic->y_stride + x) * 16;
     uint8_t* const udst = pic->u + (y * pic->uv_stride + x) * 8;
@@ -240,48 +281,44 @@ void VP8IteratorBytesToNz(VP8EncIterator* const it) {
 #undef BIT
 
 //------------------------------------------------------------------------------
-// Advance to the next position, doing the bookeeping.
+// Advance to the next position, doing the bookkeeping.
 
-int VP8IteratorNext(VP8EncIterator* const it,
-                    const uint8_t* const block_to_save) {
+void VP8IteratorSaveBoundary(VP8EncIterator* const it) {
   VP8Encoder* const enc = it->enc_;
-  if (block_to_save) {
-    const int x = it->x_, y = it->y_;
-    const uint8_t* const ysrc = block_to_save + Y_OFF;
-    const uint8_t* const usrc = block_to_save + U_OFF;
-    if (x < enc->mb_w_ - 1) {   // left
-      int i;
-      for (i = 0; i < 16; ++i) {
-        enc->y_left_[i] = ysrc[15 + i * BPS];
-      }
-      for (i = 0; i < 8; ++i) {
-        enc->u_left_[i] = usrc[7 + i * BPS];
-        enc->v_left_[i] = usrc[15 + i * BPS];
-      }
-      // top-left (before 'top'!)
-      enc->y_left_[-1] = enc->y_top_[x * 16 + 15];
-      enc->u_left_[-1] = enc->uv_top_[x * 16 + 0 + 7];
-      enc->v_left_[-1] = enc->uv_top_[x * 16 + 8 + 7];
+  const int x = it->x_, y = it->y_;
+  const uint8_t* const ysrc = it->yuv_out_ + Y_OFF_ENC;
+  const uint8_t* const uvsrc = it->yuv_out_ + U_OFF_ENC;
+  if (x < enc->mb_w_ - 1) {   // left
+    int i;
+    for (i = 0; i < 16; ++i) {
+      it->y_left_[i] = ysrc[15 + i * BPS];
     }
-    if (y < enc->mb_h_ - 1) {  // top
-      memcpy(enc->y_top_ + x * 16, ysrc + 15 * BPS, 16);
-      memcpy(enc->uv_top_ + x * 16, usrc + 7 * BPS, 8 + 8);
+    for (i = 0; i < 8; ++i) {
+      it->u_left_[i] = uvsrc[7 + i * BPS];
+      it->v_left_[i] = uvsrc[15 + i * BPS];
     }
+    // top-left (before 'top'!)
+    it->y_left_[-1] = it->y_top_[15];
+    it->u_left_[-1] = it->uv_top_[0 + 7];
+    it->v_left_[-1] = it->uv_top_[8 + 7];
   }
+  if (y < enc->mb_h_ - 1) {  // top
+    memcpy(it->y_top_, ysrc + 15 * BPS, 16);
+    memcpy(it->uv_top_, uvsrc + 7 * BPS, 8 + 8);
+  }
+}
 
-  it->mb_++;
+int VP8IteratorNext(VP8EncIterator* const it) {
   it->preds_ += 4;
-  it->nz_++;
-  it->x_++;
-  if (it->x_ == enc->mb_w_) {
-    it->x_ = 0;
-    it->y_++;
-    it->bw_ = &enc->parts_[it->y_ & (enc->num_parts_ - 1)];
-    it->preds_ = enc->preds_ + it->y_ * 4 * enc->preds_w_;
-    it->nz_ = enc->nz_;
-    InitLeft(it);
+  it->mb_ += 1;
+  it->nz_ += 1;
+  it->y_top_ += 16;
+  it->uv_top_ += 16;
+  it->x_ += 1;
+  if (it->x_ == it->enc_->mb_w_) {
+    VP8IteratorSetRow(it, ++it->y_);
   }
-  return (0 < --it->done_);
+  return (0 < --it->count_down_);
 }
 
 //------------------------------------------------------------------------------
@@ -368,15 +405,15 @@ void VP8IteratorStartI4(VP8EncIterator* const it) {
 
   // Import the boundary samples
   for (i = 0; i < 17; ++i) {    // left
-    it->i4_boundary_[i] = enc->y_left_[15 - i];
+    it->i4_boundary_[i] = it->y_left_[15 - i];
   }
   for (i = 0; i < 16; ++i) {    // top
-    it->i4_boundary_[17 + i] = enc->y_top_[it->x_ * 16 + i];
+    it->i4_boundary_[17 + i] = it->y_top_[i];
   }
   // top-right samples have a special case on the far right of the picture
   if (it->x_ < enc->mb_w_ - 1) {
     for (i = 16; i < 16 + 4; ++i) {
-      it->i4_boundary_[17 + i] = enc->y_top_[it->x_ * 16 + i];
+      it->i4_boundary_[17 + i] = it->y_top_[i];
     }
   } else {    // else, replicate the last valid pixel four times
     for (i = 16; i < 16 + 4; ++i) {
@@ -417,6 +454,3 @@ int VP8IteratorRotateI4(VP8EncIterator* const it,
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/layer.c b/drivers/webp/enc/layer.c
deleted file mode 100644
index 423127df63..0000000000
--- a/drivers/webp/enc/layer.c
+++ /dev/null
@@ -1,49 +0,0 @@
-// Copyright 2011 Google Inc. All Rights Reserved.
-//
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
-// -----------------------------------------------------------------------------
-//
-// Enhancement layer (for YUV444/422)
-//
-// Author: Skal (pascal.massimino@gmail.com)
-
-#include <stdlib.h>
-
-#include "./vp8enci.h"
-
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
-//------------------------------------------------------------------------------
-
-void VP8EncInitLayer(VP8Encoder* const enc) {
-  enc->use_layer_ = (enc->pic_->u0 != NULL);
-  enc->layer_data_size_ = 0;
-  enc->layer_data_ = NULL;
-  if (enc->use_layer_) {
-    VP8BitWriterInit(&enc->layer_bw_, enc->mb_w_ * enc->mb_h_ * 3);
-  }
-}
-
-void VP8EncCodeLayerBlock(VP8EncIterator* it) {
-  (void)it;   // remove a warning
-}
-
-int VP8EncFinishLayer(VP8Encoder* const enc) {
-  if (enc->use_layer_) {
-    enc->layer_data_ = VP8BitWriterFinish(&enc->layer_bw_);
-    enc->layer_data_size_ = VP8BitWriterSize(&enc->layer_bw_);
-  }
-  return 1;
-}
-
-void VP8EncDeleteLayer(VP8Encoder* enc) {
-  free(enc->layer_data_);
-}
-
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/picture.c b/drivers/webp/enc/picture.c
index 44eed06083..26679a72e4 100644
--- a/drivers/webp/enc/picture.c
+++ b/drivers/webp/enc/picture.c
@@ -1,470 +1,179 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
-// WebPPicture utils: colorspace conversion, crop, ...
+// WebPPicture class basis
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
 #include <assert.h>
 #include <stdlib.h>
-#include <math.h>
 
 #include "./vp8enci.h"
-#include "../utils/rescaler.h"
-#include "../utils/utils.h"
 #include "../dsp/dsp.h"
-#include "../dsp/yuv.h"
-
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
-#define HALVE(x) (((x) + 1) >> 1)
-#define IS_YUV_CSP(csp, YUV_CSP) (((csp) & WEBP_CSP_UV_MASK) == (YUV_CSP))
-
-static const union {
-  uint32_t argb;
-  uint8_t  bytes[4];
-} test_endian = { 0xff000000u };
-#define ALPHA_IS_LAST (test_endian.bytes[3] == 0xff)
+#include "../utils/utils.h"
 
 //------------------------------------------------------------------------------
 // WebPPicture
 //------------------------------------------------------------------------------
 
-int WebPPictureAlloc(WebPPicture* picture) {
-  if (picture != NULL) {
-    const WebPEncCSP uv_csp = picture->colorspace & WEBP_CSP_UV_MASK;
-    const int has_alpha = picture->colorspace & WEBP_CSP_ALPHA_BIT;
-    const int width = picture->width;
-    const int height = picture->height;
-
-    if (!picture->use_argb) {
-      const int y_stride = width;
-      const int uv_width = HALVE(width);
-      const int uv_height = HALVE(height);
-      const int uv_stride = uv_width;
-      int uv0_stride = 0;
-      int a_width, a_stride;
-      uint64_t y_size, uv_size, uv0_size, a_size, total_size;
-      uint8_t* mem;
-
-      // U/V
-      switch (uv_csp) {
-        case WEBP_YUV420:
-          break;
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-        case WEBP_YUV400:    // for now, we'll just reset the U/V samples
-          break;
-        case WEBP_YUV422:
-          uv0_stride = uv_width;
-          break;
-        case WEBP_YUV444:
-          uv0_stride = width;
-          break;
-#endif
-        default:
-          return 0;
-      }
-      uv0_size = height * uv0_stride;
-
-      // alpha
-      a_width = has_alpha ? width : 0;
-      a_stride = a_width;
-      y_size = (uint64_t)y_stride * height;
-      uv_size = (uint64_t)uv_stride * uv_height;
-      a_size =  (uint64_t)a_stride * height;
-
-      total_size = y_size + a_size + 2 * uv_size + 2 * uv0_size;
-
-      // Security and validation checks
-      if (width <= 0 || height <= 0 ||         // luma/alpha param error
-          uv_width < 0 || uv_height < 0) {     // u/v param error
-        return 0;
-      }
-      // Clear previous buffer and allocate a new one.
-      WebPPictureFree(picture);   // erase previous buffer
-      mem = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*mem));
-      if (mem == NULL) return 0;
-
-      // From now on, we're in the clear, we can no longer fail...
-      picture->memory_ = (void*)mem;
-      picture->y_stride  = y_stride;
-      picture->uv_stride = uv_stride;
-      picture->a_stride  = a_stride;
-      picture->uv0_stride = uv0_stride;
-      // TODO(skal): we could align the y/u/v planes and adjust stride.
-      picture->y = mem;
-      mem += y_size;
-
-      picture->u = mem;
-      mem += uv_size;
-      picture->v = mem;
-      mem += uv_size;
-
-      if (a_size) {
-        picture->a = mem;
-        mem += a_size;
-      }
-      if (uv0_size) {
-        picture->u0 = mem;
-        mem += uv0_size;
-        picture->v0 = mem;
-        mem += uv0_size;
-      }
-    } else {
-      void* memory;
-      const uint64_t argb_size = (uint64_t)width * height;
-      if (width <= 0 || height <= 0) {
-        return 0;
-      }
-      // Clear previous buffer and allocate a new one.
-      WebPPictureFree(picture);   // erase previous buffer
-      memory = WebPSafeMalloc(argb_size, sizeof(*picture->argb));
-      if (memory == NULL) return 0;
+static int DummyWriter(const uint8_t* data, size_t data_size,
+                       const WebPPicture* const picture) {
+  // The following are to prevent 'unused variable' error message.
+  (void)data;
+  (void)data_size;
+  (void)picture;
+  return 1;
+}
 
-      // TODO(skal): align plane to cache line?
-      picture->memory_argb_ = memory;
-      picture->argb = (uint32_t*)memory;
-      picture->argb_stride = width;
-    }
+int WebPPictureInitInternal(WebPPicture* picture, int version) {
+  if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_ENCODER_ABI_VERSION)) {
+    return 0;   // caller/system version mismatch!
+  }
+  if (picture != NULL) {
+    memset(picture, 0, sizeof(*picture));
+    picture->writer = DummyWriter;
+    WebPEncodingSetError(picture, VP8_ENC_OK);
   }
   return 1;
 }
 
-// Remove reference to the ARGB buffer (doesn't free anything).
-static void PictureResetARGB(WebPPicture* const picture) {
+//------------------------------------------------------------------------------
+
+static void WebPPictureResetBufferARGB(WebPPicture* const picture) {
   picture->memory_argb_ = NULL;
   picture->argb = NULL;
   picture->argb_stride = 0;
 }
 
-// Remove reference to the YUVA buffer (doesn't free anything).
-static void PictureResetYUVA(WebPPicture* const picture) {
+static void WebPPictureResetBufferYUVA(WebPPicture* const picture) {
   picture->memory_ = NULL;
   picture->y = picture->u = picture->v = picture->a = NULL;
-  picture->u0 = picture->v0 = NULL;
   picture->y_stride = picture->uv_stride = 0;
   picture->a_stride = 0;
-  picture->uv0_stride = 0;
 }
 
-// Grab the 'specs' (writer, *opaque, width, height...) from 'src' and copy them
-// into 'dst'. Mark 'dst' as not owning any memory.
-static void WebPPictureGrabSpecs(const WebPPicture* const src,
-                                 WebPPicture* const dst) {
-  assert(src != NULL && dst != NULL);
-  *dst = *src;
-  PictureResetYUVA(dst);
-  PictureResetARGB(dst);
+void WebPPictureResetBuffers(WebPPicture* const picture) {
+  WebPPictureResetBufferARGB(picture);
+  WebPPictureResetBufferYUVA(picture);
 }
 
-// Allocate a new argb buffer, discarding any existing one and preserving
-// the other YUV(A) buffer.
-static int PictureAllocARGB(WebPPicture* const picture) {
-  WebPPicture tmp;
-  free(picture->memory_argb_);
-  PictureResetARGB(picture);
-  picture->use_argb = 1;
-  WebPPictureGrabSpecs(picture, &tmp);
-  if (!WebPPictureAlloc(&tmp)) {
-    return WebPEncodingSetError(picture, VP8_ENC_ERROR_OUT_OF_MEMORY);
-  }
-  picture->memory_argb_ = tmp.memory_argb_;
-  picture->argb = tmp.argb;
-  picture->argb_stride = tmp.argb_stride;
-  return 1;
-}
+int WebPPictureAllocARGB(WebPPicture* const picture, int width, int height) {
+  void* memory;
+  const uint64_t argb_size = (uint64_t)width * height;
 
-// Release memory owned by 'picture' (both YUV and ARGB buffers).
-void WebPPictureFree(WebPPicture* picture) {
-  if (picture != NULL) {
-    free(picture->memory_);
-    free(picture->memory_argb_);
-    PictureResetYUVA(picture);
-    PictureResetARGB(picture);
-  }
-}
+  assert(picture != NULL);
 
-//------------------------------------------------------------------------------
-// Picture copying
+  WebPSafeFree(picture->memory_argb_);
+  WebPPictureResetBufferARGB(picture);
 
-// Not worth moving to dsp/enc.c (only used here).
-static void CopyPlane(const uint8_t* src, int src_stride,
-                      uint8_t* dst, int dst_stride, int width, int height) {
-  while (height-- > 0) {
-    memcpy(dst, src, width);
-    src += src_stride;
-    dst += dst_stride;
+  if (width <= 0 || height <= 0) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_BAD_DIMENSION);
   }
-}
-
-// Adjust top-left corner to chroma sample position.
-static void SnapTopLeftPosition(const WebPPicture* const pic,
-                                int* const left, int* const top) {
-  if (!pic->use_argb) {
-    const int is_yuv422 = IS_YUV_CSP(pic->colorspace, WEBP_YUV422);
-    if (IS_YUV_CSP(pic->colorspace, WEBP_YUV420) || is_yuv422) {
-      *left &= ~1;
-      if (!is_yuv422) *top &= ~1;
-    }
+  // allocate a new buffer.
+  memory = WebPSafeMalloc(argb_size, sizeof(*picture->argb));
+  if (memory == NULL) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_OUT_OF_MEMORY);
   }
-}
-
-// Adjust top-left corner and verify that the sub-rectangle is valid.
-static int AdjustAndCheckRectangle(const WebPPicture* const pic,
-                                   int* const left, int* const top,
-                                   int width, int height) {
-  SnapTopLeftPosition(pic, left, top);
-  if ((*left) < 0 || (*top) < 0) return 0;
-  if (width <= 0 || height <= 0) return 0;
-  if ((*left) + width > pic->width) return 0;
-  if ((*top) + height > pic->height) return 0;
+  // TODO(skal): align plane to cache line?
+  picture->memory_argb_ = memory;
+  picture->argb = (uint32_t*)memory;
+  picture->argb_stride = width;
   return 1;
 }
 
-int WebPPictureCopy(const WebPPicture* src, WebPPicture* dst) {
-  if (src == NULL || dst == NULL) return 0;
-  if (src == dst) return 1;
+int WebPPictureAllocYUVA(WebPPicture* const picture, int width, int height) {
+  const WebPEncCSP uv_csp = picture->colorspace & WEBP_CSP_UV_MASK;
+  const int has_alpha = picture->colorspace & WEBP_CSP_ALPHA_BIT;
+  const int y_stride = width;
+  const int uv_width = (width + 1) >> 1;
+  const int uv_height = (height + 1) >> 1;
+  const int uv_stride = uv_width;
+  int a_width, a_stride;
+  uint64_t y_size, uv_size, a_size, total_size;
+  uint8_t* mem;
 
-  WebPPictureGrabSpecs(src, dst);
-  if (!WebPPictureAlloc(dst)) return 0;
+  assert(picture != NULL);
 
-  if (!src->use_argb) {
-    CopyPlane(src->y, src->y_stride,
-              dst->y, dst->y_stride, dst->width, dst->height);
-    CopyPlane(src->u, src->uv_stride,
-              dst->u, dst->uv_stride, HALVE(dst->width), HALVE(dst->height));
-    CopyPlane(src->v, src->uv_stride,
-              dst->v, dst->uv_stride, HALVE(dst->width), HALVE(dst->height));
-    if (dst->a != NULL)  {
-      CopyPlane(src->a, src->a_stride,
-                dst->a, dst->a_stride, dst->width, dst->height);
-    }
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    if (dst->u0 != NULL)  {
-      int uv0_width = src->width;
-      if (IS_YUV_CSP(dst->colorspace, WEBP_YUV422)) {
-        uv0_width = HALVE(uv0_width);
-      }
-      CopyPlane(src->u0, src->uv0_stride,
-                dst->u0, dst->uv0_stride, uv0_width, dst->height);
-      CopyPlane(src->v0, src->uv0_stride,
-                dst->v0, dst->uv0_stride, uv0_width, dst->height);
-    }
-#endif
-  } else {
-    CopyPlane((const uint8_t*)src->argb, 4 * src->argb_stride,
-              (uint8_t*)dst->argb, 4 * dst->argb_stride,
-              4 * dst->width, dst->height);
-  }
-  return 1;
-}
+  WebPSafeFree(picture->memory_);
+  WebPPictureResetBufferYUVA(picture);
 
-int WebPPictureIsView(const WebPPicture* picture) {
-  if (picture == NULL) return 0;
-  if (picture->use_argb) {
-    return (picture->memory_argb_ == NULL);
+  if (uv_csp != WEBP_YUV420) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_INVALID_CONFIGURATION);
   }
-  return (picture->memory_ == NULL);
-}
 
-int WebPPictureView(const WebPPicture* src,
-                    int left, int top, int width, int height,
-                    WebPPicture* dst) {
-  if (src == NULL || dst == NULL) return 0;
+  // alpha
+  a_width = has_alpha ? width : 0;
+  a_stride = a_width;
+  y_size = (uint64_t)y_stride * height;
+  uv_size = (uint64_t)uv_stride * uv_height;
+  a_size =  (uint64_t)a_stride * height;
 
-  // verify rectangle position.
-  if (!AdjustAndCheckRectangle(src, &left, &top, width, height)) return 0;
+  total_size = y_size + a_size + 2 * uv_size;
 
-  if (src != dst) {  // beware of aliasing! We don't want to leak 'memory_'.
-    WebPPictureGrabSpecs(src, dst);
+  // Security and validation checks
+  if (width <= 0 || height <= 0 ||         // luma/alpha param error
+      uv_width < 0 || uv_height < 0) {     // u/v param error
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_BAD_DIMENSION);
   }
-  dst->width = width;
-  dst->height = height;
-  if (!src->use_argb) {
-    dst->y = src->y + top * src->y_stride + left;
-    dst->u = src->u + (top >> 1) * src->uv_stride + (left >> 1);
-    dst->v = src->v + (top >> 1) * src->uv_stride + (left >> 1);
-    if (src->a != NULL) {
-      dst->a = src->a + top * src->a_stride + left;
-    }
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    if (src->u0 != NULL) {
-      const int left_pos =
-          IS_YUV_CSP(dst->colorspace, WEBP_YUV422) ? (left >> 1) : left;
-      dst->u0 = src->u0 + top * src->uv0_stride + left_pos;
-      dst->v0 = src->v0 + top * src->uv0_stride + left_pos;
-    }
-#endif
-  } else {
-    dst->argb = src->argb + top * src->argb_stride + left;
+  // allocate a new buffer.
+  mem = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*mem));
+  if (mem == NULL) {
+    return WebPEncodingSetError(picture, VP8_ENC_ERROR_OUT_OF_MEMORY);
   }
-  return 1;
-}
 
-//------------------------------------------------------------------------------
-// Picture cropping
+  // From now on, we're in the clear, we can no longer fail...
+  picture->memory_ = (void*)mem;
+  picture->y_stride  = y_stride;
+  picture->uv_stride = uv_stride;
+  picture->a_stride  = a_stride;
 
-int WebPPictureCrop(WebPPicture* pic,
-                    int left, int top, int width, int height) {
-  WebPPicture tmp;
+  // TODO(skal): we could align the y/u/v planes and adjust stride.
+  picture->y = mem;
+  mem += y_size;
 
-  if (pic == NULL) return 0;
-  if (!AdjustAndCheckRectangle(pic, &left, &top, width, height)) return 0;
+  picture->u = mem;
+  mem += uv_size;
+  picture->v = mem;
+  mem += uv_size;
 
-  WebPPictureGrabSpecs(pic, &tmp);
-  tmp.width = width;
-  tmp.height = height;
-  if (!WebPPictureAlloc(&tmp)) return 0;
-
-  if (!pic->use_argb) {
-    const int y_offset = top * pic->y_stride + left;
-    const int uv_offset = (top / 2) * pic->uv_stride + left / 2;
-    CopyPlane(pic->y + y_offset, pic->y_stride,
-              tmp.y, tmp.y_stride, width, height);
-    CopyPlane(pic->u + uv_offset, pic->uv_stride,
-              tmp.u, tmp.uv_stride, HALVE(width), HALVE(height));
-    CopyPlane(pic->v + uv_offset, pic->uv_stride,
-              tmp.v, tmp.uv_stride, HALVE(width), HALVE(height));
-
-    if (tmp.a != NULL) {
-      const int a_offset = top * pic->a_stride + left;
-      CopyPlane(pic->a + a_offset, pic->a_stride,
-                tmp.a, tmp.a_stride, width, height);
-    }
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    if (tmp.u0 != NULL) {
-      int w = width;
-      int left_pos = left;
-      if (IS_YUV_CSP(tmp.colorspace, WEBP_YUV422)) {
-        w = HALVE(w);
-        left_pos = HALVE(left_pos);
-      }
-      CopyPlane(pic->u0 + top * pic->uv0_stride + left_pos, pic->uv0_stride,
-                tmp.u0, tmp.uv0_stride, w, height);
-      CopyPlane(pic->v0 + top * pic->uv0_stride + left_pos, pic->uv0_stride,
-                tmp.v0, tmp.uv0_stride, w, height);
-    }
-#endif
-  } else {
-    const uint8_t* const src =
-        (const uint8_t*)(pic->argb + top * pic->argb_stride + left);
-    CopyPlane(src, pic->argb_stride * 4,
-              (uint8_t*)tmp.argb, tmp.argb_stride * 4,
-              width * 4, height);
+  if (a_size > 0) {
+    picture->a = mem;
+    mem += a_size;
   }
-  WebPPictureFree(pic);
-  *pic = tmp;
+  (void)mem;  // makes the static analyzer happy
   return 1;
 }
 
-//------------------------------------------------------------------------------
-// Simple picture rescaler
-
-static void RescalePlane(const uint8_t* src,
-                         int src_width, int src_height, int src_stride,
-                         uint8_t* dst,
-                         int dst_width, int dst_height, int dst_stride,
-                         int32_t* const work,
-                         int num_channels) {
-  WebPRescaler rescaler;
-  int y = 0;
-  WebPRescalerInit(&rescaler, src_width, src_height,
-                   dst, dst_width, dst_height, dst_stride,
-                   num_channels,
-                   src_width, dst_width,
-                   src_height, dst_height,
-                   work);
-  memset(work, 0, 2 * dst_width * num_channels * sizeof(*work));
-  while (y < src_height) {
-    y += WebPRescalerImport(&rescaler, src_height - y,
-                            src + y * src_stride, src_stride);
-    WebPRescalerExport(&rescaler);
-  }
-}
-
-int WebPPictureRescale(WebPPicture* pic, int width, int height) {
-  WebPPicture tmp;
-  int prev_width, prev_height;
-  int32_t* work;
-
-  if (pic == NULL) return 0;
-  prev_width = pic->width;
-  prev_height = pic->height;
-  // if width is unspecified, scale original proportionally to height ratio.
-  if (width == 0) {
-    width = (prev_width * height + prev_height / 2) / prev_height;
-  }
-  // if height is unspecified, scale original proportionally to width ratio.
-  if (height == 0) {
-    height = (prev_height * width + prev_width / 2) / prev_width;
-  }
-  // Check if the overall dimensions still make sense.
-  if (width <= 0 || height <= 0) return 0;
-
-  WebPPictureGrabSpecs(pic, &tmp);
-  tmp.width = width;
-  tmp.height = height;
-  if (!WebPPictureAlloc(&tmp)) return 0;
-
-  if (!pic->use_argb) {
-    work = (int32_t*)WebPSafeMalloc(2ULL * width, sizeof(*work));
-    if (work == NULL) {
-      WebPPictureFree(&tmp);
-      return 0;
-    }
+int WebPPictureAlloc(WebPPicture* picture) {
+  if (picture != NULL) {
+    const int width = picture->width;
+    const int height = picture->height;
 
-    RescalePlane(pic->y, prev_width, prev_height, pic->y_stride,
-                 tmp.y, width, height, tmp.y_stride, work, 1);
-    RescalePlane(pic->u,
-                 HALVE(prev_width), HALVE(prev_height), pic->uv_stride,
-                 tmp.u,
-                 HALVE(width), HALVE(height), tmp.uv_stride, work, 1);
-    RescalePlane(pic->v,
-                 HALVE(prev_width), HALVE(prev_height), pic->uv_stride,
-                 tmp.v,
-                 HALVE(width), HALVE(height), tmp.uv_stride, work, 1);
+    WebPPictureFree(picture);   // erase previous buffer
 
-    if (tmp.a != NULL) {
-      RescalePlane(pic->a, prev_width, prev_height, pic->a_stride,
-                   tmp.a, width, height, tmp.a_stride, work, 1);
-    }
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    if (tmp.u0 != NULL) {
-      const int s = IS_YUV_CSP(tmp.colorspace, WEBP_YUV422) ? 2 : 1;
-      RescalePlane(
-          pic->u0, (prev_width + s / 2) / s, prev_height, pic->uv0_stride,
-          tmp.u0, (width + s / 2) / s, height, tmp.uv0_stride, work, 1);
-      RescalePlane(
-          pic->v0, (prev_width + s / 2) / s, prev_height, pic->uv0_stride,
-          tmp.v0, (width + s / 2) / s, height, tmp.uv0_stride, work, 1);
-    }
-#endif
-  } else {
-    work = (int32_t*)WebPSafeMalloc(2ULL * width * 4, sizeof(*work));
-    if (work == NULL) {
-      WebPPictureFree(&tmp);
-      return 0;
+    if (!picture->use_argb) {
+      return WebPPictureAllocYUVA(picture, width, height);
+    } else {
+      return WebPPictureAllocARGB(picture, width, height);
     }
-
-    RescalePlane((const uint8_t*)pic->argb, prev_width, prev_height,
-                 pic->argb_stride * 4,
-                 (uint8_t*)tmp.argb, width, height,
-                 tmp.argb_stride * 4,
-                 work, 4);
-
   }
-  WebPPictureFree(pic);
-  free(work);
-  *pic = tmp;
   return 1;
 }
 
+void WebPPictureFree(WebPPicture* picture) {
+  if (picture != NULL) {
+    WebPSafeFree(picture->memory_);
+    WebPSafeFree(picture->memory_argb_);
+    WebPPictureResetBuffers(picture);
+  }
+}
+
 //------------------------------------------------------------------------------
 // WebPMemoryWriter: Write-to-memory
 
@@ -494,7 +203,7 @@ int WebPMemoryWrite(const uint8_t* data, size_t data_size,
     if (w->size > 0) {
       memcpy(new_mem, w->mem, w->size);
     }
-    free(w->mem);
+    WebPSafeFree(w->mem);
     w->mem = new_mem;
     // down-cast is ok, thanks to WebPSafeMalloc
     w->max_size = (size_t)next_max_size;
@@ -506,469 +215,13 @@ int WebPMemoryWrite(const uint8_t* data, size_t data_size,
   return 1;
 }
 
-//------------------------------------------------------------------------------
-// Detection of non-trivial transparency
-
-// Returns true if alpha[] has non-0xff values.
-static int CheckNonOpaque(const uint8_t* alpha, int width, int height,
-                          int x_step, int y_step) {
-  if (alpha == NULL) return 0;
-  while (height-- > 0) {
-    int x;
-    for (x = 0; x < width * x_step; x += x_step) {
-      if (alpha[x] != 0xff) return 1;  // TODO(skal): check 4/8 bytes at a time.
-    }
-    alpha += y_step;
-  }
-  return 0;
-}
-
-// Checking for the presence of non-opaque alpha.
-int WebPPictureHasTransparency(const WebPPicture* picture) {
-  if (picture == NULL) return 0;
-  if (!picture->use_argb) {
-    return CheckNonOpaque(picture->a, picture->width, picture->height,
-                          1, picture->a_stride);
-  } else {
-    int x, y;
-    const uint32_t* argb = picture->argb;
-    if (argb == NULL) return 0;
-    for (y = 0; y < picture->height; ++y) {
-      for (x = 0; x < picture->width; ++x) {
-        if (argb[x] < 0xff000000u) return 1;   // test any alpha values != 0xff
-      }
-      argb += picture->argb_stride;
-    }
-  }
-  return 0;
-}
-
-//------------------------------------------------------------------------------
-// RGB -> YUV conversion
-
-// TODO: we can do better than simply 2x2 averaging on U/V samples.
-#define SUM4(ptr) ((ptr)[0] + (ptr)[step] + \
-                   (ptr)[rgb_stride] + (ptr)[rgb_stride + step])
-#define SUM2H(ptr) (2 * (ptr)[0] + 2 * (ptr)[step])
-#define SUM2V(ptr) (2 * (ptr)[0] + 2 * (ptr)[rgb_stride])
-#define SUM1(ptr)  (4 * (ptr)[0])
-#define RGB_TO_UV(x, y, SUM) {                           \
-  const int src = (2 * (step * (x) + (y) * rgb_stride)); \
-  const int dst = (x) + (y) * picture->uv_stride;        \
-  const int r = SUM(r_ptr + src);                        \
-  const int g = SUM(g_ptr + src);                        \
-  const int b = SUM(b_ptr + src);                        \
-  picture->u[dst] = VP8RGBToU(r, g, b);                  \
-  picture->v[dst] = VP8RGBToV(r, g, b);                  \
-}
-
-#define RGB_TO_UV0(x_in, x_out, y, SUM) {                \
-  const int src = (step * (x_in) + (y) * rgb_stride);    \
-  const int dst = (x_out) + (y) * picture->uv0_stride;   \
-  const int r = SUM(r_ptr + src);                        \
-  const int g = SUM(g_ptr + src);                        \
-  const int b = SUM(b_ptr + src);                        \
-  picture->u0[dst] = VP8RGBToU(r, g, b);                 \
-  picture->v0[dst] = VP8RGBToV(r, g, b);                 \
-}
-
-static void MakeGray(WebPPicture* const picture) {
-  int y;
-  const int uv_width = HALVE(picture->width);
-  const int uv_height = HALVE(picture->height);
-  for (y = 0; y < uv_height; ++y) {
-    memset(picture->u + y * picture->uv_stride, 128, uv_width);
-    memset(picture->v + y * picture->uv_stride, 128, uv_width);
-  }
-}
-
-static int ImportYUVAFromRGBA(const uint8_t* const r_ptr,
-                              const uint8_t* const g_ptr,
-                              const uint8_t* const b_ptr,
-                              const uint8_t* const a_ptr,
-                              int step,         // bytes per pixel
-                              int rgb_stride,   // bytes per scanline
-                              WebPPicture* const picture) {
-  const WebPEncCSP uv_csp = picture->colorspace & WEBP_CSP_UV_MASK;
-  int x, y;
-  const int width = picture->width;
-  const int height = picture->height;
-  const int has_alpha = CheckNonOpaque(a_ptr, width, height, step, rgb_stride);
-
-  picture->colorspace = uv_csp;
-  picture->use_argb = 0;
-  if (has_alpha) {
-    picture->colorspace |= WEBP_CSP_ALPHA_BIT;
-  }
-  if (!WebPPictureAlloc(picture)) return 0;
-
-  // Import luma plane
-  for (y = 0; y < height; ++y) {
-    for (x = 0; x < width; ++x) {
-      const int offset = step * x + y * rgb_stride;
-      picture->y[x + y * picture->y_stride] =
-          VP8RGBToY(r_ptr[offset], g_ptr[offset], b_ptr[offset]);
-    }
-  }
-
-  // Downsample U/V plane
-  if (uv_csp != WEBP_YUV400) {
-    for (y = 0; y < (height >> 1); ++y) {
-      for (x = 0; x < (width >> 1); ++x) {
-        RGB_TO_UV(x, y, SUM4);
-      }
-      if (width & 1) {
-        RGB_TO_UV(x, y, SUM2V);
-      }
-    }
-    if (height & 1) {
-      for (x = 0; x < (width >> 1); ++x) {
-        RGB_TO_UV(x, y, SUM2H);
-      }
-      if (width & 1) {
-        RGB_TO_UV(x, y, SUM1);
-      }
-    }
-
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    // Store original U/V samples too
-    if (uv_csp == WEBP_YUV422) {
-      for (y = 0; y < height; ++y) {
-        for (x = 0; x < (width >> 1); ++x) {
-          RGB_TO_UV0(2 * x, x, y, SUM2H);
-        }
-        if (width & 1) {
-          RGB_TO_UV0(2 * x, x, y, SUM1);
-        }
-      }
-    } else if (uv_csp == WEBP_YUV444) {
-      for (y = 0; y < height; ++y) {
-        for (x = 0; x < width; ++x) {
-          RGB_TO_UV0(x, x, y, SUM1);
-        }
-      }
-    }
-#endif
-  } else {
-    MakeGray(picture);
-  }
-
-  if (has_alpha) {
-    assert(step >= 4);
-    for (y = 0; y < height; ++y) {
-      for (x = 0; x < width; ++x) {
-        picture->a[x + y * picture->a_stride] =
-            a_ptr[step * x + y * rgb_stride];
-      }
-    }
-  }
-  return 1;
-}
-
-static int Import(WebPPicture* const picture,
-                  const uint8_t* const rgb, int rgb_stride,
-                  int step, int swap_rb, int import_alpha) {
-  const uint8_t* const r_ptr = rgb + (swap_rb ? 2 : 0);
-  const uint8_t* const g_ptr = rgb + 1;
-  const uint8_t* const b_ptr = rgb + (swap_rb ? 0 : 2);
-  const uint8_t* const a_ptr = import_alpha ? rgb + 3 : NULL;
-  const int width = picture->width;
-  const int height = picture->height;
-
-  if (!picture->use_argb) {
-    return ImportYUVAFromRGBA(r_ptr, g_ptr, b_ptr, a_ptr, step, rgb_stride,
-                              picture);
-  }
-  if (import_alpha) {
-    picture->colorspace |= WEBP_CSP_ALPHA_BIT;
-  } else {
-    picture->colorspace &= ~WEBP_CSP_ALPHA_BIT;
-  }
-  if (!WebPPictureAlloc(picture)) return 0;
-
-  if (!import_alpha) {
-    int x, y;
-    for (y = 0; y < height; ++y) {
-      for (x = 0; x < width; ++x) {
-        const int offset = step * x + y * rgb_stride;
-        const uint32_t argb =
-            0xff000000u |
-            (r_ptr[offset] << 16) |
-            (g_ptr[offset] <<  8) |
-            (b_ptr[offset]);
-        picture->argb[x + y * picture->argb_stride] = argb;
-      }
-    }
-  } else {
-    int x, y;
-    assert(step >= 4);
-    for (y = 0; y < height; ++y) {
-      for (x = 0; x < width; ++x) {
-        const int offset = step * x + y * rgb_stride;
-        const uint32_t argb = (a_ptr[offset] << 24) |
-                              (r_ptr[offset] << 16) |
-                              (g_ptr[offset] <<  8) |
-                              (b_ptr[offset]);
-        picture->argb[x + y * picture->argb_stride] = argb;
-      }
-    }
-  }
-  return 1;
-}
-#undef SUM4
-#undef SUM2V
-#undef SUM2H
-#undef SUM1
-#undef RGB_TO_UV
-
-int WebPPictureImportRGB(WebPPicture* picture,
-                         const uint8_t* rgb, int rgb_stride) {
-  return Import(picture, rgb, rgb_stride, 3, 0, 0);
-}
-
-int WebPPictureImportBGR(WebPPicture* picture,
-                         const uint8_t* rgb, int rgb_stride) {
-  return Import(picture, rgb, rgb_stride, 3, 1, 0);
-}
-
-int WebPPictureImportRGBA(WebPPicture* picture,
-                          const uint8_t* rgba, int rgba_stride) {
-  return Import(picture, rgba, rgba_stride, 4, 0, 1);
-}
-
-int WebPPictureImportBGRA(WebPPicture* picture,
-                          const uint8_t* rgba, int rgba_stride) {
-  return Import(picture, rgba, rgba_stride, 4, 1, 1);
-}
-
-int WebPPictureImportRGBX(WebPPicture* picture,
-                          const uint8_t* rgba, int rgba_stride) {
-  return Import(picture, rgba, rgba_stride, 4, 0, 0);
-}
-
-int WebPPictureImportBGRX(WebPPicture* picture,
-                          const uint8_t* rgba, int rgba_stride) {
-  return Import(picture, rgba, rgba_stride, 4, 1, 0);
-}
-
-//------------------------------------------------------------------------------
-// Automatic YUV <-> ARGB conversions.
-
-int WebPPictureYUVAToARGB(WebPPicture* picture) {
-  if (picture == NULL) return 0;
-  if (picture->memory_ == NULL || picture->y == NULL ||
-      picture->u == NULL || picture->v == NULL) {
-    return WebPEncodingSetError(picture, VP8_ENC_ERROR_NULL_PARAMETER);
-  }
-  if ((picture->colorspace & WEBP_CSP_ALPHA_BIT) && picture->a == NULL) {
-    return WebPEncodingSetError(picture, VP8_ENC_ERROR_NULL_PARAMETER);
-  }
-  if ((picture->colorspace & WEBP_CSP_UV_MASK) != WEBP_YUV420) {
-    return WebPEncodingSetError(picture, VP8_ENC_ERROR_INVALID_CONFIGURATION);
-  }
-  // Allocate a new argb buffer (discarding the previous one).
-  if (!PictureAllocARGB(picture)) return 0;
-
-  // Convert
-  {
-    int y;
-    const int width = picture->width;
-    const int height = picture->height;
-    const int argb_stride = 4 * picture->argb_stride;
-    uint8_t* dst = (uint8_t*)picture->argb;
-    const uint8_t *cur_u = picture->u, *cur_v = picture->v, *cur_y = picture->y;
-    WebPUpsampleLinePairFunc upsample = WebPGetLinePairConverter(ALPHA_IS_LAST);
-
-    // First row, with replicated top samples.
-    upsample(NULL, cur_y, cur_u, cur_v, cur_u, cur_v, NULL, dst, width);
-    cur_y += picture->y_stride;
-    dst += argb_stride;
-    // Center rows.
-    for (y = 1; y + 1 < height; y += 2) {
-      const uint8_t* const top_u = cur_u;
-      const uint8_t* const top_v = cur_v;
-      cur_u += picture->uv_stride;
-      cur_v += picture->uv_stride;
-      upsample(cur_y, cur_y + picture->y_stride, top_u, top_v, cur_u, cur_v,
-               dst, dst + argb_stride, width);
-      cur_y += 2 * picture->y_stride;
-      dst += 2 * argb_stride;
-    }
-    // Last row (if needed), with replicated bottom samples.
-    if (height > 1 && !(height & 1)) {
-      upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v, dst, NULL, width);
-    }
-    // Insert alpha values if needed, in replacement for the default 0xff ones.
-    if (picture->colorspace & WEBP_CSP_ALPHA_BIT) {
-      for (y = 0; y < height; ++y) {
-        uint32_t* const dst = picture->argb + y * picture->argb_stride;
-        const uint8_t* const src = picture->a + y * picture->a_stride;
-        int x;
-        for (x = 0; x < width; ++x) {
-          dst[x] = (dst[x] & 0x00ffffffu) | (src[x] << 24);
-        }
-      }
-    }
-  }
-  return 1;
-}
-
-int WebPPictureARGBToYUVA(WebPPicture* picture, WebPEncCSP colorspace) {
-  if (picture == NULL) return 0;
-  if (picture->argb == NULL) {
-    return WebPEncodingSetError(picture, VP8_ENC_ERROR_NULL_PARAMETER);
-  } else {
-    const uint8_t* const argb = (const uint8_t*)picture->argb;
-    const uint8_t* const r = ALPHA_IS_LAST ? argb + 2 : argb + 1;
-    const uint8_t* const g = ALPHA_IS_LAST ? argb + 1 : argb + 2;
-    const uint8_t* const b = ALPHA_IS_LAST ? argb + 0 : argb + 3;
-    const uint8_t* const a = ALPHA_IS_LAST ? argb + 3 : argb + 0;
-    // We work on a tmp copy of 'picture', because ImportYUVAFromRGBA()
-    // would be calling WebPPictureFree(picture) otherwise.
-    WebPPicture tmp = *picture;
-    PictureResetARGB(&tmp);  // reset ARGB buffer so that it's not free()'d.
-    tmp.use_argb = 0;
-    tmp.colorspace = colorspace & WEBP_CSP_UV_MASK;
-    if (!ImportYUVAFromRGBA(r, g, b, a, 4, 4 * picture->argb_stride, &tmp)) {
-      return WebPEncodingSetError(picture, VP8_ENC_ERROR_OUT_OF_MEMORY);
-    }
-    // Copy back the YUV specs into 'picture'.
-    tmp.argb = picture->argb;
-    tmp.argb_stride = picture->argb_stride;
-    tmp.memory_argb_ = picture->memory_argb_;
-    *picture = tmp;
+void WebPMemoryWriterClear(WebPMemoryWriter* writer) {
+  if (writer != NULL) {
+    WebPSafeFree(writer->mem);
+    writer->mem = NULL;
+    writer->size = 0;
+    writer->max_size = 0;
   }
-  return 1;
-}
-
-//------------------------------------------------------------------------------
-// Helper: clean up fully transparent area to help compressibility.
-
-#define SIZE 8
-#define SIZE2 (SIZE / 2)
-static int is_transparent_area(const uint8_t* ptr, int stride, int size) {
-  int y, x;
-  for (y = 0; y < size; ++y) {
-    for (x = 0; x < size; ++x) {
-      if (ptr[x]) {
-        return 0;
-      }
-    }
-    ptr += stride;
-  }
-  return 1;
-}
-
-static WEBP_INLINE void flatten(uint8_t* ptr, int v, int stride, int size) {
-  int y;
-  for (y = 0; y < size; ++y) {
-    memset(ptr, v, size);
-    ptr += stride;
-  }
-}
-
-void WebPCleanupTransparentArea(WebPPicture* pic) {
-  int x, y, w, h;
-  const uint8_t* a_ptr;
-  int values[3] = { 0 };
-
-  if (pic == NULL) return;
-
-  a_ptr = pic->a;
-  if (a_ptr == NULL) return;    // nothing to do
-
-  w = pic->width / SIZE;
-  h = pic->height / SIZE;
-  for (y = 0; y < h; ++y) {
-    int need_reset = 1;
-    for (x = 0; x < w; ++x) {
-      const int off_a = (y * pic->a_stride + x) * SIZE;
-      const int off_y = (y * pic->y_stride + x) * SIZE;
-      const int off_uv = (y * pic->uv_stride + x) * SIZE2;
-      if (is_transparent_area(a_ptr + off_a, pic->a_stride, SIZE)) {
-        if (need_reset) {
-          values[0] = pic->y[off_y];
-          values[1] = pic->u[off_uv];
-          values[2] = pic->v[off_uv];
-          need_reset = 0;
-        }
-        flatten(pic->y + off_y, values[0], pic->y_stride, SIZE);
-        flatten(pic->u + off_uv, values[1], pic->uv_stride, SIZE2);
-        flatten(pic->v + off_uv, values[2], pic->uv_stride, SIZE2);
-      } else {
-        need_reset = 1;
-      }
-    }
-    // ignore the left-overs on right/bottom
-  }
-}
-
-#undef SIZE
-#undef SIZE2
-
-
-//------------------------------------------------------------------------------
-// Distortion
-
-// Max value returned in case of exact similarity.
-static const double kMinDistortion_dB = 99.;
-
-int WebPPictureDistortion(const WebPPicture* pic1, const WebPPicture* pic2,
-                          int type, float result[5]) {
-  int c;
-  DistoStats stats[5];
-  int has_alpha;
-
-  if (pic1 == NULL || pic2 == NULL ||
-      pic1->width != pic2->width || pic1->height != pic2->height ||
-      pic1->y == NULL || pic2->y == NULL ||
-      pic1->u == NULL || pic2->u == NULL ||
-      pic1->v == NULL || pic2->v == NULL ||
-      result == NULL) {
-    return 0;
-  }
-  // TODO(skal): provide distortion for ARGB too.
-  if (pic1->use_argb == 1 || pic1->use_argb != pic2->use_argb) {
-    return 0;
-  }
-
-  has_alpha = !!(pic1->colorspace & WEBP_CSP_ALPHA_BIT);
-  if (has_alpha != !!(pic2->colorspace & WEBP_CSP_ALPHA_BIT) ||
-      (has_alpha && (pic1->a == NULL || pic2->a == NULL))) {
-    return 0;
-  }
-
-  memset(stats, 0, sizeof(stats));
-  VP8SSIMAccumulatePlane(pic1->y, pic1->y_stride,
-                         pic2->y, pic2->y_stride,
-                         pic1->width, pic1->height, &stats[0]);
-  VP8SSIMAccumulatePlane(pic1->u, pic1->uv_stride,
-                         pic2->u, pic2->uv_stride,
-                         (pic1->width + 1) >> 1, (pic1->height + 1) >> 1,
-                         &stats[1]);
-  VP8SSIMAccumulatePlane(pic1->v, pic1->uv_stride,
-                         pic2->v, pic2->uv_stride,
-                         (pic1->width + 1) >> 1, (pic1->height + 1) >> 1,
-                         &stats[2]);
-  if (has_alpha) {
-    VP8SSIMAccumulatePlane(pic1->a, pic1->a_stride,
-                           pic2->a, pic2->a_stride,
-                           pic1->width, pic1->height, &stats[3]);
-  }
-  for (c = 0; c <= 4; ++c) {
-    if (type == 1) {
-      const double v = VP8SSIMGet(&stats[c]);
-      result[c] = (float)((v < 1.) ? -10.0 * log10(1. - v)
-                                   : kMinDistortion_dB);
-    } else {
-      const double v = VP8SSIMGetSquaredError(&stats[c]);
-      result[c] = (float)((v > 0.) ? -4.3429448 * log(v / (255 * 255.))
-                                   : kMinDistortion_dB);
-    }
-    // Accumulate forward
-    if (c < 4) VP8SSIMAddStats(&stats[c], &stats[4]);
-  }
-  return 1;
 }
 
 //------------------------------------------------------------------------------
@@ -1000,7 +253,7 @@ static size_t Encode(const uint8_t* rgba, int width, int height, int stride,
   ok = import(&pic, rgba, stride) && WebPEncode(&config, &pic);
   WebPPictureFree(&pic);
   if (!ok) {
-    free(wrt.mem);
+    WebPMemoryWriterClear(&wrt);
     *output = NULL;
     return 0;
   }
@@ -1014,10 +267,10 @@ size_t NAME(const uint8_t* in, int w, int h, int bps, float q,          \
   return Encode(in, w, h, bps, IMPORTER, q, 0, out);                    \
 }
 
-ENCODE_FUNC(WebPEncodeRGB, WebPPictureImportRGB);
-ENCODE_FUNC(WebPEncodeBGR, WebPPictureImportBGR);
-ENCODE_FUNC(WebPEncodeRGBA, WebPPictureImportRGBA);
-ENCODE_FUNC(WebPEncodeBGRA, WebPPictureImportBGRA);
+ENCODE_FUNC(WebPEncodeRGB, WebPPictureImportRGB)
+ENCODE_FUNC(WebPEncodeBGR, WebPPictureImportBGR)
+ENCODE_FUNC(WebPEncodeRGBA, WebPPictureImportRGBA)
+ENCODE_FUNC(WebPEncodeBGRA, WebPPictureImportBGRA)
 
 #undef ENCODE_FUNC
 
@@ -1027,15 +280,11 @@ size_t NAME(const uint8_t* in, int w, int h, int bps, uint8_t** out) {       \
   return Encode(in, w, h, bps, IMPORTER, LOSSLESS_DEFAULT_QUALITY, 1, out);  \
 }
 
-LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessRGB, WebPPictureImportRGB);
-LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGR, WebPPictureImportBGR);
-LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessRGBA, WebPPictureImportRGBA);
-LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGRA, WebPPictureImportBGRA);
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessRGB, WebPPictureImportRGB)
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGR, WebPPictureImportBGR)
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessRGBA, WebPPictureImportRGBA)
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGRA, WebPPictureImportBGRA)
 
 #undef LOSSLESS_ENCODE_FUNC
 
 //------------------------------------------------------------------------------
-
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/quant.c b/drivers/webp/enc/quant.c
index ea153849c8..002c326b82 100644
--- a/drivers/webp/enc/quant.c
+++ b/drivers/webp/enc/quant.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 //   Quantization
@@ -11,6 +13,7 @@
 
 #include <assert.h>
 #include <math.h>
+#include <stdlib.h>  // for abs()
 
 #include "./vp8enci.h"
 #include "./cost.h"
@@ -22,16 +25,78 @@
 
 #define MID_ALPHA 64      // neutral value for susceptibility
 #define MIN_ALPHA 30      // lowest usable value for susceptibility
-#define MAX_ALPHA 100     // higher meaninful value for susceptibility
+#define MAX_ALPHA 100     // higher meaningful value for susceptibility
 
 #define SNS_TO_DQ 0.9     // Scaling constant between the sns value and the QP
                           // power-law modulation. Must be strictly less than 1.
 
+#define I4_PENALTY 4000   // Rate-penalty for quick i4/i16 decision
+
+// number of non-zero coeffs below which we consider the block very flat
+// (and apply a penalty to complex predictions)
+#define FLATNESS_LIMIT_I16 10      // I16 mode
+#define FLATNESS_LIMIT_I4  3       // I4 mode
+#define FLATNESS_LIMIT_UV  2       // UV mode
+#define FLATNESS_PENALTY   140     // roughly ~1bit per block
+
 #define MULT_8B(a, b) (((a) * (b) + 128) >> 8)
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
+// #define DEBUG_BLOCK
+
+//------------------------------------------------------------------------------
+
+#if defined(DEBUG_BLOCK)
+
+#include <stdio.h>
+#include <stdlib.h>
+
+static void PrintBlockInfo(const VP8EncIterator* const it,
+                           const VP8ModeScore* const rd) {
+  int i, j;
+  const int is_i16 = (it->mb_->type_ == 1);
+  printf("SOURCE / OUTPUT / ABS DELTA\n");
+  for (j = 0; j < 24; ++j) {
+    if (j == 16) printf("\n");   // newline before the U/V block
+    for (i = 0; i < 16; ++i) printf("%3d ", it->yuv_in_[i + j * BPS]);
+    printf("     ");
+    for (i = 0; i < 16; ++i) printf("%3d ", it->yuv_out_[i + j * BPS]);
+    printf("     ");
+    for (i = 0; i < 16; ++i) {
+      printf("%1d ", abs(it->yuv_out_[i + j * BPS] - it->yuv_in_[i + j * BPS]));
+    }
+    printf("\n");
+  }
+  printf("\nD:%d SD:%d R:%d H:%d nz:0x%x score:%d\n",
+    (int)rd->D, (int)rd->SD, (int)rd->R, (int)rd->H, (int)rd->nz,
+    (int)rd->score);
+  if (is_i16) {
+    printf("Mode: %d\n", rd->mode_i16);
+    printf("y_dc_levels:");
+    for (i = 0; i < 16; ++i) printf("%3d ", rd->y_dc_levels[i]);
+    printf("\n");
+  } else {
+    printf("Modes[16]: ");
+    for (i = 0; i < 16; ++i) printf("%d ", rd->modes_i4[i]);
+    printf("\n");
+  }
+  printf("y_ac_levels:\n");
+  for (j = 0; j < 16; ++j) {
+    for (i = is_i16 ? 1 : 0; i < 16; ++i) {
+      printf("%4d ", rd->y_ac_levels[j][i]);
+    }
+    printf("\n");
+  }
+  printf("\n");
+  printf("uv_levels (mode=%d):\n", rd->mode_uv);
+  for (j = 0; j < 8; ++j) {
+    for (i = 0; i < 16; ++i) {
+      printf("%4d ", rd->uv_levels[j][i]);
+    }
+    printf("\n");
+  }
+}
+
+#endif   // DEBUG_BLOCK
 
 //------------------------------------------------------------------------------
 
@@ -100,31 +165,13 @@ static const uint16_t kAcTable2[128] = {
   385, 393, 401, 409, 416, 424, 432, 440
 };
 
-static const uint16_t kCoeffThresh[16] = {
-  0,  10, 20, 30,
-  10, 20, 30, 30,
-  20, 30, 30, 30,
-  30, 30, 30, 30
-};
-
-// TODO(skal): tune more. Coeff thresholding?
-static const uint8_t kBiasMatrices[3][16] = {  // [3] = [luma-ac,luma-dc,chroma]
-  { 96, 96, 96, 96,
-    96, 96, 96, 96,
-    96, 96, 96, 96,
-    96, 96, 96, 96 },
-  { 96, 96, 96, 96,
-    96, 96, 96, 96,
-    96, 96, 96, 96,
-    96, 96, 96, 96 },
-  { 96, 96, 96, 96,
-    96, 96, 96, 96,
-    96, 96, 96, 96,
-    96, 96, 96, 96 }
+static const uint8_t kBiasMatrices[3][2] = {  // [luma-ac,luma-dc,chroma][dc,ac]
+  { 96, 110 }, { 96, 108 }, { 110, 115 }
 };
 
-// Sharpening by (slightly) raising the hi-frequency coeffs (only for trellis).
+// Sharpening by (slightly) raising the hi-frequency coeffs.
 // Hack-ish but helpful for mid-bitrate range. Use with care.
+#define SHARPEN_BITS 11  // number of descaling bits for sharpening bias
 static const uint8_t kFreqSharpening[16] = {
   0,  30, 60, 90,
   30, 60, 90, 90,
@@ -137,20 +184,30 @@ static const uint8_t kFreqSharpening[16] = {
 
 // Returns the average quantizer
 static int ExpandMatrix(VP8Matrix* const m, int type) {
-  int i;
-  int sum = 0;
+  int i, sum;
+  for (i = 0; i < 2; ++i) {
+    const int is_ac_coeff = (i > 0);
+    const int bias = kBiasMatrices[type][is_ac_coeff];
+    m->iq_[i] = (1 << QFIX) / m->q_[i];
+    m->bias_[i] = BIAS(bias);
+    // zthresh_ is the exact value such that QUANTDIV(coeff, iQ, B) is:
+    //   * zero if coeff <= zthresh
+    //   * non-zero if coeff > zthresh
+    m->zthresh_[i] = ((1 << QFIX) - 1 - m->bias_[i]) / m->iq_[i];
+  }
   for (i = 2; i < 16; ++i) {
     m->q_[i] = m->q_[1];
+    m->iq_[i] = m->iq_[1];
+    m->bias_[i] = m->bias_[1];
+    m->zthresh_[i] = m->zthresh_[1];
   }
-  for (i = 0; i < 16; ++i) {
-    const int j = kZigzag[i];
-    const int bias = kBiasMatrices[type][j];
-    m->iq_[j] = (1 << QFIX) / m->q_[j];
-    m->bias_[j] = BIAS(bias);
-    // TODO(skal): tune kCoeffThresh[]
-    m->zthresh_[j] = ((256 /*+ kCoeffThresh[j]*/ - bias) * m->q_[j] + 127) >> 8;
-    m->sharpen_[j] = (kFreqSharpening[j] * m->q_[j]) >> 11;
-    sum += m->q_[j];
+  for (sum = 0, i = 0; i < 16; ++i) {
+    if (type == 0) {  // we only use sharpening for AC luma coeffs
+      m->sharpen_[i] = (kFreqSharpening[i] * m->q_[i]) >> SHARPEN_BITS;
+    } else {
+      m->sharpen_[i] = 0;
+    }
+    sum += m->q_[i];
   }
   return (sum + 8) >> 4;
 }
@@ -178,17 +235,17 @@ static void SetupMatrices(VP8Encoder* enc) {
     q16 = ExpandMatrix(&m->y2_, 1);
     quv = ExpandMatrix(&m->uv_, 2);
 
-    // TODO: Switch to kLambda*[] tables?
-    {
-      m->lambda_i4_  = (3 * q4 * q4) >> 7;
-      m->lambda_i16_ = (3 * q16 * q16);
-      m->lambda_uv_  = (3 * quv * quv) >> 6;
-      m->lambda_mode_    = (1 * q4 * q4) >> 7;
-      m->lambda_trellis_i4_  = (7 * q4 * q4) >> 3;
-      m->lambda_trellis_i16_ = (q16 * q16) >> 2;
-      m->lambda_trellis_uv_  = (quv *quv) << 1;
-      m->tlambda_            = (tlambda_scale * q4) >> 5;
-    }
+    m->lambda_i4_          = (3 * q4 * q4) >> 7;
+    m->lambda_i16_         = (3 * q16 * q16);
+    m->lambda_uv_          = (3 * quv * quv) >> 6;
+    m->lambda_mode_        = (1 * q4 * q4) >> 7;
+    m->lambda_trellis_i4_  = (7 * q4 * q4) >> 3;
+    m->lambda_trellis_i16_ = (q16 * q16) >> 2;
+    m->lambda_trellis_uv_  = (quv *quv) << 1;
+    m->tlambda_            = (tlambda_scale * q4) >> 5;
+
+    m->min_disto_ = 10 * m->y1_.q_[0];   // quantization-aware min disto
+    m->max_edge_  = 0;
   }
 }
 
@@ -197,16 +254,21 @@ static void SetupMatrices(VP8Encoder* enc) {
 
 // Very small filter-strength values have close to no visual effect. So we can
 // save a little decoding-CPU by turning filtering off for these.
-#define FSTRENGTH_CUTOFF 3
+#define FSTRENGTH_CUTOFF 2
 
 static void SetupFilterStrength(VP8Encoder* const enc) {
   int i;
-  const int level0 = enc->config_->filter_strength;
+  // level0 is in [0..500]. Using '-f 50' as filter_strength is mid-filtering.
+  const int level0 = 5 * enc->config_->filter_strength;
   for (i = 0; i < NUM_MB_SEGMENTS; ++i) {
-    // Segments with lower quantizer will be less filtered. TODO: tune (wrt SNS)
-    const int level = level0 * 256 * enc->dqm_[i].quant_ / 128;
-    const int f = level / (256 + enc->dqm_[i].beta_);
-    enc->dqm_[i].fstrength_ = (f < FSTRENGTH_CUTOFF) ? 0 : (f > 63) ? 63 : f;
+    VP8SegmentInfo* const m = &enc->dqm_[i];
+    // We focus on the quantization of AC coeffs.
+    const int qstep = kAcTable[clip(m->quant_, 0, 127)] >> 2;
+    const int base_strength =
+        VP8FilterStrengthFromDelta(enc->filter_hdr_.sharpness_, qstep);
+    // Segments with lower complexity ('beta') will be less filtered.
+    const int f = base_strength * level0 / (256 + m->beta_);
+    m->fstrength_ = (f < FSTRENGTH_CUTOFF) ? 0 : (f > 63) ? 63 : f;
   }
   // We record the initial strength (mainly for the case of 1-segment only).
   enc->filter_hdr_.level_ = enc->dqm_[0].fstrength_;
@@ -224,28 +286,90 @@ static void SetupFilterStrength(VP8Encoder* const enc) {
 // We want to emulate jpeg-like behaviour where the expected "good" quality
 // is around q=75. Internally, our "good" middle is around c=50. So we
 // map accordingly using linear piece-wise function
-static double QualityToCompression(double q) {
-  const double c = q / 100.;
-  return (c < 0.75) ? c * (2. / 3.) : 2. * c - 1.;
+static double QualityToCompression(double c) {
+  const double linear_c = (c < 0.75) ? c * (2. / 3.) : 2. * c - 1.;
+  // The file size roughly scales as pow(quantizer, 3.). Actually, the
+  // exponent is somewhere between 2.8 and 3.2, but we're mostly interested
+  // in the mid-quant range. So we scale the compressibility inversely to
+  // this power-law: quant ~= compression ^ 1/3. This law holds well for
+  // low quant. Finer modeling for high-quant would make use of kAcTable[]
+  // more explicitly.
+  const double v = pow(linear_c, 1 / 3.);
+  return v;
+}
+
+static double QualityToJPEGCompression(double c, double alpha) {
+  // We map the complexity 'alpha' and quality setting 'c' to a compression
+  // exponent empirically matched to the compression curve of libjpeg6b.
+  // On average, the WebP output size will be roughly similar to that of a
+  // JPEG file compressed with same quality factor.
+  const double amin = 0.30;
+  const double amax = 0.85;
+  const double exp_min = 0.4;
+  const double exp_max = 0.9;
+  const double slope = (exp_min - exp_max) / (amax - amin);
+  // Linearly interpolate 'expn' from exp_min to exp_max
+  // in the [amin, amax] range.
+  const double expn = (alpha > amax) ? exp_min
+                    : (alpha < amin) ? exp_max
+                    : exp_max + slope * (alpha - amin);
+  const double v = pow(c, expn);
+  return v;
+}
+
+static int SegmentsAreEquivalent(const VP8SegmentInfo* const S1,
+                                 const VP8SegmentInfo* const S2) {
+  return (S1->quant_ == S2->quant_) && (S1->fstrength_ == S2->fstrength_);
+}
+
+static void SimplifySegments(VP8Encoder* const enc) {
+  int map[NUM_MB_SEGMENTS] = { 0, 1, 2, 3 };
+  const int num_segments = enc->segment_hdr_.num_segments_;
+  int num_final_segments = 1;
+  int s1, s2;
+  for (s1 = 1; s1 < num_segments; ++s1) {    // find similar segments
+    const VP8SegmentInfo* const S1 = &enc->dqm_[s1];
+    int found = 0;
+    // check if we already have similar segment
+    for (s2 = 0; s2 < num_final_segments; ++s2) {
+      const VP8SegmentInfo* const S2 = &enc->dqm_[s2];
+      if (SegmentsAreEquivalent(S1, S2)) {
+        found = 1;
+        break;
+      }
+    }
+    map[s1] = s2;
+    if (!found) {
+      if (num_final_segments != s1) {
+        enc->dqm_[num_final_segments] = enc->dqm_[s1];
+      }
+      ++num_final_segments;
+    }
+  }
+  if (num_final_segments < num_segments) {  // Remap
+    int i = enc->mb_w_ * enc->mb_h_;
+    while (i-- > 0) enc->mb_info_[i].segment_ = map[enc->mb_info_[i].segment_];
+    enc->segment_hdr_.num_segments_ = num_final_segments;
+    // Replicate the trailing segment infos (it's mostly cosmetics)
+    for (i = num_final_segments; i < num_segments; ++i) {
+      enc->dqm_[i] = enc->dqm_[num_final_segments - 1];
+    }
+  }
 }
 
 void VP8SetSegmentParams(VP8Encoder* const enc, float quality) {
   int i;
   int dq_uv_ac, dq_uv_dc;
-  const int num_segments = enc->config_->segments;
+  const int num_segments = enc->segment_hdr_.num_segments_;
   const double amp = SNS_TO_DQ * enc->config_->sns_strength / 100. / 128.;
-  const double c_base = QualityToCompression(quality);
+  const double Q = quality / 100.;
+  const double c_base = enc->config_->emulate_jpeg_size ?
+      QualityToJPEGCompression(Q, enc->alpha_ / 255.) :
+      QualityToCompression(Q);
   for (i = 0; i < num_segments; ++i) {
-    // The file size roughly scales as pow(quantizer, 3.). Actually, the
-    // exponent is somewhere between 2.8 and 3.2, but we're mostly interested
-    // in the mid-quant range. So we scale the compressibility inversely to
-    // this power-law: quant ~= compression ^ 1/3. This law holds well for
-    // low quant. Finer modelling for high-quant would make use of kAcTable[]
-    // more explicitely.
-    // Additionally, we modulate the base exponent 1/3 to accommodate for the
-    // quantization susceptibility and allow denser segments to be quantized
-    // more.
-    const double expn = (1. - amp * enc->dqm_[i].alpha_) / 3.;
+    // We modulate the base coefficient to accommodate for the quantization
+    // susceptibility and allow denser segments to be quantized more.
+    const double expn = 1. - amp * enc->dqm_[i].alpha_;
     const double c = pow(c_base, expn);
     const int q = (int)(127. * (1. - c));
     assert(expn > 0.);
@@ -271,7 +395,7 @@ void VP8SetSegmentParams(VP8Encoder* const enc, float quality) {
   dq_uv_ac = clip(dq_uv_ac, MIN_DQ_UV, MAX_DQ_UV);
   // We also boost the dc-uv-quant a little, based on sns-strength, since
   // U/V channels are quite more reactive to high quants (flat DC-blocks
-  // tend to appear, and are displeasant).
+  // tend to appear, and are unpleasant).
   dq_uv_dc = -4 * enc->config_->sns_strength / 100;
   dq_uv_dc = clip(dq_uv_dc, -15, 15);   // 4bit-signed max allowed
 
@@ -281,9 +405,11 @@ void VP8SetSegmentParams(VP8Encoder* const enc, float quality) {
   enc->dq_uv_dc_ = dq_uv_dc;
   enc->dq_uv_ac_ = dq_uv_ac;
 
-  SetupMatrices(enc);
-
   SetupFilterStrength(enc);   // initialize segments' filtering, eventually
+
+  if (num_segments > 1) SimplifySegments(enc);
+
+  SetupMatrices(enc);         // finalize quantization matrices
 }
 
 //------------------------------------------------------------------------------
@@ -299,16 +425,14 @@ const int VP8I4ModeOffsets[NUM_BMODES] = {
 };
 
 void VP8MakeLuma16Preds(const VP8EncIterator* const it) {
-  const VP8Encoder* const enc = it->enc_;
-  const uint8_t* const left = it->x_ ? enc->y_left_ : NULL;
-  const uint8_t* const top = it->y_ ? enc->y_top_ + it->x_ * 16 : NULL;
+  const uint8_t* const left = it->x_ ? it->y_left_ : NULL;
+  const uint8_t* const top = it->y_ ? it->y_top_ : NULL;
   VP8EncPredLuma16(it->yuv_p_, left, top);
 }
 
 void VP8MakeChroma8Preds(const VP8EncIterator* const it) {
-  const VP8Encoder* const enc = it->enc_;
-  const uint8_t* const left = it->x_ ? enc->u_left_ : NULL;
-  const uint8_t* const top = it->y_ ? enc->uv_top_ + it->x_ * 16 : NULL;
+  const uint8_t* const left = it->x_ ? it->u_left_ : NULL;
+  const uint8_t* const top = it->y_ ? it->uv_top_ : NULL;
   VP8EncPredChroma8(it->yuv_p_, left, top);
 }
 
@@ -320,23 +444,21 @@ void VP8MakeIntra4Preds(const VP8EncIterator* const it) {
 // Quantize
 
 // Layout:
-// +----+
-// |YYYY| 0
-// |YYYY| 4
-// |YYYY| 8
-// |YYYY| 12
-// +----+
-// |UUVV| 16
-// |UUVV| 20
-// +----+
-
-const int VP8Scan[16 + 4 + 4] = {
-  // Luma
+// +----+----+
+// |YYYY|UUVV| 0
+// |YYYY|UUVV| 4
+// |YYYY|....| 8
+// |YYYY|....| 12
+// +----+----+
+
+const int VP8Scan[16] = {  // Luma
   0 +  0 * BPS,  4 +  0 * BPS, 8 +  0 * BPS, 12 +  0 * BPS,
   0 +  4 * BPS,  4 +  4 * BPS, 8 +  4 * BPS, 12 +  4 * BPS,
   0 +  8 * BPS,  4 +  8 * BPS, 8 +  8 * BPS, 12 +  8 * BPS,
   0 + 12 * BPS,  4 + 12 * BPS, 8 + 12 * BPS, 12 + 12 * BPS,
+};
 
+static const int VP8ScanUV[4 + 4] = {
   0 + 0 * BPS,   4 + 0 * BPS, 0 + 4 * BPS,  4 + 4 * BPS,    // U
   8 + 0 * BPS,  12 + 0 * BPS, 8 + 4 * BPS, 12 + 4 * BPS     // V
 };
@@ -364,6 +486,7 @@ static void InitScore(VP8ModeScore* const rd) {
   rd->D  = 0;
   rd->SD = 0;
   rd->R  = 0;
+  rd->H  = 0;
   rd->nz = 0;
   rd->score = MAX_COST;
 }
@@ -372,6 +495,7 @@ static void CopyScore(VP8ModeScore* const dst, const VP8ModeScore* const src) {
   dst->D  = src->D;
   dst->SD = src->SD;
   dst->R  = src->R;
+  dst->H  = src->H;
   dst->nz = src->nz;      // note that nz is not accumulated, but just copied.
   dst->score = src->score;
 }
@@ -380,6 +504,7 @@ static void AddScore(VP8ModeScore* const dst, const VP8ModeScore* const src) {
   dst->D  += src->D;
   dst->SD += src->SD;
   dst->R  += src->R;
+  dst->H  += src->H;
   dst->nz |= src->nz;     // here, new nz bits are accumulated.
   dst->score += src->score;
 }
@@ -387,28 +512,31 @@ static void AddScore(VP8ModeScore* const dst, const VP8ModeScore* const src) {
 //------------------------------------------------------------------------------
 // Performs trellis-optimized quantization.
 
-// Trellis
-
+// Trellis node
 typedef struct {
-  int prev;        // best previous
-  int level;       // level
-  int sign;        // sign of coeff_i
-  score_t cost;    // bit cost
-  score_t error;   // distortion = sum of (|coeff_i| - level_i * Q_i)^2
-  int ctx;         // context (only depends on 'level'. Could be spared.)
+  int8_t prev;            // best previous node
+  int8_t sign;            // sign of coeff_i
+  int16_t level;          // level
 } Node;
 
+// Score state
+typedef struct {
+  score_t score;          // partial RD score
+  const uint16_t* costs;  // shortcut to cost tables
+} ScoreState;
+
 // If a coefficient was quantized to a value Q (using a neutral bias),
 // we test all alternate possibilities between [Q-MIN_DELTA, Q+MAX_DELTA]
 // We don't test negative values though.
 #define MIN_DELTA 0   // how much lower level to try
 #define MAX_DELTA 1   // how much higher
 #define NUM_NODES (MIN_DELTA + 1 + MAX_DELTA)
-#define NODE(n, l) (nodes[(n) + 1][(l) + MIN_DELTA])
+#define NODE(n, l) (nodes[(n)][(l) + MIN_DELTA])
+#define SCORE_STATE(n, l) (score_states[n][(l) + MIN_DELTA])
 
 static WEBP_INLINE void SetRDScore(int lambda, VP8ModeScore* const rd) {
   // TODO: incorporate the "* 256" in the tables?
-  rd->score = rd->R * lambda + 256 * (rd->D + rd->SD);
+  rd->score = (rd->R + rd->H) * lambda + 256 * (rd->D + rd->SD);
 }
 
 static WEBP_INLINE score_t RDScoreTrellis(int lambda, score_t rate,
@@ -416,34 +544,37 @@ static WEBP_INLINE score_t RDScoreTrellis(int lambda, score_t rate,
   return rate * lambda + 256 * distortion;
 }
 
-static int TrellisQuantizeBlock(const VP8EncIterator* const it,
+static int TrellisQuantizeBlock(const VP8Encoder* const enc,
                                 int16_t in[16], int16_t out[16],
                                 int ctx0, int coeff_type,
                                 const VP8Matrix* const mtx,
                                 int lambda) {
-  ProbaArray* const last_costs = it->enc_->proba_.coeffs_[coeff_type];
-  CostArray* const costs = it->enc_->proba_.level_cost_[coeff_type];
+  const ProbaArray* const probas = enc->proba_.coeffs_[coeff_type];
+  CostArrayPtr const costs =
+      (CostArrayPtr)enc->proba_.remapped_costs_[coeff_type];
   const int first = (coeff_type == 0) ? 1 : 0;
-  Node nodes[17][NUM_NODES];
+  Node nodes[16][NUM_NODES];
+  ScoreState score_states[2][NUM_NODES];
+  ScoreState* ss_cur = &SCORE_STATE(0, MIN_DELTA);
+  ScoreState* ss_prev = &SCORE_STATE(1, MIN_DELTA);
   int best_path[3] = {-1, -1, -1};   // store best-last/best-level/best-previous
   score_t best_score;
-  int best_node;
-  int last = first - 1;
-  int n, m, p, nz;
+  int n, m, p, last;
 
   {
     score_t cost;
-    score_t max_error;
     const int thresh = mtx->q_[1] * mtx->q_[1] / 4;
-    const int last_proba = last_costs[VP8EncBands[first]][ctx0][0];
+    const int last_proba = probas[VP8EncBands[first]][ctx0][0];
 
-    // compute maximal distortion.
-    max_error = 0;
-    for (n = first; n < 16; ++n) {
-      const int j  = kZigzag[n];
+    // compute the position of the last interesting coefficient
+    last = first - 1;
+    for (n = 15; n >= first; --n) {
+      const int j = kZigzag[n];
       const int err = in[j] * in[j];
-      max_error += kWeightTrellis[j] * err;
-      if (err > thresh) last = n;
+      if (err > thresh) {
+        last = n;
+        break;
+      }
     }
     // we don't need to go inspect up to n = 16 coeffs. We can just go up
     // to last + 1 (inclusive) without losing much.
@@ -451,93 +582,95 @@ static int TrellisQuantizeBlock(const VP8EncIterator* const it,
 
     // compute 'skip' score. This is the max score one can do.
     cost = VP8BitCost(0, last_proba);
-    best_score = RDScoreTrellis(lambda, cost, max_error);
+    best_score = RDScoreTrellis(lambda, cost, 0);
 
     // initialize source node.
-    n = first - 1;
     for (m = -MIN_DELTA; m <= MAX_DELTA; ++m) {
-      NODE(n, m).cost = 0;
-      NODE(n, m).error = max_error;
-      NODE(n, m).ctx = ctx0;
+      const score_t rate = (ctx0 == 0) ? VP8BitCost(1, last_proba) : 0;
+      ss_cur[m].score = RDScoreTrellis(lambda, rate, 0);
+      ss_cur[m].costs = costs[first][ctx0];
     }
   }
 
   // traverse trellis.
   for (n = first; n <= last; ++n) {
-    const int j  = kZigzag[n];
-    const int Q  = mtx->q_[j];
-    const int iQ = mtx->iq_[j];
-    const int B = BIAS(0x00);     // neutral bias
+    const int j = kZigzag[n];
+    const uint32_t Q  = mtx->q_[j];
+    const uint32_t iQ = mtx->iq_[j];
+    const uint32_t B = BIAS(0x00);     // neutral bias
     // note: it's important to take sign of the _original_ coeff,
     // so we don't have to consider level < 0 afterward.
     const int sign = (in[j] < 0);
-    int coeff0 = (sign ? -in[j] : in[j]) + mtx->sharpen_[j];
-    int level0;
-    if (coeff0 > 2047) coeff0 = 2047;
+    const uint32_t coeff0 = (sign ? -in[j] : in[j]) + mtx->sharpen_[j];
+    int level0 = QUANTDIV(coeff0, iQ, B);
+    if (level0 > MAX_LEVEL) level0 = MAX_LEVEL;
+
+    {   // Swap current and previous score states
+      ScoreState* const tmp = ss_cur;
+      ss_cur = ss_prev;
+      ss_prev = tmp;
+    }
 
-    level0 = QUANTDIV(coeff0, iQ, B);
     // test all alternate level values around level0.
     for (m = -MIN_DELTA; m <= MAX_DELTA; ++m) {
       Node* const cur = &NODE(n, m);
-      int delta_error, new_error;
-      score_t cur_score = MAX_COST;
       int level = level0 + m;
-      int last_proba;
-
-      cur->sign = sign;
-      cur->level = level;
-      cur->ctx = (level == 0) ? 0 : (level == 1) ? 1 : 2;
-      if (level >= 2048 || level < 0) {   // node is dead?
-        cur->cost = MAX_COST;
+      const int ctx = (level > 2) ? 2 : level;
+      const int band = VP8EncBands[n + 1];
+      score_t base_score, last_pos_score;
+      score_t best_cur_score = MAX_COST;
+      int best_prev = 0;   // default, in case
+
+      ss_cur[m].score = MAX_COST;
+      ss_cur[m].costs = costs[n + 1][ctx];
+      if (level > MAX_LEVEL || level < 0) {   // node is dead?
         continue;
       }
-      last_proba = last_costs[VP8EncBands[n + 1]][cur->ctx][0];
 
-      // Compute delta_error = how much coding this level will
-      // subtract as distortion to max_error
-      new_error = coeff0 - level * Q;
-      delta_error =
-        kWeightTrellis[j] * (coeff0 * coeff0 - new_error * new_error);
+      // Compute extra rate cost if last coeff's position is < 15
+      {
+        const score_t last_pos_cost =
+            (n < 15) ? VP8BitCost(0, probas[band][ctx][0]) : 0;
+        last_pos_score = RDScoreTrellis(lambda, last_pos_cost, 0);
+      }
+
+      {
+        // Compute delta_error = how much coding this level will
+        // subtract to max_error as distortion.
+        // Here, distortion = sum of (|coeff_i| - level_i * Q_i)^2
+        const int new_error = coeff0 - level * Q;
+        const int delta_error =
+            kWeightTrellis[j] * (new_error * new_error - coeff0 * coeff0);
+        base_score = RDScoreTrellis(lambda, 0, delta_error);
+      }
 
       // Inspect all possible non-dead predecessors. Retain only the best one.
       for (p = -MIN_DELTA; p <= MAX_DELTA; ++p) {
-        const Node* const prev = &NODE(n - 1, p);
-        const int prev_ctx = prev->ctx;
-        const uint16_t* const tcost = costs[VP8EncBands[n]][prev_ctx];
-        const score_t total_error = prev->error - delta_error;
-        score_t cost, base_cost, score;
-
-        if (prev->cost >= MAX_COST) {   // dead node?
-          continue;
-        }
-
-        // Base cost of both terminal/non-terminal
-        base_cost = prev->cost + VP8LevelCost(tcost, level);
-
+        // Dead nodes (with ss_prev[p].score >= MAX_COST) are automatically
+        // eliminated since their score can't be better than the current best.
+        const score_t cost = VP8LevelCost(ss_prev[p].costs, level);
         // Examine node assuming it's a non-terminal one.
-        cost = base_cost;
-        if (level && n < 15) {
-          cost += VP8BitCost(1, last_proba);
+        const score_t score =
+            base_score + ss_prev[p].score + RDScoreTrellis(lambda, cost, 0);
+        if (score < best_cur_score) {
+          best_cur_score = score;
+          best_prev = p;
         }
-        score = RDScoreTrellis(lambda, cost, total_error);
-        if (score < cur_score) {
-          cur_score = score;
-          cur->cost  = cost;
-          cur->error = total_error;
-          cur->prev  = p;
-        }
-
-        // Now, record best terminal node (and thus best entry in the graph).
-        if (level) {
-          cost = base_cost;
-          if (n < 15) cost += VP8BitCost(0, last_proba);
-          score = RDScoreTrellis(lambda, cost, total_error);
-          if (score < best_score) {
-            best_score = score;
-            best_path[0] = n;   // best eob position
-            best_path[1] = m;   // best level
-            best_path[2] = p;   // best predecessor
-          }
+      }
+      // Store best finding in current node.
+      cur->sign = sign;
+      cur->level = level;
+      cur->prev = best_prev;
+      ss_cur[m].score = best_cur_score;
+
+      // Now, record best terminal node (and thus best entry in the graph).
+      if (level != 0) {
+        const score_t score = best_cur_score + last_pos_score;
+        if (score < best_score) {
+          best_score = score;
+          best_path[0] = n;                     // best eob position
+          best_path[1] = m;                     // best node index
+          best_path[2] = best_prev;             // best predecessor
         }
       }
     }
@@ -550,23 +683,25 @@ static int TrellisQuantizeBlock(const VP8EncIterator* const it,
     return 0;   // skip!
   }
 
-  // Unwind the best path.
-  // Note: best-prev on terminal node is not necessarily equal to the
-  // best_prev for non-terminal. So we patch best_path[2] in.
-  n = best_path[0];
-  best_node = best_path[1];
-  NODE(n, best_node).prev = best_path[2];   // force best-prev for terminal
-  nz = 0;
-
-  for (; n >= first; --n) {
-    const Node* const node = &NODE(n, best_node);
-    const int j = kZigzag[n];
-    out[n] = node->sign ? -node->level : node->level;
-    nz |= (node->level != 0);
-    in[j] = out[n] * mtx->q_[j];
-    best_node = node->prev;
+  {
+    // Unwind the best path.
+    // Note: best-prev on terminal node is not necessarily equal to the
+    // best_prev for non-terminal. So we patch best_path[2] in.
+    int nz = 0;
+    int best_node = best_path[1];
+    n = best_path[0];
+    NODE(n, best_node).prev = best_path[2];   // force best-prev for terminal
+
+    for (; n >= first; --n) {
+      const Node* const node = &NODE(n, best_node);
+      const int j = kZigzag[n];
+      out[n] = node->sign ? -node->level : node->level;
+      nz |= node->level;
+      in[j] = out[n] * mtx->q_[j];
+      best_node = node->prev;
+    }
+    return (nz != 0);
   }
-  return nz;
 }
 
 #undef NODE
@@ -582,17 +717,17 @@ static int ReconstructIntra16(VP8EncIterator* const it,
                               int mode) {
   const VP8Encoder* const enc = it->enc_;
   const uint8_t* const ref = it->yuv_p_ + VP8I16ModeOffsets[mode];
-  const uint8_t* const src = it->yuv_in_ + Y_OFF;
+  const uint8_t* const src = it->yuv_in_ + Y_OFF_ENC;
   const VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
   int nz = 0;
   int n;
   int16_t tmp[16][16], dc_tmp[16];
 
-  for (n = 0; n < 16; ++n) {
-    VP8FTransform(src + VP8Scan[n], ref + VP8Scan[n], tmp[n]);
+  for (n = 0; n < 16; n += 2) {
+    VP8FTransform2(src + VP8Scan[n], ref + VP8Scan[n], tmp[n]);
   }
   VP8FTransformWHT(tmp[0], dc_tmp);
-  nz |= VP8EncQuantizeBlock(dc_tmp, rd->y_dc_levels, 0, &dqm->y2_) << 24;
+  nz |= VP8EncQuantizeBlockWHT(dc_tmp, rd->y_dc_levels, &dqm->y2_) << 24;
 
   if (DO_TRELLIS_I16 && it->do_trellis_) {
     int x, y;
@@ -601,20 +736,26 @@ static int ReconstructIntra16(VP8EncIterator* const it,
       for (x = 0; x < 4; ++x, ++n) {
         const int ctx = it->top_nz_[x] + it->left_nz_[y];
         const int non_zero =
-           TrellisQuantizeBlock(it, tmp[n], rd->y_ac_levels[n], ctx, 0,
-                                &dqm->y1_, dqm->lambda_trellis_i16_);
+            TrellisQuantizeBlock(enc, tmp[n], rd->y_ac_levels[n], ctx, 0,
+                                 &dqm->y1_, dqm->lambda_trellis_i16_);
         it->top_nz_[x] = it->left_nz_[y] = non_zero;
+        rd->y_ac_levels[n][0] = 0;
         nz |= non_zero << n;
       }
     }
   } else {
-    for (n = 0; n < 16; ++n) {
-      nz |= VP8EncQuantizeBlock(tmp[n], rd->y_ac_levels[n], 1, &dqm->y1_) << n;
+    for (n = 0; n < 16; n += 2) {
+      // Zero-out the first coeff, so that: a) nz is correct below, and
+      // b) finding 'last' non-zero coeffs in SetResidualCoeffs() is simplified.
+      tmp[n][0] = tmp[n + 1][0] = 0;
+      nz |= VP8EncQuantize2Blocks(tmp[n], rd->y_ac_levels[n], &dqm->y1_) << n;
+      assert(rd->y_ac_levels[n + 0][0] == 0);
+      assert(rd->y_ac_levels[n + 1][0] == 0);
     }
   }
 
   // Transform back
-  VP8ITransformWHT(dc_tmp, tmp[0]);
+  VP8TransformWHT(dc_tmp, tmp[0]);
   for (n = 0; n < 16; n += 2) {
     VP8ITransform(ref + VP8Scan[n], tmp[n], yuv_out + VP8Scan[n], 1);
   }
@@ -637,10 +778,10 @@ static int ReconstructIntra4(VP8EncIterator* const it,
   if (DO_TRELLIS_I4 && it->do_trellis_) {
     const int x = it->i4_ & 3, y = it->i4_ >> 2;
     const int ctx = it->top_nz_[x] + it->left_nz_[y];
-    nz = TrellisQuantizeBlock(it, tmp, levels, ctx, 3, &dqm->y1_,
+    nz = TrellisQuantizeBlock(enc, tmp, levels, ctx, 3, &dqm->y1_,
                               dqm->lambda_trellis_i4_);
   } else {
-    nz = VP8EncQuantizeBlock(tmp, levels, 0, &dqm->y1_);
+    nz = VP8EncQuantizeBlock(tmp, levels, &dqm->y1_);
   }
   VP8ITransform(ref, tmp, yuv_out, 0);
   return nz;
@@ -650,14 +791,14 @@ static int ReconstructUV(VP8EncIterator* const it, VP8ModeScore* const rd,
                          uint8_t* const yuv_out, int mode) {
   const VP8Encoder* const enc = it->enc_;
   const uint8_t* const ref = it->yuv_p_ + VP8UVModeOffsets[mode];
-  const uint8_t* const src = it->yuv_in_ + U_OFF;
+  const uint8_t* const src = it->yuv_in_ + U_OFF_ENC;
   const VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
   int nz = 0;
   int n;
   int16_t tmp[8][16];
 
-  for (n = 0; n < 8; ++n) {
-    VP8FTransform(src + VP8Scan[16 + n], ref + VP8Scan[16 + n], tmp[n]);
+  for (n = 0; n < 8; n += 2) {
+    VP8FTransform2(src + VP8ScanUV[n], ref + VP8ScanUV[n], tmp[n]);
   }
   if (DO_TRELLIS_UV && it->do_trellis_) {
     int ch, x, y;
@@ -666,28 +807,45 @@ static int ReconstructUV(VP8EncIterator* const it, VP8ModeScore* const rd,
         for (x = 0; x < 2; ++x, ++n) {
           const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
           const int non_zero =
-            TrellisQuantizeBlock(it, tmp[n], rd->uv_levels[n], ctx, 2,
-                                 &dqm->uv_, dqm->lambda_trellis_uv_);
+              TrellisQuantizeBlock(enc, tmp[n], rd->uv_levels[n], ctx, 2,
+                                   &dqm->uv_, dqm->lambda_trellis_uv_);
           it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] = non_zero;
           nz |= non_zero << n;
         }
       }
     }
   } else {
-    for (n = 0; n < 8; ++n) {
-      nz |= VP8EncQuantizeBlock(tmp[n], rd->uv_levels[n], 0, &dqm->uv_) << n;
+    for (n = 0; n < 8; n += 2) {
+      nz |= VP8EncQuantize2Blocks(tmp[n], rd->uv_levels[n], &dqm->uv_) << n;
     }
   }
 
   for (n = 0; n < 8; n += 2) {
-    VP8ITransform(ref + VP8Scan[16 + n], tmp[n], yuv_out + VP8Scan[16 + n], 1);
+    VP8ITransform(ref + VP8ScanUV[n], tmp[n], yuv_out + VP8ScanUV[n], 1);
   }
   return (nz << 16);
 }
 
 //------------------------------------------------------------------------------
 // RD-opt decision. Reconstruct each modes, evalue distortion and bit-cost.
-// Pick the mode is lower RD-cost = Rate + lamba * Distortion.
+// Pick the mode is lower RD-cost = Rate + lambda * Distortion.
+
+static void StoreMaxDelta(VP8SegmentInfo* const dqm, const int16_t DCs[16]) {
+  // We look at the first three AC coefficients to determine what is the average
+  // delta between each sub-4x4 block.
+  const int v0 = abs(DCs[1]);
+  const int v1 = abs(DCs[4]);
+  const int v2 = abs(DCs[5]);
+  int max_v = (v0 > v1) ? v1 : v0;
+  max_v = (v2 > max_v) ? v2 : max_v;
+  if (max_v > dqm->max_edge_) dqm->max_edge_ = max_v;
+}
+
+static void SwapModeScore(VP8ModeScore** a, VP8ModeScore** b) {
+  VP8ModeScore* const tmp = *a;
+  *a = *b;
+  *b = tmp;
+}
 
 static void SwapPtr(uint8_t** a, uint8_t** b) {
   uint8_t* const tmp = *a;
@@ -699,43 +857,69 @@ static void SwapOut(VP8EncIterator* const it) {
   SwapPtr(&it->yuv_out_, &it->yuv_out2_);
 }
 
-static void PickBestIntra16(VP8EncIterator* const it, VP8ModeScore* const rd) {
-  const VP8Encoder* const enc = it->enc_;
-  const VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
+static score_t IsFlat(const int16_t* levels, int num_blocks, score_t thresh) {
+  score_t score = 0;
+  while (num_blocks-- > 0) {      // TODO(skal): refine positional scoring?
+    int i;
+    for (i = 1; i < 16; ++i) {    // omit DC, we're only interested in AC
+      score += (levels[i] != 0);
+      if (score > thresh) return 0;
+    }
+    levels += 16;
+  }
+  return 1;
+}
+
+static void PickBestIntra16(VP8EncIterator* const it, VP8ModeScore* rd) {
+  const int kNumBlocks = 16;
+  VP8SegmentInfo* const dqm = &it->enc_->dqm_[it->mb_->segment_];
   const int lambda = dqm->lambda_i16_;
   const int tlambda = dqm->tlambda_;
-  const uint8_t* const src = it->yuv_in_ + Y_OFF;
-  VP8ModeScore rd16;
+  const uint8_t* const src = it->yuv_in_ + Y_OFF_ENC;
+  VP8ModeScore rd_tmp;
+  VP8ModeScore* rd_cur = &rd_tmp;
+  VP8ModeScore* rd_best = rd;
   int mode;
 
   rd->mode_i16 = -1;
-  for (mode = 0; mode < 4; ++mode) {
-    uint8_t* const tmp_dst = it->yuv_out2_ + Y_OFF;  // scratch buffer
-    int nz;
+  for (mode = 0; mode < NUM_PRED_MODES; ++mode) {
+    uint8_t* const tmp_dst = it->yuv_out2_ + Y_OFF_ENC;  // scratch buffer
+    rd_cur->mode_i16 = mode;
 
     // Reconstruct
-    nz = ReconstructIntra16(it, &rd16, tmp_dst, mode);
+    rd_cur->nz = ReconstructIntra16(it, rd_cur, tmp_dst, mode);
 
     // Measure RD-score
-    rd16.D = VP8SSE16x16(src, tmp_dst);
-    rd16.SD = tlambda ? MULT_8B(tlambda, VP8TDisto16x16(src, tmp_dst, kWeightY))
-            : 0;
-    rd16.R = VP8GetCostLuma16(it, &rd16);
-    rd16.R += VP8FixedCostsI16[mode];
+    rd_cur->D = VP8SSE16x16(src, tmp_dst);
+    rd_cur->SD =
+        tlambda ? MULT_8B(tlambda, VP8TDisto16x16(src, tmp_dst, kWeightY)) : 0;
+    rd_cur->H = VP8FixedCostsI16[mode];
+    rd_cur->R = VP8GetCostLuma16(it, rd_cur);
+    if (mode > 0 &&
+        IsFlat(rd_cur->y_ac_levels[0], kNumBlocks, FLATNESS_LIMIT_I16)) {
+      // penalty to avoid flat area to be mispredicted by complex mode
+      rd_cur->R += FLATNESS_PENALTY * kNumBlocks;
+    }
 
     // Since we always examine Intra16 first, we can overwrite *rd directly.
-    SetRDScore(lambda, &rd16);
-    if (mode == 0 || rd16.score < rd->score) {
-      CopyScore(rd, &rd16);
-      rd->mode_i16 = mode;
-      rd->nz = nz;
-      memcpy(rd->y_ac_levels, rd16.y_ac_levels, sizeof(rd16.y_ac_levels));
-      memcpy(rd->y_dc_levels, rd16.y_dc_levels, sizeof(rd16.y_dc_levels));
+    SetRDScore(lambda, rd_cur);
+    if (mode == 0 || rd_cur->score < rd_best->score) {
+      SwapModeScore(&rd_cur, &rd_best);
       SwapOut(it);
     }
   }
+  if (rd_best != rd) {
+    memcpy(rd, rd_best, sizeof(*rd));
+  }
   SetRDScore(dqm->lambda_mode_, rd);   // finalize score for mode decision.
   VP8SetIntra16Mode(it, rd->mode_i16);
+
+  // we have a blocky macroblock (only DCs are non-zero) with fairly high
+  // distortion, record max delta so we can later adjust the minimal filtering
+  // strength needed to smooth these blocks out.
+  if ((rd->nz & 0xffff) == 0 && rd->D > dqm->min_disto_) {
+    StoreMaxDelta(dqm, rd->y_dc_levels);
+  }
 }
 
 //------------------------------------------------------------------------------
@@ -755,8 +939,8 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
   const VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
   const int lambda = dqm->lambda_i4_;
   const int tlambda = dqm->tlambda_;
-  const uint8_t* const src0 = it->yuv_in_ + Y_OFF;
-  uint8_t* const best_blocks = it->yuv_out2_ + Y_OFF;
+  const uint8_t* const src0 = it->yuv_in_ + Y_OFF_ENC;
+  uint8_t* const best_blocks = it->yuv_out2_ + Y_OFF_ENC;
   int total_header_bits = 0;
   VP8ModeScore rd_best;
 
@@ -765,9 +949,11 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
   }
 
   InitScore(&rd_best);
-  rd_best.score = 211;  // '211' is the value of VP8BitCost(0, 145)
+  rd_best.H = 211;  // '211' is the value of VP8BitCost(0, 145)
+  SetRDScore(dqm->lambda_mode_, &rd_best);
   VP8IteratorStartI4(it);
   do {
+    const int kNumBlocks = 1;
     VP8ModeScore rd_i4;
     int mode;
     int best_mode = -1;
@@ -791,27 +977,44 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
       rd_tmp.SD =
           tlambda ? MULT_8B(tlambda, VP8TDisto4x4(src, tmp_dst, kWeightY))
                   : 0;
-      rd_tmp.R = VP8GetCostLuma4(it, tmp_levels);
-      rd_tmp.R += mode_costs[mode];
+      rd_tmp.H = mode_costs[mode];
+
+      // Add flatness penalty
+      if (mode > 0 && IsFlat(tmp_levels, kNumBlocks, FLATNESS_LIMIT_I4)) {
+        rd_tmp.R = FLATNESS_PENALTY * kNumBlocks;
+      } else {
+        rd_tmp.R = 0;
+      }
 
+      // early-out check
       SetRDScore(lambda, &rd_tmp);
+      if (best_mode >= 0 && rd_tmp.score >= rd_i4.score) continue;
+
+      // finish computing score
+      rd_tmp.R += VP8GetCostLuma4(it, tmp_levels);
+      SetRDScore(lambda, &rd_tmp);
+
       if (best_mode < 0 || rd_tmp.score < rd_i4.score) {
         CopyScore(&rd_i4, &rd_tmp);
         best_mode = mode;
         SwapPtr(&tmp_dst, &best_block);
-        memcpy(rd_best.y_ac_levels[it->i4_], tmp_levels, sizeof(tmp_levels));
+        memcpy(rd_best.y_ac_levels[it->i4_], tmp_levels,
+               sizeof(rd_best.y_ac_levels[it->i4_]));
       }
     }
     SetRDScore(dqm->lambda_mode_, &rd_i4);
     AddScore(&rd_best, &rd_i4);
-    total_header_bits += mode_costs[best_mode];
-    if (rd_best.score >= rd->score ||
-        total_header_bits > enc->max_i4_header_bits_) {
+    if (rd_best.score >= rd->score) {
+      return 0;
+    }
+    total_header_bits += (int)rd_i4.H;   // <- equal to mode_costs[best_mode];
+    if (total_header_bits > enc->max_i4_header_bits_) {
       return 0;
     }
     // Copy selected samples if not in the right place already.
-    if (best_block != best_blocks + VP8Scan[it->i4_])
+    if (best_block != best_blocks + VP8Scan[it->i4_]) {
       VP8Copy4x4(best_block, best_blocks + VP8Scan[it->i4_]);
+    }
     rd->modes_i4[it->i4_] = best_mode;
     it->top_nz_[it->i4_ & 3] = it->left_nz_[it->i4_ >> 2] = (rd_i4.nz ? 1 : 0);
   } while (VP8IteratorRotateI4(it, best_blocks));
@@ -827,18 +1030,19 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
 //------------------------------------------------------------------------------
 
 static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) {
-  const VP8Encoder* const enc = it->enc_;
-  const VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
+  const int kNumBlocks = 8;
+  const VP8SegmentInfo* const dqm = &it->enc_->dqm_[it->mb_->segment_];
   const int lambda = dqm->lambda_uv_;
-  const uint8_t* const src = it->yuv_in_ + U_OFF;
-  uint8_t* const tmp_dst = it->yuv_out2_ + U_OFF;  // scratch buffer
-  uint8_t* const dst0 = it->yuv_out_ + U_OFF;
+  const uint8_t* const src = it->yuv_in_ + U_OFF_ENC;
+  uint8_t* tmp_dst = it->yuv_out2_ + U_OFF_ENC;  // scratch buffer
+  uint8_t* dst0 = it->yuv_out_ + U_OFF_ENC;
+  uint8_t* dst = dst0;
   VP8ModeScore rd_best;
   int mode;
 
   rd->mode_uv = -1;
   InitScore(&rd_best);
-  for (mode = 0; mode < 4; ++mode) {
+  for (mode = 0; mode < NUM_PRED_MODES; ++mode) {
     VP8ModeScore rd_uv;
 
     // Reconstruct
@@ -847,19 +1051,25 @@ static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) {
     // Compute RD-score
     rd_uv.D  = VP8SSE16x8(src, tmp_dst);
     rd_uv.SD = 0;    // TODO: should we call TDisto? it tends to flatten areas.
+    rd_uv.H  = VP8FixedCostsUV[mode];
     rd_uv.R  = VP8GetCostUV(it, &rd_uv);
-    rd_uv.R += VP8FixedCostsUV[mode];
+    if (mode > 0 && IsFlat(rd_uv.uv_levels[0], kNumBlocks, FLATNESS_LIMIT_UV)) {
+      rd_uv.R += FLATNESS_PENALTY * kNumBlocks;
+    }
 
     SetRDScore(lambda, &rd_uv);
     if (mode == 0 || rd_uv.score < rd_best.score) {
       CopyScore(&rd_best, &rd_uv);
       rd->mode_uv = mode;
       memcpy(rd->uv_levels, rd_uv.uv_levels, sizeof(rd->uv_levels));
-      memcpy(dst0, tmp_dst, UV_SIZE);   //  TODO: SwapUVOut() ?
+      SwapPtr(&dst, &tmp_dst);
     }
   }
   VP8SetIntraUVMode(it, rd->mode_uv);
   AddScore(rd, &rd_best);
+  if (dst != dst0) {   // copy 16x8 block if needed
+    VP8Copy16x8(dst, dst0);
+  }
 }
 
 //------------------------------------------------------------------------------
@@ -867,33 +1077,88 @@ static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) {
 
 static void SimpleQuantize(VP8EncIterator* const it, VP8ModeScore* const rd) {
   const VP8Encoder* const enc = it->enc_;
-  const int i16 = (it->mb_->type_ == 1);
+  const int is_i16 = (it->mb_->type_ == 1);
   int nz = 0;
 
-  if (i16) {
-    nz = ReconstructIntra16(it, rd, it->yuv_out_ + Y_OFF, it->preds_[0]);
+  if (is_i16) {
+    nz = ReconstructIntra16(it, rd, it->yuv_out_ + Y_OFF_ENC, it->preds_[0]);
   } else {
     VP8IteratorStartI4(it);
     do {
       const int mode =
           it->preds_[(it->i4_ & 3) + (it->i4_ >> 2) * enc->preds_w_];
-      const uint8_t* const src = it->yuv_in_ + Y_OFF + VP8Scan[it->i4_];
-      uint8_t* const dst = it->yuv_out_ + Y_OFF + VP8Scan[it->i4_];
+      const uint8_t* const src = it->yuv_in_ + Y_OFF_ENC + VP8Scan[it->i4_];
+      uint8_t* const dst = it->yuv_out_ + Y_OFF_ENC + VP8Scan[it->i4_];
       VP8MakeIntra4Preds(it);
       nz |= ReconstructIntra4(it, rd->y_ac_levels[it->i4_],
                               src, dst, mode) << it->i4_;
-    } while (VP8IteratorRotateI4(it, it->yuv_out_ + Y_OFF));
+    } while (VP8IteratorRotateI4(it, it->yuv_out_ + Y_OFF_ENC));
   }
 
-  nz |= ReconstructUV(it, rd, it->yuv_out_ + U_OFF, it->mb_->uv_mode_);
+  nz |= ReconstructUV(it, rd, it->yuv_out_ + U_OFF_ENC, it->mb_->uv_mode_);
   rd->nz = nz;
 }
 
+// Refine intra16/intra4 sub-modes based on distortion only (not rate).
+static void DistoRefine(VP8EncIterator* const it, int try_both_i4_i16) {
+  const int is_i16 = (it->mb_->type_ == 1);
+  score_t best_score = MAX_COST;
+
+  if (try_both_i4_i16 || is_i16) {
+    int mode;
+    int best_mode = -1;
+    for (mode = 0; mode < NUM_PRED_MODES; ++mode) {
+      const uint8_t* const ref = it->yuv_p_ + VP8I16ModeOffsets[mode];
+      const uint8_t* const src = it->yuv_in_ + Y_OFF_ENC;
+      const score_t score = VP8SSE16x16(src, ref);
+      if (score < best_score) {
+        best_mode = mode;
+        best_score = score;
+      }
+    }
+    VP8SetIntra16Mode(it, best_mode);
+  }
+  if (try_both_i4_i16 || !is_i16) {
+    uint8_t modes_i4[16];
+    // We don't evaluate the rate here, but just account for it through a
+    // constant penalty (i4 mode usually needs more bits compared to i16).
+    score_t score_i4 = (score_t)I4_PENALTY;
+
+    VP8IteratorStartI4(it);
+    do {
+      int mode;
+      int best_sub_mode = -1;
+      score_t best_sub_score = MAX_COST;
+      const uint8_t* const src = it->yuv_in_ + Y_OFF_ENC + VP8Scan[it->i4_];
+
+      // TODO(skal): we don't really need the prediction pixels here,
+      // but just the distortion against 'src'.
+      VP8MakeIntra4Preds(it);
+      for (mode = 0; mode < NUM_BMODES; ++mode) {
+        const uint8_t* const ref = it->yuv_p_ + VP8I4ModeOffsets[mode];
+        const score_t score = VP8SSE4x4(src, ref);
+        if (score < best_sub_score) {
+          best_sub_mode = mode;
+          best_sub_score = score;
+        }
+      }
+      modes_i4[it->i4_] = best_sub_mode;
+      score_i4 += best_sub_score;
+      if (score_i4 >= best_score) break;
+    } while (VP8IteratorRotateI4(it, it->yuv_in_ + Y_OFF_ENC));
+    if (score_i4 < best_score) {
+      VP8SetIntra4Mode(it, modes_i4);
+    }
+  }
+}
+
 //------------------------------------------------------------------------------
 // Entry point
 
-int VP8Decimate(VP8EncIterator* const it, VP8ModeScore* const rd, int rd_opt) {
+int VP8Decimate(VP8EncIterator* const it, VP8ModeScore* const rd,
+                VP8RDLevel rd_opt) {
   int is_skipped;
+  const int method = it->enc_->method_;
 
   InitScore(rd);
 
@@ -902,22 +1167,21 @@ int VP8Decimate(VP8EncIterator* const it, VP8ModeScore* const rd, int rd_opt) {
   VP8MakeLuma16Preds(it);
   VP8MakeChroma8Preds(it);
 
-  // for rd_opt = 2, we perform trellis-quant on the final decision only.
-  // for rd_opt > 2, we use it for every scoring (=much slower).
-  if (rd_opt > 0) {
-    it->do_trellis_ = (rd_opt > 2);
+  if (rd_opt > RD_OPT_NONE) {
+    it->do_trellis_ = (rd_opt >= RD_OPT_TRELLIS_ALL);
     PickBestIntra16(it, rd);
-    if (it->enc_->method_ >= 2) {
+    if (method >= 2) {
       PickBestIntra4(it, rd);
     }
     PickBestUV(it, rd);
-    if (rd_opt == 2) {
+    if (rd_opt == RD_OPT_TRELLIS) {   // finish off with trellis-optim now
       it->do_trellis_ = 1;
       SimpleQuantize(it, rd);
     }
   } else {
-    // TODO: for method_ == 2, pick the best intra4/intra16 based on SSE
-    it->do_trellis_ = (it->enc_->method_ == 2);
+    // For method == 2, pick the best intra4/intra16 based on SSE (~tad slower).
+    // For method <= 1, we refine intra4 or intra16 (but don't re-examine mode).
+    DistoRefine(it, (method >= 2));
     SimpleQuantize(it, rd);
   }
   is_skipped = (rd->nz == 0);
@@ -925,6 +1189,3 @@ int VP8Decimate(VP8EncIterator* const it, VP8ModeScore* const rd, int rd_opt) {
   return is_skipped;
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/syntax.c b/drivers/webp/enc/syntax.c
index 4221436ff9..a0e79ef404 100644
--- a/drivers/webp/enc/syntax.c
+++ b/drivers/webp/enc/syntax.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Header syntax writing
@@ -11,35 +13,20 @@
 
 #include <assert.h>
 
-#include "../format_constants.h"
+#include "../utils/utils.h"
+#include "../webp/format_constants.h"  // RIFF constants
+#include "../webp/mux_types.h"         // ALPHA_FLAG
 #include "./vp8enci.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 //------------------------------------------------------------------------------
 // Helper functions
 
-// TODO(later): Move to webp/format_constants.h?
-static void PutLE24(uint8_t* const data, uint32_t val) {
-  data[0] = (val >>  0) & 0xff;
-  data[1] = (val >>  8) & 0xff;
-  data[2] = (val >> 16) & 0xff;
-}
-
-static void PutLE32(uint8_t* const data, uint32_t val) {
-  PutLE24(data, val);
-  data[3] = (val >> 24) & 0xff;
-}
-
 static int IsVP8XNeeded(const VP8Encoder* const enc) {
   return !!enc->has_alpha_;  // Currently the only case when VP8X is needed.
                              // This could change in the future.
 }
 
 static int PutPaddingByte(const WebPPicture* const pic) {
-
   const uint8_t pad_byte[1] = { 0 };
   return !!pic->writer(pad_byte, 1, pic);
 }
@@ -73,14 +60,14 @@ static WebPEncodingError PutVP8XHeader(const VP8Encoder* const enc) {
   assert(pic->width <= MAX_CANVAS_SIZE && pic->height <= MAX_CANVAS_SIZE);
 
   if (enc->has_alpha_) {
-    flags |= ALPHA_FLAG_BIT;
+    flags |= ALPHA_FLAG;
   }
 
   PutLE32(vp8x + TAG_SIZE,              VP8X_CHUNK_SIZE);
   PutLE32(vp8x + CHUNK_HEADER_SIZE,     flags);
   PutLE24(vp8x + CHUNK_HEADER_SIZE + 4, pic->width - 1);
   PutLE24(vp8x + CHUNK_HEADER_SIZE + 7, pic->height - 1);
-  if(!pic->writer(vp8x, sizeof(vp8x), pic)) {
+  if (!pic->writer(vp8x, sizeof(vp8x), pic)) {
     return VP8_ENC_ERROR_BAD_WRITE;
   }
   return VP8_ENC_OK;
@@ -199,8 +186,8 @@ static int PutWebPHeaders(const VP8Encoder* const enc, size_t size0,
 // Segmentation header
 static void PutSegmentHeader(VP8BitWriter* const bw,
                              const VP8Encoder* const enc) {
-  const VP8SegmentHeader* const hdr = &enc->segment_hdr_;
-  const VP8Proba* const proba = &enc->proba_;
+  const VP8EncSegmentHeader* const hdr = &enc->segment_hdr_;
+  const VP8EncProba* const proba = &enc->proba_;
   if (VP8PutBitUniform(bw, (hdr->num_segments_ > 1))) {
     // We always 'update' the quant and filter strength values
     const int update_data = 1;
@@ -210,16 +197,16 @@ static void PutSegmentHeader(VP8BitWriter* const bw,
       // we always use absolute values, not relative ones
       VP8PutBitUniform(bw, 1);   // (segment_feature_mode = 1. Paragraph 9.3.)
       for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
-        VP8PutSignedValue(bw, enc->dqm_[s].quant_, 7);
+        VP8PutSignedBits(bw, enc->dqm_[s].quant_, 7);
       }
       for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
-        VP8PutSignedValue(bw, enc->dqm_[s].fstrength_, 6);
+        VP8PutSignedBits(bw, enc->dqm_[s].fstrength_, 6);
       }
     }
     if (hdr->update_map_) {
       for (s = 0; s < 3; ++s) {
         if (VP8PutBitUniform(bw, (proba->segments_[s] != 255u))) {
-          VP8PutValue(bw, proba->segments_[s], 8);
+          VP8PutBits(bw, proba->segments_[s], 8);
         }
       }
     }
@@ -228,20 +215,20 @@ static void PutSegmentHeader(VP8BitWriter* const bw,
 
 // Filtering parameters header
 static void PutFilterHeader(VP8BitWriter* const bw,
-                            const VP8FilterHeader* const hdr) {
+                            const VP8EncFilterHeader* const hdr) {
   const int use_lf_delta = (hdr->i4x4_lf_delta_ != 0);
   VP8PutBitUniform(bw, hdr->simple_);
-  VP8PutValue(bw, hdr->level_, 6);
-  VP8PutValue(bw, hdr->sharpness_, 3);
+  VP8PutBits(bw, hdr->level_, 6);
+  VP8PutBits(bw, hdr->sharpness_, 3);
   if (VP8PutBitUniform(bw, use_lf_delta)) {
     // '0' is the default value for i4x4_lf_delta_ at frame #0.
     const int need_update = (hdr->i4x4_lf_delta_ != 0);
     if (VP8PutBitUniform(bw, need_update)) {
       // we don't use ref_lf_delta => emit four 0 bits
-      VP8PutValue(bw, 0, 4);
+      VP8PutBits(bw, 0, 4);
       // we use mode_lf_delta for i4x4
-      VP8PutSignedValue(bw, hdr->i4x4_lf_delta_, 6);
-      VP8PutValue(bw, 0, 3);    // all others unused
+      VP8PutSignedBits(bw, hdr->i4x4_lf_delta_, 6);
+      VP8PutBits(bw, 0, 3);    // all others unused
     }
   }
 }
@@ -249,12 +236,12 @@ static void PutFilterHeader(VP8BitWriter* const bw,
 // Nominal quantization parameters
 static void PutQuant(VP8BitWriter* const bw,
                      const VP8Encoder* const enc) {
-  VP8PutValue(bw, enc->base_quant_, 7);
-  VP8PutSignedValue(bw, enc->dq_y1_dc_, 4);
-  VP8PutSignedValue(bw, enc->dq_y2_dc_, 4);
-  VP8PutSignedValue(bw, enc->dq_y2_ac_, 4);
-  VP8PutSignedValue(bw, enc->dq_uv_dc_, 4);
-  VP8PutSignedValue(bw, enc->dq_uv_ac_, 4);
+  VP8PutBits(bw, enc->base_quant_, 7);
+  VP8PutSignedBits(bw, enc->dq_y1_dc_, 4);
+  VP8PutSignedBits(bw, enc->dq_y2_dc_, 4);
+  VP8PutSignedBits(bw, enc->dq_y2_ac_, 4);
+  VP8PutSignedBits(bw, enc->dq_uv_dc_, 4);
+  VP8PutSignedBits(bw, enc->dq_uv_ac_, 4);
 }
 
 // Partition sizes
@@ -276,58 +263,23 @@ static int EmitPartitionsSize(const VP8Encoder* const enc,
 
 //------------------------------------------------------------------------------
 
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-
-#define KTRAILER_SIZE 8
-
-static int WriteExtensions(VP8Encoder* const enc) {
-  uint8_t buffer[KTRAILER_SIZE];
-  VP8BitWriter* const bw = &enc->bw_;
-  WebPPicture* const pic = enc->pic_;
-
-  // Layer (bytes 0..3)
-  PutLE24(buffer + 0, enc->layer_data_size_);
-  buffer[3] = enc->pic_->colorspace & WEBP_CSP_UV_MASK;
-  if (enc->layer_data_size_ > 0) {
-    assert(enc->use_layer_);
-    // append layer data to last partition
-    if (!VP8BitWriterAppend(&enc->parts_[enc->num_parts_ - 1],
-                            enc->layer_data_, enc->layer_data_size_)) {
-      return WebPEncodingSetError(pic, VP8_ENC_ERROR_BITSTREAM_OUT_OF_MEMORY);
-    }
-  }
-
-  buffer[KTRAILER_SIZE - 1] = 0x01;  // marker
-  if (!VP8BitWriterAppend(bw, buffer, KTRAILER_SIZE)) {
-    return WebPEncodingSetError(pic, VP8_ENC_ERROR_BITSTREAM_OUT_OF_MEMORY);
-  }
-  return 1;
-}
-
-#endif    /* WEBP_EXPERIMENTAL_FEATURES */
-
-//------------------------------------------------------------------------------
-
-static size_t GeneratePartition0(VP8Encoder* const enc) {
+static int GeneratePartition0(VP8Encoder* const enc) {
   VP8BitWriter* const bw = &enc->bw_;
   const int mb_size = enc->mb_w_ * enc->mb_h_;
   uint64_t pos1, pos2, pos3;
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-  const int need_extensions = enc->use_layer_;
-#endif
 
   pos1 = VP8BitWriterPos(bw);
-  VP8BitWriterInit(bw, mb_size * 7 / 8);        // ~7 bits per macroblock
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-  VP8PutBitUniform(bw, need_extensions);   // extensions
-#else
+  if (!VP8BitWriterInit(bw, mb_size * 7 / 8)) {        // ~7 bits per macroblock
+    return WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
+  }
   VP8PutBitUniform(bw, 0);   // colorspace
-#endif
   VP8PutBitUniform(bw, 0);   // clamp type
 
   PutSegmentHeader(bw, enc);
   PutFilterHeader(bw, &enc->filter_hdr_);
-  VP8PutValue(bw, enc->config_->partitions, 2);
+  VP8PutBits(bw, enc->num_parts_ == 8 ? 3 :
+                 enc->num_parts_ == 4 ? 2 :
+                 enc->num_parts_ == 2 ? 1 : 0, 2);
   PutQuant(bw, enc);
   VP8PutBitUniform(bw, 0);   // no proba update
   VP8WriteProbas(bw, &enc->proba_);
@@ -335,21 +287,17 @@ static size_t GeneratePartition0(VP8Encoder* const enc) {
   VP8CodeIntraModes(enc);
   VP8BitWriterFinish(bw);
 
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-  if (need_extensions && !WriteExtensions(enc)) {
-    return 0;
-  }
-#endif
-
   pos3 = VP8BitWriterPos(bw);
 
   if (enc->pic_->stats) {
     enc->pic_->stats->header_bytes[0] = (int)((pos2 - pos1 + 7) >> 3);
     enc->pic_->stats->header_bytes[1] = (int)((pos3 - pos2 + 7) >> 3);
     enc->pic_->stats->alpha_data_size = (int)enc->alpha_data_size_;
-    enc->pic_->stats->layer_data_size = (int)enc->layer_data_size_;
   }
-  return !bw->error_;
+  if (bw->error_) {
+    return WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
+  }
+  return 1;
 }
 
 void VP8EncFreeBitWriters(VP8Encoder* const enc) {
@@ -371,7 +319,8 @@ int VP8EncWrite(VP8Encoder* const enc) {
   int p;
 
   // Partition #0 with header and partition sizes
-  ok = !!GeneratePartition0(enc);
+  ok = GeneratePartition0(enc);
+  if (!ok) return 0;
 
   // Compute VP8 size
   vp8_size = VP8_FRAME_HEADER_SIZE +
@@ -432,6 +381,3 @@ int VP8EncWrite(VP8Encoder* const enc) {
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/tree.c b/drivers/webp/enc/tree.c
index 8b25e5e488..f141006d19 100644
--- a/drivers/webp/enc/tree.c
+++ b/drivers/webp/enc/tree.c
@@ -1,27 +1,24 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
-// Token probabilities
+// Coding of token probabilities, intra modes and segments.
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
 #include "./vp8enci.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 //------------------------------------------------------------------------------
 // Default probabilities
 
 // Paragraph 13.5
 const uint8_t
   VP8CoeffsProba0[NUM_TYPES][NUM_BANDS][NUM_CTX][NUM_PROBAS] = {
-  // genereated using vp8_default_coef_probs() in entropy.c:129
   { { { 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128 },
       { 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128 },
       { 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128 }
@@ -157,7 +154,7 @@ const uint8_t
 };
 
 void VP8DefaultProbas(VP8Encoder* const enc) {
-  VP8Proba* const probas = &enc->proba_;
+  VP8EncProba* const probas = &enc->proba_;
   probas->use_skip_proba_ = 0;
   memset(probas->segments_, 255u, sizeof(probas->segments_));
   memcpy(probas->coeffs_, VP8CoeffsProba0, sizeof(VP8CoeffsProba0));
@@ -318,7 +315,7 @@ void VP8CodeIntraModes(VP8Encoder* const enc) {
   VP8EncIterator it;
   VP8IteratorInit(enc, &it);
   do {
-    const VP8MBInfo* mb = it.mb_;
+    const VP8MBInfo* const mb = it.mb_;
     const uint8_t* preds = it.preds_;
     if (enc->segment_hdr_.update_map_) {
       PutSegment(bw, mb->segment_, enc->proba_.segments_);
@@ -343,7 +340,7 @@ void VP8CodeIntraModes(VP8Encoder* const enc) {
       }
     }
     PutUVMode(bw, mb->uv_mode_);
-  } while (VP8IteratorNext(&it, 0));
+  } while (VP8IteratorNext(&it));
 }
 
 //------------------------------------------------------------------------------
@@ -485,7 +482,7 @@ const uint8_t
   }
 };
 
-void VP8WriteProbas(VP8BitWriter* const bw, const VP8Proba* const probas) {
+void VP8WriteProbas(VP8BitWriter* const bw, const VP8EncProba* const probas) {
   int t, b, c, p;
   for (t = 0; t < NUM_TYPES; ++t) {
     for (b = 0; b < NUM_BANDS; ++b) {
@@ -494,17 +491,14 @@ void VP8WriteProbas(VP8BitWriter* const bw, const VP8Proba* const probas) {
           const uint8_t p0 = probas->coeffs_[t][b][c][p];
           const int update = (p0 != VP8CoeffsProba0[t][b][c][p]);
           if (VP8PutBit(bw, update, VP8CoeffsUpdateProba[t][b][c][p])) {
-            VP8PutValue(bw, p0, 8);
+            VP8PutBits(bw, p0, 8);
           }
         }
       }
     }
   }
   if (VP8PutBitUniform(bw, probas->use_skip_proba_)) {
-    VP8PutValue(bw, probas->skip_proba_, 8);
+    VP8PutBits(bw, probas->skip_proba_, 8);
   }
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/vp8enci.h b/drivers/webp/enc/vp8enci.h
index 936e1c18ce..1a7ebe5703 100644
--- a/drivers/webp/enc/vp8enci.h
+++ b/drivers/webp/enc/vp8enci.h
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 //   WebP encoder: internal header.
@@ -13,11 +15,18 @@
 #define WEBP_ENC_VP8ENCI_H_
 
 #include <string.h>     // for memcpy()
-#include "../encode.h"
+#include "../dec/common.h"
 #include "../dsp/dsp.h"
 #include "../utils/bit_writer.h"
+#include "../utils/thread.h"
+#include "../utils/utils.h"
+#include "../webp/encode.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+#include "./vp8li.h"
+#endif  // WEBP_EXPERIMENTAL_FEATURES
+
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -26,141 +35,94 @@ extern "C" {
 
 // version numbers
 #define ENC_MAJ_VERSION 0
-#define ENC_MIN_VERSION 2
-#define ENC_REV_VERSION 0
-
-// size of histogram used by CollectHistogram.
-#define MAX_COEFF_THRESH   64
-
-// intra prediction modes
-enum { B_DC_PRED = 0,   // 4x4 modes
-       B_TM_PRED = 1,
-       B_VE_PRED = 2,
-       B_HE_PRED = 3,
-       B_RD_PRED = 4,
-       B_VR_PRED = 5,
-       B_LD_PRED = 6,
-       B_VL_PRED = 7,
-       B_HD_PRED = 8,
-       B_HU_PRED = 9,
-       NUM_BMODES = B_HU_PRED + 1 - B_DC_PRED,  // = 10
-
-       // Luma16 or UV modes
-       DC_PRED = B_DC_PRED, V_PRED = B_VE_PRED,
-       H_PRED = B_HE_PRED, TM_PRED = B_TM_PRED
-     };
+#define ENC_MIN_VERSION 4
+#define ENC_REV_VERSION 4
 
-enum { NUM_MB_SEGMENTS = 4,
-       MAX_NUM_PARTITIONS = 8,
-       NUM_TYPES = 4,   // 0: i16-AC,  1: i16-DC,  2:chroma-AC,  3:i4-AC
-       NUM_BANDS = 8,
-       NUM_CTX = 3,
-       NUM_PROBAS = 11,
-       MAX_LF_LEVELS = 64,      // Maximum loop filter level
-       MAX_VARIABLE_LEVEL = 67  // last (inclusive) level with variable cost
+enum { MAX_LF_LEVELS = 64,       // Maximum loop filter level
+       MAX_VARIABLE_LEVEL = 67,  // last (inclusive) level with variable cost
+       MAX_LEVEL = 2047          // max level (note: max codable is 2047 + 67)
      };
 
-// YUV-cache parameters. Cache is 16-pixels wide.
-// The original or reconstructed samples can be accessed using VP8Scan[]
+typedef enum {   // Rate-distortion optimization levels
+  RD_OPT_NONE        = 0,  // no rd-opt
+  RD_OPT_BASIC       = 1,  // basic scoring (no trellis)
+  RD_OPT_TRELLIS     = 2,  // perform trellis-quant on the final decision only
+  RD_OPT_TRELLIS_ALL = 3   // trellis-quant for every scoring (much slower)
+} VP8RDLevel;
+
+// YUV-cache parameters. Cache is 32-bytes wide (= one cacheline).
+// The original or reconstructed samples can be accessed using VP8Scan[].
 // The predicted blocks can be accessed using offsets to yuv_p_ and
-// the arrays VP8*ModeOffsets[];
-//         +----+      YUV Samples area. See VP8Scan[] for accessing the blocks.
-//  Y_OFF  |YYYY| <- original samples  (enc->yuv_in_)
-//         |YYYY|
-//         |YYYY|
-//         |YYYY|
-//  U_OFF  |UUVV| V_OFF  (=U_OFF + 8)
-//         |UUVV|
-//         +----+
-//  Y_OFF  |YYYY| <- compressed/decoded samples  ('yuv_out_')
-//         |YYYY|    There are two buffers like this ('yuv_out_'/'yuv_out2_')
-//         |YYYY|
-//         |YYYY|
-//  U_OFF  |UUVV| V_OFF
-//         |UUVV|
-//          x2 (for yuv_out2_)
-//         +----+     Prediction area ('yuv_p_', size = PRED_SIZE)
-// I16DC16 |YYYY|  Intra16 predictions (16x16 block each)
-//         |YYYY|
-//         |YYYY|
-//         |YYYY|
-// I16TM16 |YYYY|
-//         |YYYY|
-//         |YYYY|
-//         |YYYY|
-// I16VE16 |YYYY|
-//         |YYYY|
-//         |YYYY|
-//         |YYYY|
-// I16HE16 |YYYY|
-//         |YYYY|
-//         |YYYY|
-//         |YYYY|
-//         +----+  Chroma U/V predictions (16x8 block each)
-// C8DC8   |UUVV|
-//         |UUVV|
-// C8TM8   |UUVV|
-//         |UUVV|
-// C8VE8   |UUVV|
-//         |UUVV|
-// C8HE8   |UUVV|
-//         |UUVV|
-//         +----+  Intra 4x4 predictions (4x4 block each)
-//         |YYYY| I4DC4 I4TM4 I4VE4 I4HE4
-//         |YYYY| I4RD4 I4VR4 I4LD4 I4VL4
-//         |YY..| I4HD4 I4HU4 I4TMP
-//         +----+
-#define BPS       16   // this is the common stride
-#define Y_SIZE   (BPS * 16)
-#define UV_SIZE  (BPS * 8)
-#define YUV_SIZE (Y_SIZE + UV_SIZE)
-#define PRED_SIZE (6 * 16 * BPS + 12 * BPS)
-#define Y_OFF    (0)
-#define U_OFF    (Y_SIZE)
-#define V_OFF    (U_OFF + 8)
-#define ALIGN_CST 15
-#define DO_ALIGN(PTR) ((uintptr_t)((PTR) + ALIGN_CST) & ~ALIGN_CST)
-
-extern const int VP8Scan[16 + 4 + 4];           // in quant.c
-extern const int VP8UVModeOffsets[4];           // in analyze.c
+// the arrays VP8*ModeOffsets[].
+// * YUV Samples area (yuv_in_/yuv_out_/yuv_out2_)
+//   (see VP8Scan[] for accessing the blocks, along with
+//   Y_OFF_ENC/U_OFF_ENC/V_OFF_ENC):
+//             +----+----+
+//  Y_OFF_ENC  |YYYY|UUVV|
+//  U_OFF_ENC  |YYYY|UUVV|
+//  V_OFF_ENC  |YYYY|....| <- 25% wasted U/V area
+//             |YYYY|....|
+//             +----+----+
+// * Prediction area ('yuv_p_', size = PRED_SIZE_ENC)
+//   Intra16 predictions (16x16 block each, two per row):
+//         |I16DC16|I16TM16|
+//         |I16VE16|I16HE16|
+//   Chroma U/V predictions (16x8 block each, two per row):
+//         |C8DC8|C8TM8|
+//         |C8VE8|C8HE8|
+//   Intra 4x4 predictions (4x4 block each)
+//         |I4DC4 I4TM4 I4VE4 I4HE4|I4RD4 I4VR4 I4LD4 I4VL4|
+//         |I4HD4 I4HU4 I4TMP .....|.......................| <- ~31% wasted
+#define YUV_SIZE_ENC (BPS * 16)
+#define PRED_SIZE_ENC (32 * BPS + 16 * BPS + 8 * BPS)   // I16+Chroma+I4 preds
+#define Y_OFF_ENC    (0)
+#define U_OFF_ENC    (16)
+#define V_OFF_ENC    (16 + 8)
+
+extern const int VP8Scan[16];           // in quant.c
+extern const int VP8UVModeOffsets[4];   // in analyze.c
 extern const int VP8I16ModeOffsets[4];
 extern const int VP8I4ModeOffsets[NUM_BMODES];
 
 // Layout of prediction blocks
 // intra 16x16
 #define I16DC16 (0 * 16 * BPS)
-#define I16TM16 (1 * 16 * BPS)
-#define I16VE16 (2 * 16 * BPS)
-#define I16HE16 (3 * 16 * BPS)
+#define I16TM16 (I16DC16 + 16)
+#define I16VE16 (1 * 16 * BPS)
+#define I16HE16 (I16VE16 + 16)
 // chroma 8x8, two U/V blocks side by side (hence: 16x8 each)
-#define C8DC8 (4 * 16 * BPS)
-#define C8TM8 (4 * 16 * BPS + 8 * BPS)
-#define C8VE8 (5 * 16 * BPS)
-#define C8HE8 (5 * 16 * BPS + 8 * BPS)
+#define C8DC8 (2 * 16 * BPS)
+#define C8TM8 (C8DC8 + 1 * 16)
+#define C8VE8 (2 * 16 * BPS + 8 * BPS)
+#define C8HE8 (C8VE8 + 1 * 16)
 // intra 4x4
-#define I4DC4 (6 * 16 * BPS +  0)
-#define I4TM4 (6 * 16 * BPS +  4)
-#define I4VE4 (6 * 16 * BPS +  8)
-#define I4HE4 (6 * 16 * BPS + 12)
-#define I4RD4 (6 * 16 * BPS + 4 * BPS +  0)
-#define I4VR4 (6 * 16 * BPS + 4 * BPS +  4)
-#define I4LD4 (6 * 16 * BPS + 4 * BPS +  8)
-#define I4VL4 (6 * 16 * BPS + 4 * BPS + 12)
-#define I4HD4 (6 * 16 * BPS + 8 * BPS +  0)
-#define I4HU4 (6 * 16 * BPS + 8 * BPS +  4)
-#define I4TMP (6 * 16 * BPS + 8 * BPS +  8)
+#define I4DC4 (3 * 16 * BPS +  0)
+#define I4TM4 (I4DC4 +  4)
+#define I4VE4 (I4DC4 +  8)
+#define I4HE4 (I4DC4 + 12)
+#define I4RD4 (I4DC4 + 16)
+#define I4VR4 (I4DC4 + 20)
+#define I4LD4 (I4DC4 + 24)
+#define I4VL4 (I4DC4 + 28)
+#define I4HD4 (3 * 16 * BPS + 4 * BPS)
+#define I4HU4 (I4HD4 + 4)
+#define I4TMP (I4HD4 + 8)
 
 typedef int64_t score_t;     // type used for scores, rate, distortion
+// Note that MAX_COST is not the maximum allowed by sizeof(score_t),
+// in order to allow overflowing computations.
 #define MAX_COST ((score_t)0x7fffffffffffffLL)
 
 #define QFIX 17
 #define BIAS(b)  ((b) << (QFIX - 8))
 // Fun fact: this is the _only_ line where we're actually being lossy and
 // discarding bits.
-static WEBP_INLINE int QUANTDIV(int n, int iQ, int B) {
-  return (n * iQ + B) >> QFIX;
+static WEBP_INLINE int QUANTDIV(uint32_t n, uint32_t iQ, uint32_t B) {
+  return (int)((n * iQ + B) >> QFIX);
 }
-extern const uint8_t VP8Zigzag[16];
+
+// Uncomment the following to remove token-buffer code:
+// #define DISABLE_TOKEN_BUFFER
 
 //------------------------------------------------------------------------------
 // Headers
@@ -169,6 +131,8 @@ typedef uint32_t proba_t;   // 16b + 16b
 typedef uint8_t ProbaArray[NUM_CTX][NUM_PROBAS];
 typedef proba_t StatsArray[NUM_CTX][NUM_PROBAS];
 typedef uint16_t CostArray[NUM_CTX][MAX_VARIABLE_LEVEL + 1];
+typedef const uint16_t* (*CostArrayPtr)[NUM_CTX];   // for easy casting
+typedef const uint16_t* CostArrayMap[16][NUM_CTX];
 typedef double LFStats[NUM_MB_SEGMENTS][MAX_LF_LEVELS];  // filter stats
 
 typedef struct VP8Encoder VP8Encoder;
@@ -179,19 +143,20 @@ typedef struct {
   int update_map_;        // whether to update the segment map or not.
                           // must be 0 if there's only 1 segment.
   int size_;              // bit-cost for transmitting the segment map
-} VP8SegmentHeader;
+} VP8EncSegmentHeader;
 
 // Struct collecting all frame-persistent probabilities.
 typedef struct {
   uint8_t segments_[3];     // probabilities for segment tree
   uint8_t skip_proba_;      // final probability of being skipped.
-  ProbaArray coeffs_[NUM_TYPES][NUM_BANDS];      // 924 bytes
+  ProbaArray coeffs_[NUM_TYPES][NUM_BANDS];      // 1056 bytes
   StatsArray stats_[NUM_TYPES][NUM_BANDS];       // 4224 bytes
-  CostArray level_cost_[NUM_TYPES][NUM_BANDS];   // 11.4k
+  CostArray level_cost_[NUM_TYPES][NUM_BANDS];   // 13056 bytes
+  CostArrayMap remapped_costs_[NUM_TYPES];       // 1536 bytes
   int dirty_;               // if true, need to call VP8CalculateLevelCosts()
   int use_skip_proba_;      // Note: we always use skip_proba for now.
   int nb_skip_;             // number of skipped blocks
-} VP8Proba;
+} VP8EncProba;
 
 // Filter parameters. Not actually used in the code (we don't perform
 // the in-loop filtering), but filled from user's config
@@ -200,7 +165,7 @@ typedef struct {
   int level_;              // base filter level [0..63]
   int sharpness_;          // [0..7]
   int i4x4_lf_delta_;      // delta filter level for i4x4 relative to i16x16
-} VP8FilterHeader;
+} VP8EncFilterHeader;
 
 //------------------------------------------------------------------------------
 // Informations about the macroblocks.
@@ -217,8 +182,8 @@ typedef struct {
 typedef struct VP8Matrix {
   uint16_t q_[16];        // quantizer steps
   uint16_t iq_[16];       // reciprocals, fixed point.
-  uint16_t bias_[16];     // rounding bias
-  uint16_t zthresh_[16];  // value under which a coefficient is zeroed
+  uint32_t bias_[16];     // rounding bias
+  uint32_t zthresh_[16];  // value below which a coefficient is zeroed
   uint16_t sharpen_[16];  // frequency boosters for slight sharpening
 } VP8Matrix;
 
@@ -229,16 +194,19 @@ typedef struct {
   int beta_;       // filter-susceptibility, range [0,255].
   int quant_;      // final segment quantizer.
   int fstrength_;  // final in-loop filtering strength
+  int max_edge_;   // max edge delta (for filtering strength)
+  int min_disto_;  // minimum distortion required to trigger filtering record
   // reactivities
   int lambda_i16_, lambda_i4_, lambda_uv_;
   int lambda_mode_, lambda_trellis_, tlambda_;
   int lambda_trellis_i16_, lambda_trellis_i4_, lambda_trellis_uv_;
 } VP8SegmentInfo;
 
-// Handy transcient struct to accumulate score and info during RD-optimization
+// Handy transient struct to accumulate score and info during RD-optimization
 // and mode evaluation.
 typedef struct {
-  score_t D, SD, R, score;    // Distortion, spectral distortion, rate, score.
+  score_t D, SD;              // Distortion, spectral distortion
+  score_t H, R, score;        // header bits, rate, score.
   int16_t y_dc_levels[16];    // Quantized levels for luma-DC, luma-AC, chroma.
   int16_t y_ac_levels[16][16];
   int16_t uv_levels[4 + 4][16];
@@ -252,12 +220,11 @@ typedef struct {
 // right neighbouring data (samples, predictions, contexts, ...)
 typedef struct {
   int x_, y_;                      // current macroblock
-  int y_offset_, uv_offset_;       // offset to the luma / chroma planes
   int y_stride_, uv_stride_;       // respective strides
-  uint8_t*      yuv_in_;           // borrowed from enc_ (for now)
-  uint8_t*      yuv_out_;          // ''
-  uint8_t*      yuv_out2_;         // ''
-  uint8_t*      yuv_p_;            // ''
+  uint8_t*      yuv_in_;           // input samples
+  uint8_t*      yuv_out_;          // output samples
+  uint8_t*      yuv_out2_;         // secondary buffer swapped with yuv_out_.
+  uint8_t*      yuv_p_;            // scratch buffer for prediction
   VP8Encoder*   enc_;              // back-pointer
   VP8MBInfo*    mb_;               // current macroblock
   VP8BitWriter* bw_;               // current bit-writer
@@ -273,24 +240,44 @@ typedef struct {
   uint64_t      uv_bits_;          // macroblock bit-cost for chroma
   LFStats*      lf_stats_;         // filter stats (borrowed from enc_)
   int           do_trellis_;       // if true, perform extra level optimisation
-  int           done_;             // true when scan is finished
+  int           count_down_;       // number of mb still to be processed
+  int           count_down0_;      // starting counter value (for progress)
   int           percent0_;         // saved initial progress percent
+
+  uint8_t* y_left_;    // left luma samples (addressable from index -1 to 15).
+  uint8_t* u_left_;    // left u samples (addressable from index -1 to 7)
+  uint8_t* v_left_;    // left v samples (addressable from index -1 to 7)
+
+  uint8_t* y_top_;     // top luma samples at position 'x_'
+  uint8_t* uv_top_;    // top u/v samples at position 'x_', packed as 16 bytes
+
+  // memory for storing y/u/v_left_
+  uint8_t yuv_left_mem_[17 + 16 + 16 + 8 + WEBP_ALIGN_CST];
+  // memory for yuv_*
+  uint8_t yuv_mem_[3 * YUV_SIZE_ENC + PRED_SIZE_ENC + WEBP_ALIGN_CST];
 } VP8EncIterator;
 
   // in iterator.c
-// must be called first.
+// must be called first
 void VP8IteratorInit(VP8Encoder* const enc, VP8EncIterator* const it);
-// restart a scan.
+// restart a scan
 void VP8IteratorReset(VP8EncIterator* const it);
-// import samples from source
-void VP8IteratorImport(const VP8EncIterator* const it);
+// reset iterator position to row 'y'
+void VP8IteratorSetRow(VP8EncIterator* const it, int y);
+// set count down (=number of iterations to go)
+void VP8IteratorSetCountDown(VP8EncIterator* const it, int count_down);
+// return true if iteration is finished
+int VP8IteratorIsDone(const VP8EncIterator* const it);
+// Import uncompressed samples from source.
+// If tmp_32 is not NULL, import boundary samples too.
+// tmp_32 is a 32-bytes scratch buffer that must be aligned in memory.
+void VP8IteratorImport(VP8EncIterator* const it, uint8_t* tmp_32);
 // export decimated samples
 void VP8IteratorExport(const VP8EncIterator* const it);
-// go to next macroblock. Returns !done_. If *block_to_save is non-null, will
-// save the boundary values to top_/left_ arrays. block_to_save can be
-// it->yuv_out_ or it->yuv_in_.
-int VP8IteratorNext(VP8EncIterator* const it,
-                    const uint8_t* const block_to_save);
+// go to next macroblock. Returns false if not finished.
+int VP8IteratorNext(VP8EncIterator* const it);
+// save the yuv_out_ boundary values to top_/left_ arrays for next iterations.
+void VP8IteratorSaveBoundary(VP8EncIterator* const it);
 // Report progression based on macroblock rows. Return 0 for user-abort request.
 int VP8IteratorProgress(const VP8EncIterator* const it,
                         int final_delta_percent);
@@ -314,44 +301,43 @@ void VP8SetSegment(const VP8EncIterator* const it, int segment);
 //------------------------------------------------------------------------------
 // Paginated token buffer
 
-// WIP: #define USE_TOKEN_BUFFER
+typedef struct VP8Tokens VP8Tokens;  // struct details in token.c
 
-#ifdef USE_TOKEN_BUFFER
+typedef struct {
+#if !defined(DISABLE_TOKEN_BUFFER)
+  VP8Tokens* pages_;        // first page
+  VP8Tokens** last_page_;   // last page
+  uint16_t* tokens_;        // set to (*last_page_)->tokens_
+  int left_;                // how many free tokens left before the page is full
+  int page_size_;           // number of tokens per page
+#endif
+  int error_;         // true in case of malloc error
+} VP8TBuffer;
 
-#define MAX_NUM_TOKEN 2048
+// initialize an empty buffer
+void VP8TBufferInit(VP8TBuffer* const b, int page_size);
+void VP8TBufferClear(VP8TBuffer* const b);   // de-allocate pages memory
 
-typedef struct VP8Tokens VP8Tokens;
-struct VP8Tokens {
-  uint16_t tokens_[MAX_NUM_TOKEN];  // bit#15: bit, bits 0..14: slot
-  int left_;
-  VP8Tokens* next_;
-};
+#if !defined(DISABLE_TOKEN_BUFFER)
 
-typedef struct {
-  VP8Tokens* rows_;
-  uint16_t* tokens_;    // set to (*last_)->tokens_
-  VP8Tokens** last_;
-  int left_;
-  int error_;  // true in case of malloc error
-} VP8TBuffer;
+// Finalizes bitstream when probabilities are known.
+// Deletes the allocated token memory if final_pass is true.
+int VP8EmitTokens(VP8TBuffer* const b, VP8BitWriter* const bw,
+                  const uint8_t* const probas, int final_pass);
 
-void VP8TBufferInit(VP8TBuffer* const b);    // initialize an empty buffer
-int VP8TBufferNewPage(VP8TBuffer* const b);  // allocate a new page
-void VP8TBufferClear(VP8TBuffer* const b);   // de-allocate memory
+// record the coding of coefficients without knowing the probabilities yet
+int VP8RecordCoeffTokens(const int ctx, const int coeff_type,
+                         int first, int last,
+                         const int16_t* const coeffs,
+                         VP8TBuffer* const tokens);
 
-int VP8EmitTokens(const VP8TBuffer* const b, VP8BitWriter* const bw,
-                  const uint8_t* const probas);
+// Estimate the final coded size given a set of 'probas'.
+size_t VP8EstimateTokenSize(VP8TBuffer* const b, const uint8_t* const probas);
 
-static WEBP_INLINE int VP8AddToken(VP8TBuffer* const b,
-                                   int bit, int proba_idx) {
-  if (b->left_ > 0 || VP8TBufferNewPage(b)) {
-    const int slot = --b->left_;
-    b->tokens_[slot] = (bit << 15) | proba_idx;
-  }
-  return bit;
-}
+// unused for now
+void VP8TokenToStats(const VP8TBuffer* const b, proba_t* const stats);
 
-#endif  // USE_TOKEN_BUFFER
+#endif  // !DISABLE_TOKEN_BUFFER
 
 //------------------------------------------------------------------------------
 // VP8Encoder
@@ -361,8 +347,8 @@ struct VP8Encoder {
   WebPPicture* pic_;            // input / output picture
 
   // headers
-  VP8FilterHeader   filter_hdr_;     // filtering information
-  VP8SegmentHeader  segment_hdr_;    // segment information
+  VP8EncFilterHeader   filter_hdr_;     // filtering information
+  VP8EncSegmentHeader  segment_hdr_;    // segment information
 
   int profile_;                      // VP8's profile, deduced from Config.
 
@@ -376,6 +362,7 @@ struct VP8Encoder {
   // per-partition boolean decoders.
   VP8BitWriter bw_;                         // part0
   VP8BitWriter parts_[MAX_NUM_PARTITIONS];  // token partitions
+  VP8TBuffer tokens_;                       // token buffer
 
   int percent_;                             // for progress
 
@@ -383,17 +370,13 @@ struct VP8Encoder {
   int has_alpha_;
   uint8_t* alpha_data_;       // non-NULL if transparency is present
   uint32_t alpha_data_size_;
-
-  // enhancement layer
-  int use_layer_;
-  VP8BitWriter layer_bw_;
-  uint8_t* layer_data_;
-  size_t layer_data_size_;
+  WebPWorker alpha_worker_;
 
   // quantization info (one set of DC/AC dequant factor per segment)
   VP8SegmentInfo dqm_[NUM_MB_SEGMENTS];
   int base_quant_;                 // nominal quantizer value. Only used
                                    // for relative coding of segments' quant.
+  int alpha_;                      // global susceptibility (<=> complexity)
   int uv_alpha_;                   // U/V quantization susceptibility
   // global offset of quantizers, shared by all segments
   int dq_y1_dc_;
@@ -401,34 +384,29 @@ struct VP8Encoder {
   int dq_uv_dc_, dq_uv_ac_;
 
   // probabilities and statistics
-  VP8Proba proba_;
-  uint64_t sse_[4];        // sum of Y/U/V/A squared errors for all macroblocks
-  uint64_t sse_count_;     // pixel count for the sse_[] stats
-  int      coded_size_;
-  int      residual_bytes_[3][4];
-  int      block_count_[3];
+  VP8EncProba proba_;
+  uint64_t    sse_[4];      // sum of Y/U/V/A squared errors for all macroblocks
+  uint64_t    sse_count_;   // pixel count for the sse_[] stats
+  int         coded_size_;
+  int         residual_bytes_[3][4];
+  int         block_count_[3];
 
   // quality/speed settings
-  int method_;              // 0=fastest, 6=best/slowest.
-  int rd_opt_level_;        // Deduced from method_.
-  int max_i4_header_bits_;  // partition #0 safeness factor
+  int method_;               // 0=fastest, 6=best/slowest.
+  VP8RDLevel rd_opt_level_;  // Deduced from method_.
+  int max_i4_header_bits_;   // partition #0 safeness factor
+  int thread_level_;         // derived from config->thread_level
+  int do_search_;            // derived from config->target_XXX
+  int use_tokens_;           // if true, use token buffer
 
   // Memory
   VP8MBInfo* mb_info_;   // contextual macroblock infos (mb_w_ + 1)
   uint8_t*   preds_;     // predictions modes: (4*mb_w+1) * (4*mb_h+1)
   uint32_t*  nz_;        // non-zero bit context: mb_w+1
-  uint8_t*   yuv_in_;    // input samples
-  uint8_t*   yuv_out_;   // output samples
-  uint8_t*   yuv_out2_;  // secondary scratch out-buffer. swapped with yuv_out_.
-  uint8_t*   yuv_p_;     // scratch buffer for prediction
-  uint8_t   *y_top_;     // top luma samples.
-  uint8_t   *uv_top_;    // top u/v samples.
-                         // U and V are packed into 16 pixels (8 U + 8 V)
-  uint8_t   *y_left_;    // left luma samples (adressable from index -1 to 15).
-  uint8_t   *u_left_;    // left u samples (adressable from index -1 to 7)
-  uint8_t   *v_left_;    // left v samples (adressable from index -1 to 7)
-
-  LFStats   *lf_stats_;  // autofilter stats (if NULL, autofilter is off)
+  uint8_t*   y_top_;     // top luma samples.
+  uint8_t*   uv_top_;    // top u/v samples.
+                         // U and V are packed into 16 bytes (8 U + 8 V)
+  LFStats*   lf_stats_;  // autofilter stats (if NULL, autofilter is off)
 };
 
 //------------------------------------------------------------------------------
@@ -441,7 +419,7 @@ extern const uint8_t
 // Reset the token probabilities to their initial (default) values
 void VP8DefaultProbas(VP8Encoder* const enc);
 // Write the token probabilities
-void VP8WriteProbas(VP8BitWriter* const bw, const VP8Proba* const probas);
+void VP8WriteProbas(VP8BitWriter* const bw, const VP8EncProba* const probas);
 // Writes the partition #0 modes (that is: all intra modes)
 void VP8CodeIntraModes(VP8Encoder* const enc);
 
@@ -454,7 +432,11 @@ int VP8EncWrite(VP8Encoder* const enc);
 void VP8EncFreeBitWriters(VP8Encoder* const enc);
 
   // in frame.c
-extern const uint8_t VP8EncBands[16 + 1];
+extern const uint8_t VP8Cat3[];
+extern const uint8_t VP8Cat4[];
+extern const uint8_t VP8Cat5[];
+extern const uint8_t VP8Cat6[];
+
 // Form all the four Intra16x16 predictions in the yuv_p_ cache
 void VP8MakeLuma16Preds(const VP8EncIterator* const it);
 // Form all the four Chroma8x8 predictions in the yuv_p_ cache
@@ -466,9 +448,9 @@ void VP8MakeIntra4Preds(const VP8EncIterator* const it);
 int VP8GetCostLuma16(VP8EncIterator* const it, const VP8ModeScore* const rd);
 int VP8GetCostLuma4(VP8EncIterator* const it, const int16_t levels[16]);
 int VP8GetCostUV(VP8EncIterator* const it, const VP8ModeScore* const rd);
-// Main stat / coding passes
+// Main coding calls
 int VP8EncLoop(VP8Encoder* const enc);
-int VP8StatLoop(VP8Encoder* const enc);
+int VP8EncTokenLoop(VP8Encoder* const enc);
 
   // in webpenc.c
 // Assign an error code to a picture. Return false for convenience.
@@ -485,18 +467,14 @@ int VP8EncAnalyze(VP8Encoder* const enc);
 // Sets up segment's quantization values, base_quant_ and filter strengths.
 void VP8SetSegmentParams(VP8Encoder* const enc, float quality);
 // Pick best modes and fills the levels. Returns true if skipped.
-int VP8Decimate(VP8EncIterator* const it, VP8ModeScore* const rd, int rd_opt);
+int VP8Decimate(VP8EncIterator* const it, VP8ModeScore* const rd,
+                VP8RDLevel rd_opt);
 
   // in alpha.c
 void VP8EncInitAlpha(VP8Encoder* const enc);    // initialize alpha compression
+int VP8EncStartAlpha(VP8Encoder* const enc);    // start alpha coding process
 int VP8EncFinishAlpha(VP8Encoder* const enc);   // finalize compressed data
-void VP8EncDeleteAlpha(VP8Encoder* const enc);  // delete compressed data
-
-  // in layer.c
-void VP8EncInitLayer(VP8Encoder* const enc);     // init everything
-void VP8EncCodeLayerBlock(VP8EncIterator* it);   // code one more macroblock
-int VP8EncFinishLayer(VP8Encoder* const enc);    // finalize coding
-void VP8EncDeleteLayer(VP8Encoder* enc);         // reclaim memory
+int VP8EncDeleteAlpha(VP8Encoder* const enc);   // delete compressed data
 
   // in filter.c
 
@@ -516,9 +494,38 @@ void VP8InitFilter(VP8EncIterator* const it);
 void VP8StoreFilterStats(VP8EncIterator* const it);
 void VP8AdjustFilterStrength(VP8EncIterator* const it);
 
+// returns the approximate filtering strength needed to smooth a edge
+// step of 'delta', given a sharpness parameter 'sharpness'.
+int VP8FilterStrengthFromDelta(int sharpness, int delta);
+
+  // misc utils for picture_*.c:
+
+// Remove reference to the ARGB/YUVA buffer (doesn't free anything).
+void WebPPictureResetBuffers(WebPPicture* const picture);
+
+// Allocates ARGB buffer of given dimension (previous one is always free'd).
+// Preserves the YUV(A) buffer. Returns false in case of error (invalid param,
+// out-of-memory).
+int WebPPictureAllocARGB(WebPPicture* const picture, int width, int height);
+
+// Allocates YUVA buffer of given dimension (previous one is always free'd).
+// Uses picture->csp to determine whether an alpha buffer is needed.
+// Preserves the ARGB buffer.
+// Returns false in case of error (invalid param, out-of-memory).
+int WebPPictureAllocYUVA(WebPPicture* const picture, int width, int height);
+
+  // in near_lossless.c
+// Near lossless preprocessing in RGB color-space.
+int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality);
+// Near lossless adjustment for predictors.
+void VP8ApplyNearLosslessPredict(int xsize, int ysize, int pred_bits,
+                                 const uint32_t* argb_orig,
+                                 uint32_t* argb, uint32_t* argb_scratch,
+                                 const uint32_t* const transform_data,
+                                 int quality, int subtract_green);
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/drivers/webp/enc/vp8l.c b/drivers/webp/enc/vp8l.c
index f4eb6e783f..047c9032ac 100644
--- a/drivers/webp/enc/vp8l.c
+++ b/drivers/webp/enc/vp8l.c
@@ -1,8 +1,10 @@
 // Copyright 2012 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // main entry for the lossless encoder.
@@ -11,7 +13,6 @@
 //
 
 #include <assert.h>
-#include <stdio.h>
 #include <stdlib.h>
 
 #include "./backward_references.h"
@@ -21,28 +22,107 @@
 #include "../utils/bit_writer.h"
 #include "../utils/huffman_encode.h"
 #include "../utils/utils.h"
-#include "../format_constants.h"
+#include "../webp/format_constants.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
+#include "./delta_palettization.h"
 
 #define PALETTE_KEY_RIGHT_SHIFT   22  // Key for 1K buffer.
-#define MAX_HUFF_IMAGE_SIZE       (16 * 1024 * 1024)
-#define MAX_COLORS_FOR_GRAPH      64
+// Maximum number of histogram images (sub-blocks).
+#define MAX_HUFF_IMAGE_SIZE       2600
 
-// -----------------------------------------------------------------------------
-// Palette
+// Palette reordering for smaller sum of deltas (and for smaller storage).
 
-static int CompareColors(const void* p1, const void* p2) {
+static int PaletteCompareColorsForQsort(const void* p1, const void* p2) {
   const uint32_t a = *(const uint32_t*)p1;
   const uint32_t b = *(const uint32_t*)p2;
-  return (a < b) ? -1 : (a > b) ? 1 : 0;
+  assert(a != b);
+  return (a < b) ? -1 : 1;
+}
+
+static WEBP_INLINE uint32_t PaletteComponentDistance(uint32_t v) {
+  return (v <= 128) ? v : (256 - v);
+}
+
+// Computes a value that is related to the entropy created by the
+// palette entry diff.
+//
+// Note that the last & 0xff is a no-operation in the next statement, but
+// removed by most compilers and is here only for regularity of the code.
+static WEBP_INLINE uint32_t PaletteColorDistance(uint32_t col1, uint32_t col2) {
+  const uint32_t diff = VP8LSubPixels(col1, col2);
+  const int kMoreWeightForRGBThanForAlpha = 9;
+  uint32_t score;
+  score =  PaletteComponentDistance((diff >>  0) & 0xff);
+  score += PaletteComponentDistance((diff >>  8) & 0xff);
+  score += PaletteComponentDistance((diff >> 16) & 0xff);
+  score *= kMoreWeightForRGBThanForAlpha;
+  score += PaletteComponentDistance((diff >> 24) & 0xff);
+  return score;
+}
+
+static WEBP_INLINE void SwapColor(uint32_t* const col1, uint32_t* const col2) {
+  const uint32_t tmp = *col1;
+  *col1 = *col2;
+  *col2 = tmp;
+}
+
+static void GreedyMinimizeDeltas(uint32_t palette[], int num_colors) {
+  // Find greedily always the closest color of the predicted color to minimize
+  // deltas in the palette. This reduces storage needs since the
+  // palette is stored with delta encoding.
+  uint32_t predict = 0x00000000;
+  int i, k;
+  for (i = 0; i < num_colors; ++i) {
+    int best_ix = i;
+    uint32_t best_score = ~0U;
+    for (k = i; k < num_colors; ++k) {
+      const uint32_t cur_score = PaletteColorDistance(palette[k], predict);
+      if (best_score > cur_score) {
+        best_score = cur_score;
+        best_ix = k;
+      }
+    }
+    SwapColor(&palette[best_ix], &palette[i]);
+    predict = palette[i];
+  }
+}
+
+// The palette has been sorted by alpha. This function checks if the other
+// components of the palette have a monotonic development with regards to
+// position in the palette. If all have monotonic development, there is
+// no benefit to re-organize them greedily. A monotonic development
+// would be spotted in green-only situations (like lossy alpha) or gray-scale
+// images.
+static int PaletteHasNonMonotonousDeltas(uint32_t palette[], int num_colors) {
+  uint32_t predict = 0x000000;
+  int i;
+  uint8_t sign_found = 0x00;
+  for (i = 0; i < num_colors; ++i) {
+    const uint32_t diff = VP8LSubPixels(palette[i], predict);
+    const uint8_t rd = (diff >> 16) & 0xff;
+    const uint8_t gd = (diff >>  8) & 0xff;
+    const uint8_t bd = (diff >>  0) & 0xff;
+    if (rd != 0x00) {
+      sign_found |= (rd < 0x80) ? 1 : 2;
+    }
+    if (gd != 0x00) {
+      sign_found |= (gd < 0x80) ? 8 : 16;
+    }
+    if (bd != 0x00) {
+      sign_found |= (bd < 0x80) ? 64 : 128;
+    }
+    predict = palette[i];
+  }
+  return (sign_found & (sign_found << 1)) != 0;  // two consequent signs.
 }
 
+// -----------------------------------------------------------------------------
+// Palette
+
 // If number of colors in the image is less than or equal to MAX_PALETTE_SIZE,
 // creates a palette and returns true, else returns false.
 static int AnalyzeAndCreatePalette(const WebPPicture* const pic,
+                                   int low_effort,
                                    uint32_t palette[MAX_PALETTE_SIZE],
                                    int* const palette_size) {
   int i, x, y, key;
@@ -85,7 +165,7 @@ static int AnalyzeAndCreatePalette(const WebPPicture* const pic,
     argb += pic->argb_stride;
   }
 
-  // TODO(skal): could we reuse in_use[] to speed up ApplyPalette()?
+  // TODO(skal): could we reuse in_use[] to speed up EncodePalette()?
   num_colors = 0;
   for (i = 0; i < (int)(sizeof(in_use) / sizeof(in_use[0])); ++i) {
     if (in_use[i]) {
@@ -93,106 +173,272 @@ static int AnalyzeAndCreatePalette(const WebPPicture* const pic,
       ++num_colors;
     }
   }
-
-  qsort(palette, num_colors, sizeof(*palette), CompareColors);
   *palette_size = num_colors;
+  qsort(palette, num_colors, sizeof(*palette), PaletteCompareColorsForQsort);
+  if (!low_effort && PaletteHasNonMonotonousDeltas(palette, num_colors)) {
+    GreedyMinimizeDeltas(palette, num_colors);
+  }
   return 1;
 }
 
+// These five modes are evaluated and their respective entropy is computed.
+typedef enum {
+  kDirect = 0,
+  kSpatial = 1,
+  kSubGreen = 2,
+  kSpatialSubGreen = 3,
+  kPalette = 4,
+  kNumEntropyIx = 5
+} EntropyIx;
+
+typedef enum {
+  kHistoAlpha = 0,
+  kHistoAlphaPred,
+  kHistoGreen,
+  kHistoGreenPred,
+  kHistoRed,
+  kHistoRedPred,
+  kHistoBlue,
+  kHistoBluePred,
+  kHistoRedSubGreen,
+  kHistoRedPredSubGreen,
+  kHistoBlueSubGreen,
+  kHistoBluePredSubGreen,
+  kHistoPalette,
+  kHistoTotal  // Must be last.
+} HistoIx;
+
+static void AddSingleSubGreen(uint32_t p, uint32_t* r, uint32_t* b) {
+  const uint32_t green = p >> 8;  // The upper bits are masked away later.
+  ++r[((p >> 16) - green) & 0xff];
+  ++b[(p - green) & 0xff];
+}
+
+static void AddSingle(uint32_t p,
+                      uint32_t* a, uint32_t* r, uint32_t* g, uint32_t* b) {
+  ++a[p >> 24];
+  ++r[(p >> 16) & 0xff];
+  ++g[(p >> 8) & 0xff];
+  ++b[(p & 0xff)];
+}
+
 static int AnalyzeEntropy(const uint32_t* argb,
                           int width, int height, int argb_stride,
-                          double* const nonpredicted_bits,
-                          double* const predicted_bits) {
-  int x, y;
-  const uint32_t* last_line = NULL;
-  uint32_t last_pix = argb[0];    // so we're sure that pix_diff == 0
-
-  VP8LHistogram* nonpredicted = NULL;
-  VP8LHistogram* predicted =
-      (VP8LHistogram*)malloc(2 * sizeof(*predicted));
-  if (predicted == NULL) return 0;
-  nonpredicted = predicted + 1;
-
-  VP8LHistogramInit(predicted, 0);
-  VP8LHistogramInit(nonpredicted, 0);
-  for (y = 0; y < height; ++y) {
-    for (x = 0; x < width; ++x) {
-      const uint32_t pix = argb[x];
-      const uint32_t pix_diff = VP8LSubPixels(pix, last_pix);
-      if (pix_diff == 0) continue;
-      if (last_line != NULL && pix == last_line[x]) {
-        continue;
+                          int use_palette,
+                          EntropyIx* const min_entropy_ix,
+                          int* const red_and_blue_always_zero) {
+  // Allocate histogram set with cache_bits = 0.
+  uint32_t* const histo =
+      (uint32_t*)WebPSafeCalloc(kHistoTotal, sizeof(*histo) * 256);
+  if (histo != NULL) {
+    int i, x, y;
+    const uint32_t* prev_row = argb;
+    const uint32_t* curr_row = argb + argb_stride;
+    for (y = 1; y < height; ++y) {
+      uint32_t prev_pix = curr_row[0];
+      for (x = 1; x < width; ++x) {
+        const uint32_t pix = curr_row[x];
+        const uint32_t pix_diff = VP8LSubPixels(pix, prev_pix);
+        if ((pix_diff == 0) || (pix == prev_row[x])) continue;
+        prev_pix = pix;
+        AddSingle(pix,
+                  &histo[kHistoAlpha * 256],
+                  &histo[kHistoRed * 256],
+                  &histo[kHistoGreen * 256],
+                  &histo[kHistoBlue * 256]);
+        AddSingle(pix_diff,
+                  &histo[kHistoAlphaPred * 256],
+                  &histo[kHistoRedPred * 256],
+                  &histo[kHistoGreenPred * 256],
+                  &histo[kHistoBluePred * 256]);
+        AddSingleSubGreen(pix,
+                          &histo[kHistoRedSubGreen * 256],
+                          &histo[kHistoBlueSubGreen * 256]);
+        AddSingleSubGreen(pix_diff,
+                          &histo[kHistoRedPredSubGreen * 256],
+                          &histo[kHistoBluePredSubGreen * 256]);
+        {
+          // Approximate the palette by the entropy of the multiplicative hash.
+          const int hash = ((pix + (pix >> 19)) * 0x39c5fba7) >> 24;
+          ++histo[kHistoPalette * 256 + (hash & 0xff)];
+        }
+      }
+      prev_row = curr_row;
+      curr_row += argb_stride;
+    }
+    {
+      double entropy_comp[kHistoTotal];
+      double entropy[kNumEntropyIx];
+      EntropyIx k;
+      EntropyIx last_mode_to_analyze =
+          use_palette ? kPalette : kSpatialSubGreen;
+      int j;
+      // Let's add one zero to the predicted histograms. The zeros are removed
+      // too efficiently by the pix_diff == 0 comparison, at least one of the
+      // zeros is likely to exist.
+      ++histo[kHistoRedPredSubGreen * 256];
+      ++histo[kHistoBluePredSubGreen * 256];
+      ++histo[kHistoRedPred * 256];
+      ++histo[kHistoGreenPred * 256];
+      ++histo[kHistoBluePred * 256];
+      ++histo[kHistoAlphaPred * 256];
+
+      for (j = 0; j < kHistoTotal; ++j) {
+        entropy_comp[j] = VP8LBitsEntropy(&histo[j * 256], 256, NULL);
+      }
+      entropy[kDirect] = entropy_comp[kHistoAlpha] +
+          entropy_comp[kHistoRed] +
+          entropy_comp[kHistoGreen] +
+          entropy_comp[kHistoBlue];
+      entropy[kSpatial] = entropy_comp[kHistoAlphaPred] +
+          entropy_comp[kHistoRedPred] +
+          entropy_comp[kHistoGreenPred] +
+          entropy_comp[kHistoBluePred];
+      entropy[kSubGreen] = entropy_comp[kHistoAlpha] +
+          entropy_comp[kHistoRedSubGreen] +
+          entropy_comp[kHistoGreen] +
+          entropy_comp[kHistoBlueSubGreen];
+      entropy[kSpatialSubGreen] = entropy_comp[kHistoAlphaPred] +
+          entropy_comp[kHistoRedPredSubGreen] +
+          entropy_comp[kHistoGreenPred] +
+          entropy_comp[kHistoBluePredSubGreen];
+      // Palette mode seems more efficient in a breakeven case. Bias with 1.0.
+      entropy[kPalette] = entropy_comp[kHistoPalette] - 1.0;
+
+      *min_entropy_ix = kDirect;
+      for (k = kDirect + 1; k <= last_mode_to_analyze; ++k) {
+        if (entropy[*min_entropy_ix] > entropy[k]) {
+          *min_entropy_ix = k;
+        }
       }
-      last_pix = pix;
+      *red_and_blue_always_zero = 1;
+      // Let's check if the histogram of the chosen entropy mode has
+      // non-zero red and blue values. If all are zero, we can later skip
+      // the cross color optimization.
       {
-        const PixOrCopy pix_token = PixOrCopyCreateLiteral(pix);
-        const PixOrCopy pix_diff_token = PixOrCopyCreateLiteral(pix_diff);
-        VP8LHistogramAddSinglePixOrCopy(nonpredicted, &pix_token);
-        VP8LHistogramAddSinglePixOrCopy(predicted, &pix_diff_token);
+        static const uint8_t kHistoPairs[5][2] = {
+          { kHistoRed, kHistoBlue },
+          { kHistoRedPred, kHistoBluePred },
+          { kHistoRedSubGreen, kHistoBlueSubGreen },
+          { kHistoRedPredSubGreen, kHistoBluePredSubGreen },
+          { kHistoRed, kHistoBlue }
+        };
+        const uint32_t* const red_histo =
+            &histo[256 * kHistoPairs[*min_entropy_ix][0]];
+        const uint32_t* const blue_histo =
+            &histo[256 * kHistoPairs[*min_entropy_ix][1]];
+        for (i = 1; i < 256; ++i) {
+          if ((red_histo[i] | blue_histo[i]) != 0) {
+            *red_and_blue_always_zero = 0;
+            break;
+          }
+        }
       }
     }
-    last_line = argb;
-    argb += argb_stride;
+    free(histo);
+    return 1;
+  } else {
+    return 0;
   }
-  *nonpredicted_bits = VP8LHistogramEstimateBitsBulk(nonpredicted);
-  *predicted_bits = VP8LHistogramEstimateBitsBulk(predicted);
-  free(predicted);
-  return 1;
 }
 
-static int VP8LEncAnalyze(VP8LEncoder* const enc, WebPImageHint image_hint) {
+static int GetHistoBits(int method, int use_palette, int width, int height) {
+  // Make tile size a function of encoding method (Range: 0 to 6).
+  int histo_bits = (use_palette ? 9 : 7) - method;
+  while (1) {
+    const int huff_image_size = VP8LSubSampleSize(width, histo_bits) *
+                                VP8LSubSampleSize(height, histo_bits);
+    if (huff_image_size <= MAX_HUFF_IMAGE_SIZE) break;
+    ++histo_bits;
+  }
+  return (histo_bits < MIN_HUFFMAN_BITS) ? MIN_HUFFMAN_BITS :
+         (histo_bits > MAX_HUFFMAN_BITS) ? MAX_HUFFMAN_BITS : histo_bits;
+}
+
+static int GetTransformBits(int method, int histo_bits) {
+  const int max_transform_bits = (method < 4) ? 6 : (method > 4) ? 4 : 5;
+  return (histo_bits > max_transform_bits) ? max_transform_bits : histo_bits;
+}
+
+static int AnalyzeAndInit(VP8LEncoder* const enc) {
   const WebPPicture* const pic = enc->pic_;
+  const int width = pic->width;
+  const int height = pic->height;
+  const int pix_cnt = width * height;
+  const WebPConfig* const config = enc->config_;
+  const int method = config->method;
+  const int low_effort = (config->method == 0);
+  // we round the block size up, so we're guaranteed to have
+  // at max MAX_REFS_BLOCK_PER_IMAGE blocks used:
+  int refs_block_size = (pix_cnt - 1) / MAX_REFS_BLOCK_PER_IMAGE + 1;
   assert(pic != NULL && pic->argb != NULL);
 
+  enc->use_cross_color_ = 0;
+  enc->use_predict_ = 0;
+  enc->use_subtract_green_ = 0;
   enc->use_palette_ =
-      AnalyzeAndCreatePalette(pic, enc->palette_, &enc->palette_size_);
-
-  if (image_hint == WEBP_HINT_GRAPH) {
-    if (enc->use_palette_ && enc->palette_size_ < MAX_COLORS_FOR_GRAPH) {
-      enc->use_palette_ = 0;
+      AnalyzeAndCreatePalette(pic, low_effort,
+                              enc->palette_, &enc->palette_size_);
+
+  // TODO(jyrki): replace the decision to be based on an actual estimate
+  // of entropy, or even spatial variance of entropy.
+  enc->histo_bits_ = GetHistoBits(method, enc->use_palette_,
+                                  pic->width, pic->height);
+  enc->transform_bits_ = GetTransformBits(method, enc->histo_bits_);
+
+  if (low_effort) {
+    // AnalyzeEntropy is somewhat slow.
+    enc->use_predict_ = !enc->use_palette_;
+    enc->use_subtract_green_ = !enc->use_palette_;
+    enc->use_cross_color_ = 0;
+  } else {
+    int red_and_blue_always_zero;
+    EntropyIx min_entropy_ix;
+    if (!AnalyzeEntropy(pic->argb, width, height, pic->argb_stride,
+                        enc->use_palette_, &min_entropy_ix,
+                        &red_and_blue_always_zero)) {
+      return 0;
     }
+    enc->use_palette_ = (min_entropy_ix == kPalette);
+    enc->use_subtract_green_ =
+        (min_entropy_ix == kSubGreen) || (min_entropy_ix == kSpatialSubGreen);
+    enc->use_predict_ =
+        (min_entropy_ix == kSpatial) || (min_entropy_ix == kSpatialSubGreen);
+    enc->use_cross_color_ = red_and_blue_always_zero ? 0 : enc->use_predict_;
   }
 
-  if (!enc->use_palette_) {
-    if (image_hint == WEBP_HINT_PHOTO) {
-      enc->use_predict_ = 1;
-      enc->use_cross_color_ = 1;
-    } else {
-      double non_pred_entropy, pred_entropy;
-      if (!AnalyzeEntropy(pic->argb, pic->width, pic->height, pic->argb_stride,
-                          &non_pred_entropy, &pred_entropy)) {
-        return 0;
-      }
-      if (pred_entropy < 0.95 * non_pred_entropy) {
-        enc->use_predict_ = 1;
-        // TODO(vikasa): Observed some correlation of cross_color transform with
-        // predict. Need to investigate this further and add separate heuristic
-        // for setting use_cross_color flag.
-        enc->use_cross_color_ = 1;
-      }
-    }
-  }
+  if (!VP8LHashChainInit(&enc->hash_chain_, pix_cnt)) return 0;
+
+  // palette-friendly input typically uses less literals
+  //  -> reduce block size a bit
+  if (enc->use_palette_) refs_block_size /= 2;
+  VP8LBackwardRefsInit(&enc->refs_[0], refs_block_size);
+  VP8LBackwardRefsInit(&enc->refs_[1], refs_block_size);
 
   return 1;
 }
 
+// Returns false in case of memory error.
 static int GetHuffBitLengthsAndCodes(
     const VP8LHistogramSet* const histogram_image,
     HuffmanTreeCode* const huffman_codes) {
   int i, k;
-  int ok = 1;
+  int ok = 0;
   uint64_t total_length_size = 0;
   uint8_t* mem_buf = NULL;
   const int histogram_image_size = histogram_image->size;
+  int max_num_symbols = 0;
+  uint8_t* buf_rle = NULL;
+  HuffmanTree* huff_tree = NULL;
 
   // Iterate over all histograms and get the aggregate number of codes used.
   for (i = 0; i < histogram_image_size; ++i) {
     const VP8LHistogram* const histo = histogram_image->histograms[i];
     HuffmanTreeCode* const codes = &huffman_codes[5 * i];
     for (k = 0; k < 5; ++k) {
-      const int num_symbols = (k == 0) ? VP8LHistogramNumCodes(histo)
-                            : (k == 4) ? NUM_DISTANCE_CODES
-                            : 256;
+      const int num_symbols =
+          (k == 0) ? VP8LHistogramNumCodes(histo->palette_code_bits_) :
+          (k == 4) ? NUM_DISTANCE_CODES : 256;
       codes[k].num_symbols = num_symbols;
       total_length_size += num_symbols;
     }
@@ -204,10 +450,8 @@ static int GetHuffBitLengthsAndCodes(
     uint8_t* lengths;
     mem_buf = (uint8_t*)WebPSafeCalloc(total_length_size,
                                        sizeof(*lengths) + sizeof(*codes));
-    if (mem_buf == NULL) {
-      ok = 0;
-      goto End;
-    }
+    if (mem_buf == NULL) goto End;
+
     codes = (uint16_t*)mem_buf;
     lengths = (uint8_t*)&codes[total_length_size];
     for (i = 0; i < 5 * histogram_image_size; ++i) {
@@ -216,22 +460,35 @@ static int GetHuffBitLengthsAndCodes(
       huffman_codes[i].code_lengths = lengths;
       codes += bit_length;
       lengths += bit_length;
+      if (max_num_symbols < bit_length) {
+        max_num_symbols = bit_length;
+      }
     }
   }
 
+  buf_rle = (uint8_t*)WebPSafeMalloc(1ULL, max_num_symbols);
+  huff_tree = (HuffmanTree*)WebPSafeMalloc(3ULL * max_num_symbols,
+                                           sizeof(*huff_tree));
+  if (buf_rle == NULL || huff_tree == NULL) goto End;
+
   // Create Huffman trees.
   for (i = 0; i < histogram_image_size; ++i) {
     HuffmanTreeCode* const codes = &huffman_codes[5 * i];
     VP8LHistogram* const histo = histogram_image->histograms[i];
-    ok = ok && VP8LCreateHuffmanTree(histo->literal_, 15, codes + 0);
-    ok = ok && VP8LCreateHuffmanTree(histo->red_, 15, codes + 1);
-    ok = ok && VP8LCreateHuffmanTree(histo->blue_, 15, codes + 2);
-    ok = ok && VP8LCreateHuffmanTree(histo->alpha_, 15, codes + 3);
-    ok = ok && VP8LCreateHuffmanTree(histo->distance_, 15, codes + 4);
+    VP8LCreateHuffmanTree(histo->literal_, 15, buf_rle, huff_tree, codes + 0);
+    VP8LCreateHuffmanTree(histo->red_, 15, buf_rle, huff_tree, codes + 1);
+    VP8LCreateHuffmanTree(histo->blue_, 15, buf_rle, huff_tree, codes + 2);
+    VP8LCreateHuffmanTree(histo->alpha_, 15, buf_rle, huff_tree, codes + 3);
+    VP8LCreateHuffmanTree(histo->distance_, 15, buf_rle, huff_tree, codes + 4);
   }
-
+  ok = 1;
  End:
-  if (!ok) free(mem_buf);
+  WebPSafeFree(huff_tree);
+  WebPSafeFree(buf_rle);
+  if (!ok) {
+    WebPSafeFree(mem_buf);
+    memset(huffman_codes, 0, 5 * histogram_image_size * sizeof(*huffman_codes));
+  }
   return ok;
 }
 
@@ -251,9 +508,9 @@ static void StoreHuffmanTreeOfHuffmanTreeToBitMask(
       break;
     }
   }
-  VP8LWriteBits(bw, 4, codes_to_store - 4);
+  VP8LPutBits(bw, codes_to_store - 4, 4);
   for (i = 0; i < codes_to_store; ++i) {
-    VP8LWriteBits(bw, 3, code_length_bitdepth[kStorageOrder[i]]);
+    VP8LPutBits(bw, code_length_bitdepth[kStorageOrder[i]], 3);
   }
 }
 
@@ -281,49 +538,46 @@ static void StoreHuffmanTreeToBitMask(
   for (i = 0; i < num_tokens; ++i) {
     const int ix = tokens[i].code;
     const int extra_bits = tokens[i].extra_bits;
-    VP8LWriteBits(bw, huffman_code->code_lengths[ix], huffman_code->codes[ix]);
+    VP8LPutBits(bw, huffman_code->codes[ix], huffman_code->code_lengths[ix]);
     switch (ix) {
       case 16:
-        VP8LWriteBits(bw, 2, extra_bits);
+        VP8LPutBits(bw, extra_bits, 2);
         break;
       case 17:
-        VP8LWriteBits(bw, 3, extra_bits);
+        VP8LPutBits(bw, extra_bits, 3);
         break;
       case 18:
-        VP8LWriteBits(bw, 7, extra_bits);
+        VP8LPutBits(bw, extra_bits, 7);
         break;
     }
   }
 }
 
-static int StoreFullHuffmanCode(VP8LBitWriter* const bw,
-                                const HuffmanTreeCode* const tree) {
-  int ok = 0;
+// 'huff_tree' and 'tokens' are pre-alloacted buffers.
+static void StoreFullHuffmanCode(VP8LBitWriter* const bw,
+                                 HuffmanTree* const huff_tree,
+                                 HuffmanTreeToken* const tokens,
+                                 const HuffmanTreeCode* const tree) {
   uint8_t code_length_bitdepth[CODE_LENGTH_CODES] = { 0 };
   uint16_t code_length_bitdepth_symbols[CODE_LENGTH_CODES] = { 0 };
   const int max_tokens = tree->num_symbols;
   int num_tokens;
   HuffmanTreeCode huffman_code;
-  HuffmanTreeToken* const tokens =
-      (HuffmanTreeToken*)WebPSafeMalloc((uint64_t)max_tokens, sizeof(*tokens));
-  if (tokens == NULL) return 0;
-
   huffman_code.num_symbols = CODE_LENGTH_CODES;
   huffman_code.code_lengths = code_length_bitdepth;
   huffman_code.codes = code_length_bitdepth_symbols;
 
-  VP8LWriteBits(bw, 1, 0);
+  VP8LPutBits(bw, 0, 1);
   num_tokens = VP8LCreateCompressedHuffmanTree(tree, tokens, max_tokens);
   {
-    int histogram[CODE_LENGTH_CODES] = { 0 };
+    uint32_t histogram[CODE_LENGTH_CODES] = { 0 };
+    uint8_t buf_rle[CODE_LENGTH_CODES] = { 0 };
     int i;
     for (i = 0; i < num_tokens; ++i) {
       ++histogram[tokens[i].code];
     }
 
-    if (!VP8LCreateHuffmanTree(histogram, 7, &huffman_code)) {
-      goto End;
-    }
+    VP8LCreateHuffmanTree(histogram, 7, buf_rle, huff_tree, &huffman_code);
   }
 
   StoreHuffmanTreeOfHuffmanTreeToBitMask(bw, code_length_bitdepth);
@@ -350,24 +604,23 @@ static int StoreFullHuffmanCode(VP8LBitWriter* const bw,
     }
     write_trimmed_length = (trimmed_length > 1 && trailing_zero_bits > 12);
     length = write_trimmed_length ? trimmed_length : num_tokens;
-    VP8LWriteBits(bw, 1, write_trimmed_length);
+    VP8LPutBits(bw, write_trimmed_length, 1);
     if (write_trimmed_length) {
       const int nbits = VP8LBitsLog2Ceiling(trimmed_length - 1);
       const int nbitpairs = (nbits == 0) ? 1 : (nbits + 1) / 2;
-      VP8LWriteBits(bw, 3, nbitpairs - 1);
+      VP8LPutBits(bw, nbitpairs - 1, 3);
       assert(trimmed_length >= 2);
-      VP8LWriteBits(bw, nbitpairs * 2, trimmed_length - 2);
+      VP8LPutBits(bw, trimmed_length - 2, nbitpairs * 2);
     }
     StoreHuffmanTreeToBitMask(bw, tokens, length, &huffman_code);
   }
-  ok = 1;
- End:
-  free(tokens);
-  return ok;
 }
 
-static int StoreHuffmanCode(VP8LBitWriter* const bw,
-                            const HuffmanTreeCode* const huffman_code) {
+// 'huff_tree' and 'tokens' are pre-alloacted buffers.
+static void StoreHuffmanCode(VP8LBitWriter* const bw,
+                             HuffmanTree* const huff_tree,
+                             HuffmanTreeToken* const tokens,
+                             const HuffmanTreeCode* const huffman_code) {
   int i;
   int count = 0;
   int symbols[2] = { 0, 0 };
@@ -384,163 +637,248 @@ static int StoreHuffmanCode(VP8LBitWriter* const bw,
 
   if (count == 0) {   // emit minimal tree for empty cases
     // bits: small tree marker: 1, count-1: 0, large 8-bit code: 0, code: 0
-    VP8LWriteBits(bw, 4, 0x01);
-    return 1;
+    VP8LPutBits(bw, 0x01, 4);
   } else if (count <= 2 && symbols[0] < kMaxSymbol && symbols[1] < kMaxSymbol) {
-    VP8LWriteBits(bw, 1, 1);  // Small tree marker to encode 1 or 2 symbols.
-    VP8LWriteBits(bw, 1, count - 1);
+    VP8LPutBits(bw, 1, 1);  // Small tree marker to encode 1 or 2 symbols.
+    VP8LPutBits(bw, count - 1, 1);
     if (symbols[0] <= 1) {
-      VP8LWriteBits(bw, 1, 0);  // Code bit for small (1 bit) symbol value.
-      VP8LWriteBits(bw, 1, symbols[0]);
+      VP8LPutBits(bw, 0, 1);  // Code bit for small (1 bit) symbol value.
+      VP8LPutBits(bw, symbols[0], 1);
     } else {
-      VP8LWriteBits(bw, 1, 1);
-      VP8LWriteBits(bw, 8, symbols[0]);
+      VP8LPutBits(bw, 1, 1);
+      VP8LPutBits(bw, symbols[0], 8);
     }
     if (count == 2) {
-      VP8LWriteBits(bw, 8, symbols[1]);
+      VP8LPutBits(bw, symbols[1], 8);
     }
-    return 1;
   } else {
-    return StoreFullHuffmanCode(bw, huffman_code);
+    StoreFullHuffmanCode(bw, huff_tree, tokens, huffman_code);
   }
 }
 
-static void WriteHuffmanCode(VP8LBitWriter* const bw,
-                             const HuffmanTreeCode* const code, int index) {
-  const int depth = code->code_lengths[index];
-  const int symbol = code->codes[index];
-  VP8LWriteBits(bw, depth, symbol);
+static WEBP_INLINE void WriteHuffmanCode(VP8LBitWriter* const bw,
+                             const HuffmanTreeCode* const code,
+                             int code_index) {
+  const int depth = code->code_lengths[code_index];
+  const int symbol = code->codes[code_index];
+  VP8LPutBits(bw, symbol, depth);
 }
 
-static void StoreImageToBitMask(
+static WEBP_INLINE void WriteHuffmanCodeWithExtraBits(
+    VP8LBitWriter* const bw,
+    const HuffmanTreeCode* const code,
+    int code_index,
+    int bits,
+    int n_bits) {
+  const int depth = code->code_lengths[code_index];
+  const int symbol = code->codes[code_index];
+  VP8LPutBits(bw, (bits << depth) | symbol, depth + n_bits);
+}
+
+static WebPEncodingError StoreImageToBitMask(
     VP8LBitWriter* const bw, int width, int histo_bits,
-    const VP8LBackwardRefs* const refs,
+    VP8LBackwardRefs* const refs,
     const uint16_t* histogram_symbols,
     const HuffmanTreeCode* const huffman_codes) {
+  const int histo_xsize = histo_bits ? VP8LSubSampleSize(width, histo_bits) : 1;
+  const int tile_mask = (histo_bits == 0) ? 0 : -(1 << histo_bits);
   // x and y trace the position in the image.
   int x = 0;
   int y = 0;
-  const int histo_xsize = histo_bits ? VP8LSubSampleSize(width, histo_bits) : 1;
-  int i;
-  for (i = 0; i < refs->size; ++i) {
-    const PixOrCopy* const v = &refs->refs[i];
-    const int histogram_ix = histogram_symbols[histo_bits ?
-                                               (y >> histo_bits) * histo_xsize +
-                                               (x >> histo_bits) : 0];
-    const HuffmanTreeCode* const codes = huffman_codes + 5 * histogram_ix;
-    if (PixOrCopyIsCacheIdx(v)) {
-      const int code = PixOrCopyCacheIdx(v);
-      const int literal_ix = 256 + NUM_LENGTH_CODES + code;
-      WriteHuffmanCode(bw, codes, literal_ix);
-    } else if (PixOrCopyIsLiteral(v)) {
+  int tile_x = x & tile_mask;
+  int tile_y = y & tile_mask;
+  int histogram_ix = histogram_symbols[0];
+  const HuffmanTreeCode* codes = huffman_codes + 5 * histogram_ix;
+  VP8LRefsCursor c = VP8LRefsCursorInit(refs);
+  while (VP8LRefsCursorOk(&c)) {
+    const PixOrCopy* const v = c.cur_pos;
+    if ((tile_x != (x & tile_mask)) || (tile_y != (y & tile_mask))) {
+      tile_x = x & tile_mask;
+      tile_y = y & tile_mask;
+      histogram_ix = histogram_symbols[(y >> histo_bits) * histo_xsize +
+                                       (x >> histo_bits)];
+      codes = huffman_codes + 5 * histogram_ix;
+    }
+    if (PixOrCopyIsLiteral(v)) {
       static const int order[] = { 1, 2, 0, 3 };
       int k;
       for (k = 0; k < 4; ++k) {
         const int code = PixOrCopyLiteral(v, order[k]);
         WriteHuffmanCode(bw, codes + k, code);
       }
+    } else if (PixOrCopyIsCacheIdx(v)) {
+      const int code = PixOrCopyCacheIdx(v);
+      const int literal_ix = 256 + NUM_LENGTH_CODES + code;
+      WriteHuffmanCode(bw, codes, literal_ix);
     } else {
       int bits, n_bits;
-      int code, distance;
+      int code;
 
-      PrefixEncode(v->len, &code, &n_bits, &bits);
-      WriteHuffmanCode(bw, codes, 256 + code);
-      VP8LWriteBits(bw, n_bits, bits);
+      const int distance = PixOrCopyDistance(v);
+      VP8LPrefixEncode(v->len, &code, &n_bits, &bits);
+      WriteHuffmanCodeWithExtraBits(bw, codes, 256 + code, bits, n_bits);
 
-      distance = PixOrCopyDistance(v);
-      PrefixEncode(distance, &code, &n_bits, &bits);
+      // Don't write the distance with the extra bits code since
+      // the distance can be up to 18 bits of extra bits, and the prefix
+      // 15 bits, totaling to 33, and our PutBits only supports up to 32 bits.
+      // TODO(jyrki): optimize this further.
+      VP8LPrefixEncode(distance, &code, &n_bits, &bits);
       WriteHuffmanCode(bw, codes + 4, code);
-      VP8LWriteBits(bw, n_bits, bits);
+      VP8LPutBits(bw, bits, n_bits);
     }
     x += PixOrCopyLength(v);
     while (x >= width) {
       x -= width;
       ++y;
     }
+    VP8LRefsCursorNext(&c);
   }
+  return bw->error_ ? VP8_ENC_ERROR_OUT_OF_MEMORY : VP8_ENC_OK;
 }
 
 // Special case of EncodeImageInternal() for cache-bits=0, histo_bits=31
-static int EncodeImageNoHuffman(VP8LBitWriter* const bw,
-                                const uint32_t* const argb,
-                                int width, int height, int quality) {
+static WebPEncodingError EncodeImageNoHuffman(VP8LBitWriter* const bw,
+                                              const uint32_t* const argb,
+                                              VP8LHashChain* const hash_chain,
+                                              VP8LBackwardRefs refs_array[2],
+                                              int width, int height,
+                                              int quality) {
   int i;
-  int ok = 0;
-  VP8LBackwardRefs refs;
+  int max_tokens = 0;
+  WebPEncodingError err = VP8_ENC_OK;
+  VP8LBackwardRefs* refs;
+  HuffmanTreeToken* tokens = NULL;
   HuffmanTreeCode huffman_codes[5] = { { 0, NULL, NULL } };
   const uint16_t histogram_symbols[1] = { 0 };    // only one tree, one symbol
-  VP8LHistogramSet* const histogram_image = VP8LAllocateHistogramSet(1, 0);
-  if (histogram_image == NULL) return 0;
+  int cache_bits = 0;
+  VP8LHistogramSet* histogram_image = NULL;
+  HuffmanTree* const huff_tree = (HuffmanTree*)WebPSafeMalloc(
+        3ULL * CODE_LENGTH_CODES, sizeof(*huff_tree));
+  if (huff_tree == NULL) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+    goto Error;
+  }
 
   // Calculate backward references from ARGB image.
-  if (!VP8LGetBackwardReferences(width, height, argb, quality, 0, 1, &refs)) {
+  refs = VP8LGetBackwardReferences(width, height, argb, quality, 0, &cache_bits,
+                                   hash_chain, refs_array);
+  if (refs == NULL) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
+  histogram_image = VP8LAllocateHistogramSet(1, cache_bits);
+  if (histogram_image == NULL) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+    goto Error;
+  }
+
   // Build histogram image and symbols from backward references.
-  VP8LHistogramStoreRefs(&refs, histogram_image->histograms[0]);
+  VP8LHistogramStoreRefs(refs, histogram_image->histograms[0]);
 
   // Create Huffman bit lengths and codes for each histogram image.
   assert(histogram_image->size == 1);
   if (!GetHuffBitLengthsAndCodes(histogram_image, huffman_codes)) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
 
   // No color cache, no Huffman image.
-  VP8LWriteBits(bw, 1, 0);
+  VP8LPutBits(bw, 0, 1);
 
-  // Store Huffman codes.
+  // Find maximum number of symbols for the huffman tree-set.
   for (i = 0; i < 5; ++i) {
     HuffmanTreeCode* const codes = &huffman_codes[i];
-    if (!StoreHuffmanCode(bw, codes)) {
-      goto Error;
+    if (max_tokens < codes->num_symbols) {
+      max_tokens = codes->num_symbols;
     }
+  }
+
+  tokens = (HuffmanTreeToken*)WebPSafeMalloc(max_tokens, sizeof(*tokens));
+  if (tokens == NULL) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+    goto Error;
+  }
+
+  // Store Huffman codes.
+  for (i = 0; i < 5; ++i) {
+    HuffmanTreeCode* const codes = &huffman_codes[i];
+    StoreHuffmanCode(bw, huff_tree, tokens, codes);
     ClearHuffmanTreeIfOnlyOneSymbol(codes);
   }
 
   // Store actual literals.
-  StoreImageToBitMask(bw, width, 0, &refs, histogram_symbols, huffman_codes);
-  ok = 1;
+  err = StoreImageToBitMask(bw, width, 0, refs, histogram_symbols,
+                            huffman_codes);
 
  Error:
-  free(histogram_image);
-  VP8LClearBackwardRefs(&refs);
-  free(huffman_codes[0].codes);
-  return ok;
+  WebPSafeFree(tokens);
+  WebPSafeFree(huff_tree);
+  VP8LFreeHistogramSet(histogram_image);
+  WebPSafeFree(huffman_codes[0].codes);
+  return err;
 }
 
-static int EncodeImageInternal(VP8LBitWriter* const bw,
-                               const uint32_t* const argb,
-                               int width, int height, int quality,
-                               int cache_bits, int histogram_bits) {
-  int ok = 0;
-  const int use_2d_locality = 1;
-  const int use_color_cache = (cache_bits > 0);
+static WebPEncodingError EncodeImageInternal(VP8LBitWriter* const bw,
+                                             const uint32_t* const argb,
+                                             VP8LHashChain* const hash_chain,
+                                             VP8LBackwardRefs refs_array[2],
+                                             int width, int height, int quality,
+                                             int low_effort, int* cache_bits,
+                                             int histogram_bits,
+                                             size_t init_byte_position,
+                                             int* const hdr_size,
+                                             int* const data_size) {
+  WebPEncodingError err = VP8_ENC_OK;
   const uint32_t histogram_image_xysize =
       VP8LSubSampleSize(width, histogram_bits) *
       VP8LSubSampleSize(height, histogram_bits);
-  VP8LHistogramSet* histogram_image =
-      VP8LAllocateHistogramSet(histogram_image_xysize, 0);
+  VP8LHistogramSet* histogram_image = NULL;
+  VP8LHistogramSet* tmp_histos = NULL;
   int histogram_image_size = 0;
   size_t bit_array_size = 0;
+  HuffmanTree* huff_tree = NULL;
+  HuffmanTreeToken* tokens = NULL;
   HuffmanTreeCode* huffman_codes = NULL;
   VP8LBackwardRefs refs;
+  VP8LBackwardRefs* best_refs;
   uint16_t* const histogram_symbols =
-      (uint16_t*)WebPSafeMalloc((uint64_t)histogram_image_xysize,
+      (uint16_t*)WebPSafeMalloc(histogram_image_xysize,
                                 sizeof(*histogram_symbols));
   assert(histogram_bits >= MIN_HUFFMAN_BITS);
   assert(histogram_bits <= MAX_HUFFMAN_BITS);
-  if (histogram_image == NULL || histogram_symbols == NULL) goto Error;
+  assert(hdr_size != NULL);
+  assert(data_size != NULL);
 
+  VP8LBackwardRefsInit(&refs, refs_array[0].block_size_);
+  if (histogram_symbols == NULL) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+    goto Error;
+  }
+
+  *cache_bits = MAX_COLOR_CACHE_BITS;
+  // 'best_refs' is the reference to the best backward refs and points to one
+  // of refs_array[0] or refs_array[1].
   // Calculate backward references from ARGB image.
-  if (!VP8LGetBackwardReferences(width, height, argb, quality, cache_bits,
-                                 use_2d_locality, &refs)) {
+  best_refs = VP8LGetBackwardReferences(width, height, argb, quality,
+                                        low_effort, cache_bits, hash_chain,
+                                        refs_array);
+  if (best_refs == NULL || !VP8LBackwardRefsCopy(best_refs, &refs)) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
+  histogram_image =
+      VP8LAllocateHistogramSet(histogram_image_xysize, *cache_bits);
+  tmp_histos = VP8LAllocateHistogramSet(2, *cache_bits);
+  if (histogram_image == NULL || tmp_histos == NULL) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+    goto Error;
+  }
+
   // Build histogram image and symbols from backward references.
-  if (!VP8LGetHistoImageSymbols(width, height, &refs,
-                                quality, histogram_bits, cache_bits,
-                                histogram_image,
-                                histogram_symbols)) {
+  if (!VP8LGetHistoImageSymbols(width, height, &refs, quality, low_effort,
+                                histogram_bits, *cache_bits, histogram_image,
+                                tmp_histos, histogram_symbols)) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
   // Create Huffman bit lengths and codes for each histogram image.
@@ -548,171 +886,167 @@ static int EncodeImageInternal(VP8LBitWriter* const bw,
   bit_array_size = 5 * histogram_image_size;
   huffman_codes = (HuffmanTreeCode*)WebPSafeCalloc(bit_array_size,
                                                    sizeof(*huffman_codes));
+  // Note: some histogram_image entries may point to tmp_histos[], so the latter
+  // need to outlive the following call to GetHuffBitLengthsAndCodes().
   if (huffman_codes == NULL ||
       !GetHuffBitLengthsAndCodes(histogram_image, huffman_codes)) {
+    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
+  // Free combined histograms.
+  VP8LFreeHistogramSet(histogram_image);
+  histogram_image = NULL;
+
+  // Free scratch histograms.
+  VP8LFreeHistogramSet(tmp_histos);
+  tmp_histos = NULL;
 
   // Color Cache parameters.
-  VP8LWriteBits(bw, 1, use_color_cache);
-  if (use_color_cache) {
-    VP8LWriteBits(bw, 4, cache_bits);
+  if (*cache_bits > 0) {
+    VP8LPutBits(bw, 1, 1);
+    VP8LPutBits(bw, *cache_bits, 4);
+  } else {
+    VP8LPutBits(bw, 0, 1);
   }
 
   // Huffman image + meta huffman.
   {
     const int write_histogram_image = (histogram_image_size > 1);
-    VP8LWriteBits(bw, 1, write_histogram_image);
+    VP8LPutBits(bw, write_histogram_image, 1);
     if (write_histogram_image) {
       uint32_t* const histogram_argb =
-          (uint32_t*)WebPSafeMalloc((uint64_t)histogram_image_xysize,
+          (uint32_t*)WebPSafeMalloc(histogram_image_xysize,
                                     sizeof(*histogram_argb));
       int max_index = 0;
       uint32_t i;
-      if (histogram_argb == NULL) goto Error;
+      if (histogram_argb == NULL) {
+        err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+        goto Error;
+      }
       for (i = 0; i < histogram_image_xysize; ++i) {
-        const int index = histogram_symbols[i] & 0xffff;
-        histogram_argb[i] = 0xff000000 | (index << 8);
-        if (index >= max_index) {
-          max_index = index + 1;
+        const int symbol_index = histogram_symbols[i] & 0xffff;
+        histogram_argb[i] = (symbol_index << 8);
+        if (symbol_index >= max_index) {
+          max_index = symbol_index + 1;
         }
       }
       histogram_image_size = max_index;
 
-      VP8LWriteBits(bw, 3, histogram_bits - 2);
-      ok = EncodeImageNoHuffman(bw, histogram_argb,
-                                VP8LSubSampleSize(width, histogram_bits),
-                                VP8LSubSampleSize(height, histogram_bits),
-                                quality);
-      free(histogram_argb);
-      if (!ok) goto Error;
+      VP8LPutBits(bw, histogram_bits - 2, 3);
+      err = EncodeImageNoHuffman(bw, histogram_argb, hash_chain, refs_array,
+                                 VP8LSubSampleSize(width, histogram_bits),
+                                 VP8LSubSampleSize(height, histogram_bits),
+                                 quality);
+      WebPSafeFree(histogram_argb);
+      if (err != VP8_ENC_OK) goto Error;
     }
   }
 
   // Store Huffman codes.
   {
     int i;
+    int max_tokens = 0;
+    huff_tree = (HuffmanTree*)WebPSafeMalloc(3ULL * CODE_LENGTH_CODES,
+                                             sizeof(*huff_tree));
+    if (huff_tree == NULL) {
+      err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+      goto Error;
+    }
+    // Find maximum number of symbols for the huffman tree-set.
     for (i = 0; i < 5 * histogram_image_size; ++i) {
       HuffmanTreeCode* const codes = &huffman_codes[i];
-      if (!StoreHuffmanCode(bw, codes)) goto Error;
+      if (max_tokens < codes->num_symbols) {
+        max_tokens = codes->num_symbols;
+      }
+    }
+    tokens = (HuffmanTreeToken*)WebPSafeMalloc(max_tokens,
+                                               sizeof(*tokens));
+    if (tokens == NULL) {
+      err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+      goto Error;
+    }
+    for (i = 0; i < 5 * histogram_image_size; ++i) {
+      HuffmanTreeCode* const codes = &huffman_codes[i];
+      StoreHuffmanCode(bw, huff_tree, tokens, codes);
       ClearHuffmanTreeIfOnlyOneSymbol(codes);
     }
   }
-  // Free combined histograms.
-  free(histogram_image);
-  histogram_image = NULL;
 
+  *hdr_size = (int)(VP8LBitWriterNumBytes(bw) - init_byte_position);
   // Store actual literals.
-  StoreImageToBitMask(bw, width, histogram_bits, &refs,
-                      histogram_symbols, huffman_codes);
-  ok = 1;
+  err = StoreImageToBitMask(bw, width, histogram_bits, &refs,
+                            histogram_symbols, huffman_codes);
+  *data_size =
+        (int)(VP8LBitWriterNumBytes(bw) - init_byte_position - *hdr_size);
 
  Error:
-  if (!ok) free(histogram_image);
-
-  VP8LClearBackwardRefs(&refs);
+  WebPSafeFree(tokens);
+  WebPSafeFree(huff_tree);
+  VP8LFreeHistogramSet(histogram_image);
+  VP8LFreeHistogramSet(tmp_histos);
+  VP8LBackwardRefsClear(&refs);
   if (huffman_codes != NULL) {
-    free(huffman_codes->codes);
-    free(huffman_codes);
+    WebPSafeFree(huffman_codes->codes);
+    WebPSafeFree(huffman_codes);
   }
-  free(histogram_symbols);
-  return ok;
+  WebPSafeFree(histogram_symbols);
+  return err;
 }
 
 // -----------------------------------------------------------------------------
 // Transforms
 
-// Check if it would be a good idea to subtract green from red and blue. We
-// only impact entropy in red/blue components, don't bother to look at others.
-static int EvalAndApplySubtractGreen(VP8LEncoder* const enc,
-                                     int width, int height,
-                                     VP8LBitWriter* const bw) {
-  if (!enc->use_palette_) {
-    int i;
-    const uint32_t* const argb = enc->argb_;
-    double bit_cost_before, bit_cost_after;
-    VP8LHistogram* const histo = (VP8LHistogram*)malloc(sizeof(*histo));
-    if (histo == NULL) return 0;
-
-    VP8LHistogramInit(histo, 1);
-    for (i = 0; i < width * height; ++i) {
-      const uint32_t c = argb[i];
-      ++histo->red_[(c >> 16) & 0xff];
-      ++histo->blue_[(c >> 0) & 0xff];
-    }
-    bit_cost_before = VP8LHistogramEstimateBits(histo);
-
-    VP8LHistogramInit(histo, 1);
-    for (i = 0; i < width * height; ++i) {
-      const uint32_t c = argb[i];
-      const int green = (c >> 8) & 0xff;
-      ++histo->red_[((c >> 16) - green) & 0xff];
-      ++histo->blue_[((c >> 0) - green) & 0xff];
-    }
-    bit_cost_after = VP8LHistogramEstimateBits(histo);
-    free(histo);
-
-    // Check if subtracting green yields low entropy.
-    enc->use_subtract_green_ = (bit_cost_after < bit_cost_before);
-    if (enc->use_subtract_green_) {
-      VP8LWriteBits(bw, 1, TRANSFORM_PRESENT);
-      VP8LWriteBits(bw, 2, SUBTRACT_GREEN);
-      VP8LSubtractGreenFromBlueAndRed(enc->argb_, width * height);
-    }
-  }
-  return 1;
+static void ApplySubtractGreen(VP8LEncoder* const enc, int width, int height,
+                               VP8LBitWriter* const bw) {
+  VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
+  VP8LPutBits(bw, SUBTRACT_GREEN, 2);
+  VP8LSubtractGreenFromBlueAndRed(enc->argb_, width * height);
 }
 
-static int ApplyPredictFilter(const VP8LEncoder* const enc,
-                              int width, int height, int quality,
-                              VP8LBitWriter* const bw) {
+static WebPEncodingError ApplyPredictFilter(const VP8LEncoder* const enc,
+                                            int width, int height,
+                                            int quality, int low_effort,
+                                            VP8LBitWriter* const bw) {
   const int pred_bits = enc->transform_bits_;
   const int transform_width = VP8LSubSampleSize(width, pred_bits);
   const int transform_height = VP8LSubSampleSize(height, pred_bits);
 
-  VP8LResidualImage(width, height, pred_bits, enc->argb_, enc->argb_scratch_,
-                    enc->transform_data_);
-  VP8LWriteBits(bw, 1, TRANSFORM_PRESENT);
-  VP8LWriteBits(bw, 2, PREDICTOR_TRANSFORM);
+  VP8LResidualImage(width, height, pred_bits, low_effort, enc->argb_,
+                    enc->argb_scratch_, enc->transform_data_);
+  VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
+  VP8LPutBits(bw, PREDICTOR_TRANSFORM, 2);
   assert(pred_bits >= 2);
-  VP8LWriteBits(bw, 3, pred_bits - 2);
-  if (!EncodeImageNoHuffman(bw, enc->transform_data_,
-                            transform_width, transform_height, quality)) {
-    return 0;
-  }
-  return 1;
+  VP8LPutBits(bw, pred_bits - 2, 3);
+  return EncodeImageNoHuffman(bw, enc->transform_data_,
+                              (VP8LHashChain*)&enc->hash_chain_,
+                              (VP8LBackwardRefs*)enc->refs_,  // cast const away
+                              transform_width, transform_height,
+                              quality);
 }
 
-static int ApplyCrossColorFilter(const VP8LEncoder* const enc,
-                                 int width, int height, int quality,
-                                 VP8LBitWriter* const bw) {
+static WebPEncodingError ApplyCrossColorFilter(const VP8LEncoder* const enc,
+                                               int width, int height,
+                                               int quality,
+                                               VP8LBitWriter* const bw) {
   const int ccolor_transform_bits = enc->transform_bits_;
   const int transform_width = VP8LSubSampleSize(width, ccolor_transform_bits);
   const int transform_height = VP8LSubSampleSize(height, ccolor_transform_bits);
-  const int step = (quality == 0) ? 32 : 8;
 
-  VP8LColorSpaceTransform(width, height, ccolor_transform_bits, step,
+  VP8LColorSpaceTransform(width, height, ccolor_transform_bits, quality,
                           enc->argb_, enc->transform_data_);
-  VP8LWriteBits(bw, 1, TRANSFORM_PRESENT);
-  VP8LWriteBits(bw, 2, CROSS_COLOR_TRANSFORM);
+  VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
+  VP8LPutBits(bw, CROSS_COLOR_TRANSFORM, 2);
   assert(ccolor_transform_bits >= 2);
-  VP8LWriteBits(bw, 3, ccolor_transform_bits - 2);
-  if (!EncodeImageNoHuffman(bw, enc->transform_data_,
-                            transform_width, transform_height, quality)) {
-    return 0;
-  }
-  return 1;
+  VP8LPutBits(bw, ccolor_transform_bits - 2, 3);
+  return EncodeImageNoHuffman(bw, enc->transform_data_,
+                              (VP8LHashChain*)&enc->hash_chain_,
+                              (VP8LBackwardRefs*)enc->refs_,  // cast const away
+                              transform_width, transform_height,
+                              quality);
 }
 
 // -----------------------------------------------------------------------------
 
-static void PutLE32(uint8_t* const data, uint32_t val) {
-  data[0] = (val >>  0) & 0xff;
-  data[1] = (val >>  8) & 0xff;
-  data[2] = (val >> 16) & 0xff;
-  data[3] = (val >> 24) & 0xff;
-}
-
 static WebPEncodingError WriteRiffHeader(const WebPPicture* const pic,
                                          size_t riff_size, size_t vp8l_size) {
   uint8_t riff[RIFF_HEADER_SIZE + CHUNK_HEADER_SIZE + VP8L_SIGNATURE_SIZE] = {
@@ -733,14 +1067,14 @@ static int WriteImageSize(const WebPPicture* const pic,
   const int height = pic->height - 1;
   assert(width < WEBP_MAX_DIMENSION && height < WEBP_MAX_DIMENSION);
 
-  VP8LWriteBits(bw, VP8L_IMAGE_SIZE_BITS, width);
-  VP8LWriteBits(bw, VP8L_IMAGE_SIZE_BITS, height);
+  VP8LPutBits(bw, width, VP8L_IMAGE_SIZE_BITS);
+  VP8LPutBits(bw, height, VP8L_IMAGE_SIZE_BITS);
   return !bw->error_;
 }
 
 static int WriteRealAlphaAndVersion(VP8LBitWriter* const bw, int has_alpha) {
-  VP8LWriteBits(bw, 1, has_alpha);
-  VP8LWriteBits(bw, VP8L_VERSION_BITS, VP8L_VERSION);
+  VP8LPutBits(bw, has_alpha, 1);
+  VP8LPutBits(bw, VP8L_VERSION, VP8L_VERSION_BITS);
   return !bw->error_;
 }
 
@@ -780,166 +1114,261 @@ static WebPEncodingError WriteImage(const WebPPicture* const pic,
 
 // Allocates the memory for argb (W x H) buffer, 2 rows of context for
 // prediction and transform data.
+// Flags influencing the memory allocated:
+//  enc->transform_bits_
+//  enc->use_predict_, enc->use_cross_color_
 static WebPEncodingError AllocateTransformBuffer(VP8LEncoder* const enc,
                                                  int width, int height) {
   WebPEncodingError err = VP8_ENC_OK;
-  const int tile_size = 1 << enc->transform_bits_;
-  const uint64_t image_size = width * height;
-  const uint64_t argb_scratch_size = tile_size * width + width;
-  const uint64_t transform_data_size =
-      (uint64_t)VP8LSubSampleSize(width, enc->transform_bits_) *
-      (uint64_t)VP8LSubSampleSize(height, enc->transform_bits_);
-  const uint64_t total_size =
-      image_size + argb_scratch_size + transform_data_size;
-  uint32_t* mem = (uint32_t*)WebPSafeMalloc(total_size, sizeof(*mem));
-  if (mem == NULL) {
-    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
-    goto Error;
+  if (enc->argb_ == NULL) {
+    const int tile_size = 1 << enc->transform_bits_;
+    const uint64_t image_size = width * height;
+    // Ensure enough size for tiles, as well as for two scanlines and two
+    // extra pixels for CopyImageWithPrediction.
+    const uint64_t argb_scratch_size =
+        enc->use_predict_ ? tile_size * width + width + 2 : 0;
+    const int transform_data_size =
+        (enc->use_predict_ || enc->use_cross_color_)
+            ? VP8LSubSampleSize(width, enc->transform_bits_) *
+              VP8LSubSampleSize(height, enc->transform_bits_)
+            : 0;
+    const uint64_t total_size =
+        image_size + WEBP_ALIGN_CST +
+        argb_scratch_size + WEBP_ALIGN_CST +
+        (uint64_t)transform_data_size;
+    uint32_t* mem = (uint32_t*)WebPSafeMalloc(total_size, sizeof(*mem));
+    if (mem == NULL) {
+      err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+      goto Error;
+    }
+    enc->argb_ = mem;
+    mem = (uint32_t*)WEBP_ALIGN(mem + image_size);
+    enc->argb_scratch_ = mem;
+    mem = (uint32_t*)WEBP_ALIGN(mem + argb_scratch_size);
+    enc->transform_data_ = mem;
+    enc->current_width_ = width;
   }
-  enc->argb_ = mem;
-  mem += image_size;
-  enc->argb_scratch_ = mem;
-  mem += argb_scratch_size;
-  enc->transform_data_ = mem;
-  enc->current_width_ = width;
-
  Error:
   return err;
 }
 
-// Bundles multiple (2, 4 or 8) pixels into a single pixel.
-// Returns the new xsize.
-static void BundleColorMap(const WebPPicture* const pic,
-                           int xbits, uint32_t* bundled_argb, int xs) {
-  int y;
-  const int bit_depth = 1 << (3 - xbits);
-  uint32_t code = 0;
-  const uint32_t* argb = pic->argb;
-  const int width = pic->width;
-  const int height = pic->height;
+static void ClearTransformBuffer(VP8LEncoder* const enc) {
+  WebPSafeFree(enc->argb_);
+  enc->argb_ = NULL;
+}
 
+static WebPEncodingError MakeInputImageCopy(VP8LEncoder* const enc) {
+  WebPEncodingError err = VP8_ENC_OK;
+  const WebPPicture* const picture = enc->pic_;
+  const int width = picture->width;
+  const int height = picture->height;
+  int y;
+  err = AllocateTransformBuffer(enc, width, height);
+  if (err != VP8_ENC_OK) return err;
   for (y = 0; y < height; ++y) {
-    int x;
-    for (x = 0; x < width; ++x) {
-      const int mask = (1 << xbits) - 1;
-      const int xsub = x & mask;
-      if (xsub == 0) {
-        code = 0;
-      }
-      // TODO(vikasa): simplify the bundling logic.
-      code |= (argb[x] & 0xff00) << (bit_depth * xsub);
-      bundled_argb[y * xs + (x >> xbits)] = 0xff000000 | code;
-    }
-    argb += pic->argb_stride;
+    memcpy(enc->argb_ + y * width,
+           picture->argb + y * picture->argb_stride,
+           width * sizeof(*enc->argb_));
   }
+  assert(enc->current_width_ == width);
+  return VP8_ENC_OK;
 }
 
-// Note: Expects "enc->palette_" to be set properly.
-// Also, "enc->palette_" will be modified after this call and should not be used
-// later.
-static WebPEncodingError ApplyPalette(VP8LBitWriter* const bw,
-                                      VP8LEncoder* const enc, int quality) {
-  WebPEncodingError err = VP8_ENC_OK;
-  int i, x, y;
-  const WebPPicture* const pic = enc->pic_;
-  uint32_t* argb = pic->argb;
-  const int width = pic->width;
-  const int height = pic->height;
-  uint32_t* const palette = enc->palette_;
-  const int palette_size = enc->palette_size_;
+// -----------------------------------------------------------------------------
 
-  // Replace each input pixel by corresponding palette index.
-  for (y = 0; y < height; ++y) {
-    for (x = 0; x < width; ++x) {
-      const uint32_t pix = argb[x];
-      for (i = 0; i < palette_size; ++i) {
+static void MapToPalette(const uint32_t palette[], int num_colors,
+                         uint32_t* const last_pix, int* const last_idx,
+                         const uint32_t* src, uint8_t* dst, int width) {
+  int x;
+  int prev_idx = *last_idx;
+  uint32_t prev_pix = *last_pix;
+  for (x = 0; x < width; ++x) {
+    const uint32_t pix = src[x];
+    if (pix != prev_pix) {
+      int i;
+      for (i = 0; i < num_colors; ++i) {
         if (pix == palette[i]) {
-          argb[x] = 0xff000000u | (i << 8);
+          prev_idx = i;
+          prev_pix = pix;
           break;
         }
       }
     }
-    argb += pic->argb_stride;
+    dst[x] = prev_idx;
   }
+  *last_idx = prev_idx;
+  *last_pix = prev_pix;
+}
 
-  // Save palette to bitstream.
-  VP8LWriteBits(bw, 1, TRANSFORM_PRESENT);
-  VP8LWriteBits(bw, 2, COLOR_INDEXING_TRANSFORM);
-  assert(palette_size >= 1);
-  VP8LWriteBits(bw, 8, palette_size - 1);
-  for (i = palette_size - 1; i >= 1; --i) {
-    palette[i] = VP8LSubPixels(palette[i], palette[i - 1]);
-  }
-  if (!EncodeImageNoHuffman(bw, palette, palette_size, 1, quality)) {
-    err = VP8_ENC_ERROR_INVALID_CONFIGURATION;
-    goto Error;
+// Remap argb values in src[] to packed palettes entries in dst[]
+// using 'row' as a temporary buffer of size 'width'.
+// We assume that all src[] values have a corresponding entry in the palette.
+// Note: src[] can be the same as dst[]
+static WebPEncodingError ApplyPalette(const uint32_t* src, uint32_t src_stride,
+                                      uint32_t* dst, uint32_t dst_stride,
+                                      const uint32_t* palette, int palette_size,
+                                      int width, int height, int xbits) {
+  // TODO(skal): this tmp buffer is not needed if VP8LBundleColorMap() can be
+  // made to work in-place.
+  uint8_t* const tmp_row = (uint8_t*)WebPSafeMalloc(width, sizeof(*tmp_row));
+  int i, x, y;
+  int use_LUT = 1;
+
+  if (tmp_row == NULL) return VP8_ENC_ERROR_OUT_OF_MEMORY;
+  for (i = 0; i < palette_size; ++i) {
+    if ((palette[i] & 0xffff00ffu) != 0) {
+      use_LUT = 0;
+      break;
+    }
   }
 
-  if (palette_size <= 16) {
-    // Image can be packed (multiple pixels per uint32_t).
-    int xbits = 1;
-    if (palette_size <= 2) {
-      xbits = 3;
-    } else if (palette_size <= 4) {
-      xbits = 2;
+  if (use_LUT) {
+    uint8_t inv_palette[MAX_PALETTE_SIZE] = { 0 };
+    for (i = 0; i < palette_size; ++i) {
+      const int color = (palette[i] >> 8) & 0xff;
+      inv_palette[color] = i;
+    }
+    for (y = 0; y < height; ++y) {
+      for (x = 0; x < width; ++x) {
+        const int color = (src[x] >> 8) & 0xff;
+        tmp_row[x] = inv_palette[color];
+      }
+      VP8LBundleColorMap(tmp_row, width, xbits, dst);
+      src += src_stride;
+      dst += dst_stride;
+    }
+  } else {
+    // Use 1 pixel cache for ARGB pixels.
+    uint32_t last_pix = palette[0];
+    int last_idx = 0;
+    for (y = 0; y < height; ++y) {
+      MapToPalette(palette, palette_size, &last_pix, &last_idx,
+                   src, tmp_row, width);
+      VP8LBundleColorMap(tmp_row, width, xbits, dst);
+      src += src_stride;
+      dst += dst_stride;
     }
-    err = AllocateTransformBuffer(enc, VP8LSubSampleSize(width, xbits), height);
-    if (err != VP8_ENC_OK) goto Error;
-    BundleColorMap(pic, xbits, enc->argb_, enc->current_width_);
   }
+  WebPSafeFree(tmp_row);
+  return VP8_ENC_OK;
+}
 
- Error:
+// Note: Expects "enc->palette_" to be set properly.
+static WebPEncodingError MapImageFromPalette(VP8LEncoder* const enc,
+                                             int in_place) {
+  WebPEncodingError err = VP8_ENC_OK;
+  const WebPPicture* const pic = enc->pic_;
+  const int width = pic->width;
+  const int height = pic->height;
+  const uint32_t* const palette = enc->palette_;
+  const uint32_t* src = in_place ? enc->argb_ : pic->argb;
+  const int src_stride = in_place ? enc->current_width_ : pic->argb_stride;
+  const int palette_size = enc->palette_size_;
+  int xbits;
+
+  // Replace each input pixel by corresponding palette index.
+  // This is done line by line.
+  if (palette_size <= 4) {
+    xbits = (palette_size <= 2) ? 3 : 2;
+  } else {
+    xbits = (palette_size <= 16) ? 1 : 0;
+  }
+
+  err = AllocateTransformBuffer(enc, VP8LSubSampleSize(width, xbits), height);
+  if (err != VP8_ENC_OK) return err;
+
+  err = ApplyPalette(src, src_stride,
+                     enc->argb_, enc->current_width_,
+                     palette, palette_size, width, height, xbits);
   return err;
 }
 
-// -----------------------------------------------------------------------------
+// Save palette_[] to bitstream.
+static WebPEncodingError EncodePalette(VP8LBitWriter* const bw,
+                                       VP8LEncoder* const enc) {
+  int i;
+  uint32_t tmp_palette[MAX_PALETTE_SIZE];
+  const int palette_size = enc->palette_size_;
+  const uint32_t* const palette = enc->palette_;
+  VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
+  VP8LPutBits(bw, COLOR_INDEXING_TRANSFORM, 2);
+  assert(palette_size >= 1 && palette_size <= MAX_PALETTE_SIZE);
+  VP8LPutBits(bw, palette_size - 1, 8);
+  for (i = palette_size - 1; i >= 1; --i) {
+    tmp_palette[i] = VP8LSubPixels(palette[i], palette[i - 1]);
+  }
+  tmp_palette[0] = palette[0];
+  return EncodeImageNoHuffman(bw, tmp_palette, &enc->hash_chain_, enc->refs_,
+                              palette_size, 1, 20 /* quality */);
+}
 
-static int GetHistoBits(const WebPConfig* const config,
-                        const WebPPicture* const pic) {
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+
+static WebPEncodingError EncodeDeltaPalettePredictorImage(
+    VP8LBitWriter* const bw, VP8LEncoder* const enc, int quality) {
+  const WebPPicture* const pic = enc->pic_;
   const int width = pic->width;
   const int height = pic->height;
-  const size_t hist_size = sizeof(VP8LHistogram);
-  // Make tile size a function of encoding method (Range: 0 to 6).
-  int histo_bits = 7 - config->method;
-  while (1) {
-    const size_t huff_image_size = VP8LSubSampleSize(width, histo_bits) *
-                                   VP8LSubSampleSize(height, histo_bits) *
-                                   hist_size;
-    if (huff_image_size <= MAX_HUFF_IMAGE_SIZE) break;
-    ++histo_bits;
+
+  const int pred_bits = 5;
+  const int transform_width = VP8LSubSampleSize(width, pred_bits);
+  const int transform_height = VP8LSubSampleSize(height, pred_bits);
+  const int pred = 7;   // default is Predictor7 (Top/Left Average)
+  const int tiles_per_row = VP8LSubSampleSize(width, pred_bits);
+  const int tiles_per_col = VP8LSubSampleSize(height, pred_bits);
+  uint32_t* predictors;
+  int tile_x, tile_y;
+  WebPEncodingError err = VP8_ENC_OK;
+
+  predictors = (uint32_t*)WebPSafeMalloc(tiles_per_col * tiles_per_row,
+                                         sizeof(*predictors));
+  if (predictors == NULL) return VP8_ENC_ERROR_OUT_OF_MEMORY;
+
+  for (tile_y = 0; tile_y < tiles_per_col; ++tile_y) {
+    for (tile_x = 0; tile_x < tiles_per_row; ++tile_x) {
+      predictors[tile_y * tiles_per_row + tile_x] = 0xff000000u | (pred << 8);
+    }
   }
-  return (histo_bits < MIN_HUFFMAN_BITS) ? MIN_HUFFMAN_BITS :
-         (histo_bits > MAX_HUFFMAN_BITS) ? MAX_HUFFMAN_BITS : histo_bits;
-}
 
-static void InitEncParams(VP8LEncoder* const enc) {
-  const WebPConfig* const config = enc->config_;
-  const WebPPicture* const picture = enc->pic_;
-  const int method = config->method;
-  const float quality = config->quality;
-  enc->transform_bits_ = (method < 4) ? 5 : (method > 4) ? 3 : 4;
-  enc->histo_bits_ = GetHistoBits(config, picture);
-  enc->cache_bits_ = (quality <= 25.f) ? 0 : 7;
+  VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
+  VP8LPutBits(bw, PREDICTOR_TRANSFORM, 2);
+  VP8LPutBits(bw, pred_bits - 2, 3);
+  err = EncodeImageNoHuffman(bw, predictors, &enc->hash_chain_,
+                             (VP8LBackwardRefs*)enc->refs_,  // cast const away
+                             transform_width, transform_height,
+                             quality);
+  WebPSafeFree(predictors);
+  return err;
 }
 
+#endif // WEBP_EXPERIMENTAL_FEATURES
+
 // -----------------------------------------------------------------------------
 // VP8LEncoder
 
 static VP8LEncoder* VP8LEncoderNew(const WebPConfig* const config,
                                    const WebPPicture* const picture) {
-  VP8LEncoder* const enc = (VP8LEncoder*)calloc(1, sizeof(*enc));
+  VP8LEncoder* const enc = (VP8LEncoder*)WebPSafeCalloc(1ULL, sizeof(*enc));
   if (enc == NULL) {
     WebPEncodingSetError(picture, VP8_ENC_ERROR_OUT_OF_MEMORY);
     return NULL;
   }
   enc->config_ = config;
   enc->pic_ = picture;
+
+  VP8LEncDspInit();
+
   return enc;
 }
 
 static void VP8LEncoderDelete(VP8LEncoder* enc) {
-  free(enc->argb_);
-  free(enc);
+  if (enc != NULL) {
+    VP8LHashChainClear(&enc->hash_chain_);
+    VP8LBackwardRefsClear(&enc->refs_[0]);
+    VP8LBackwardRefsClear(&enc->refs_[1]);
+    ClearTransformBuffer(enc);
+    WebPSafeFree(enc);
+  }
 }
 
 // -----------------------------------------------------------------------------
@@ -950,89 +1379,102 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
                                    VP8LBitWriter* const bw) {
   WebPEncodingError err = VP8_ENC_OK;
   const int quality = (int)config->quality;
+  const int low_effort = (config->method == 0);
   const int width = picture->width;
   const int height = picture->height;
   VP8LEncoder* const enc = VP8LEncoderNew(config, picture);
   const size_t byte_position = VP8LBitWriterNumBytes(bw);
+  int use_near_lossless = 0;
+  int hdr_size = 0;
+  int data_size = 0;
+  int use_delta_palettization = 0;
 
   if (enc == NULL) {
     err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
 
-  InitEncParams(enc);
-
   // ---------------------------------------------------------------------------
   // Analyze image (entropy, num_palettes etc)
 
-  if (!VP8LEncAnalyze(enc, config->image_hint)) {
+  if (!AnalyzeAndInit(enc)) {
     err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
 
-  if (enc->use_palette_) {
-    err = ApplyPalette(bw, enc, quality);
-    if (err != VP8_ENC_OK) goto Error;
-    // Color cache is disabled for palette.
-    enc->cache_bits_ = 0;
+  // Apply near-lossless preprocessing.
+  use_near_lossless = !enc->use_palette_ && (config->near_lossless < 100);
+  if (use_near_lossless) {
+    if (!VP8ApplyNearLossless(width, height, picture->argb,
+                              config->near_lossless)) {
+      err = VP8_ENC_ERROR_OUT_OF_MEMORY;
+      goto Error;
+    }
   }
 
-  // In case image is not packed.
-  if (enc->argb_ == NULL) {
-    int y;
-    err = AllocateTransformBuffer(enc, width, height);
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+  if (config->delta_palettization) {
+    enc->use_predict_ = 1;
+    enc->use_cross_color_ = 0;
+    enc->use_subtract_green_ = 0;
+    enc->use_palette_ = 1;
+    err = MakeInputImageCopy(enc);
     if (err != VP8_ENC_OK) goto Error;
-    for (y = 0; y < height; ++y) {
-      memcpy(enc->argb_ + y * width,
-             picture->argb + y * picture->argb_stride,
-             width * sizeof(*enc->argb_));
+    err = WebPSearchOptimalDeltaPalette(enc);
+    if (err != VP8_ENC_OK) goto Error;
+    if (enc->use_palette_) {
+      err = AllocateTransformBuffer(enc, width, height);
+      if (err != VP8_ENC_OK) goto Error;
+      err = EncodeDeltaPalettePredictorImage(bw, enc, quality);
+      if (err != VP8_ENC_OK) goto Error;
+      use_delta_palettization = 1;
     }
-    enc->current_width_ = width;
   }
+#endif  // WEBP_EXPERIMENTAL_FEATURES
 
-  // ---------------------------------------------------------------------------
-  // Apply transforms and write transform data.
-
-  if (!EvalAndApplySubtractGreen(enc, enc->current_width_, height, bw)) {
-    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
-    goto Error;
+  // Encode palette
+  if (enc->use_palette_) {
+    err = EncodePalette(bw, enc);
+    if (err != VP8_ENC_OK) goto Error;
+    err = MapImageFromPalette(enc, use_delta_palettization);
+    if (err != VP8_ENC_OK) goto Error;
   }
-
-  if (enc->use_predict_) {
-    if (!ApplyPredictFilter(enc, enc->current_width_, height, quality, bw)) {
-      err = VP8_ENC_ERROR_INVALID_CONFIGURATION;
-      goto Error;
+  if (!use_delta_palettization) {
+    // In case image is not packed.
+    if (enc->argb_ == NULL) {
+      err = MakeInputImageCopy(enc);
+      if (err != VP8_ENC_OK) goto Error;
     }
-  }
 
-  if (enc->use_cross_color_) {
-    if (!ApplyCrossColorFilter(enc, enc->current_width_, height, quality, bw)) {
-      err = VP8_ENC_ERROR_INVALID_CONFIGURATION;
-      goto Error;
-    }
-  }
+    // -------------------------------------------------------------------------
+    // Apply transforms and write transform data.
 
-  VP8LWriteBits(bw, 1, !TRANSFORM_PRESENT);  // No more transforms.
+    if (enc->use_subtract_green_) {
+      ApplySubtractGreen(enc, enc->current_width_, height, bw);
+    }
 
-  // ---------------------------------------------------------------------------
-  // Estimate the color cache size.
+    if (enc->use_predict_) {
+      err = ApplyPredictFilter(enc, enc->current_width_, height, quality,
+                               low_effort, bw);
+      if (err != VP8_ENC_OK) goto Error;
+    }
 
-  if (enc->cache_bits_ > 0) {
-    if (!VP8LCalculateEstimateForCacheSize(enc->argb_, enc->current_width_,
-                                           height, &enc->cache_bits_)) {
-      err = VP8_ENC_ERROR_INVALID_CONFIGURATION;
-      goto Error;
+    if (enc->use_cross_color_) {
+      err = ApplyCrossColorFilter(enc, enc->current_width_,
+                                  height, quality, bw);
+      if (err != VP8_ENC_OK) goto Error;
     }
   }
 
+  VP8LPutBits(bw, !TRANSFORM_PRESENT, 1);  // No more transforms.
+
   // ---------------------------------------------------------------------------
   // Encode and write the transformed image.
-
-  if (!EncodeImageInternal(bw, enc->argb_, enc->current_width_, height,
-                           quality, enc->cache_bits_, enc->histo_bits_)) {
-    err = VP8_ENC_ERROR_OUT_OF_MEMORY;
-    goto Error;
-  }
+  err = EncodeImageInternal(bw, enc->argb_, &enc->hash_chain_, enc->refs_,
+                            enc->current_width_, height, quality, low_effort,
+                            &enc->cache_bits_, enc->histo_bits_, byte_position,
+                            &hdr_size, &data_size);
+  if (err != VP8_ENC_OK) goto Error;
 
   if (picture->stats != NULL) {
     WebPAuxStats* const stats = picture->stats;
@@ -1046,6 +1488,8 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
     stats->cache_bits = enc->cache_bits_;
     stats->palette_size = enc->palette_size_;
     stats->lossless_size = (int)(VP8LBitWriterNumBytes(bw) - byte_position);
+    stats->lossless_hdr_size = hdr_size;
+    stats->lossless_data_size = data_size;
   }
 
  Error:
@@ -1059,6 +1503,7 @@ int VP8LEncodeImage(const WebPConfig* const config,
   int has_alpha;
   size_t coded_size;
   int percent = 0;
+  int initial_size;
   WebPEncodingError err = VP8_ENC_OK;
   VP8LBitWriter bw;
 
@@ -1072,7 +1517,11 @@ int VP8LEncodeImage(const WebPConfig* const config,
 
   width = picture->width;
   height = picture->height;
-  if (!VP8LBitWriterInit(&bw, (width * height) >> 1)) {
+  // Initialize BitWriter with size corresponding to 16 bpp to photo images and
+  // 8 bpp for graphical images.
+  initial_size = (config->image_hint == WEBP_HINT_GRAPH) ?
+      width * height : width * height * 2;
+  if (!VP8LBitWriterInit(&bw, initial_size)) {
     err = VP8_ENC_ERROR_OUT_OF_MEMORY;
     goto Error;
   }
@@ -1135,7 +1584,7 @@ int VP8LEncodeImage(const WebPConfig* const config,
 
  Error:
   if (bw.error_) err = VP8_ENC_ERROR_OUT_OF_MEMORY;
-  VP8LBitWriterDestroy(&bw);
+  VP8LBitWriterWipeOut(&bw);
   if (err != VP8_ENC_OK) {
     WebPEncodingSetError(picture, err);
     return 0;
@@ -1144,7 +1593,3 @@ int VP8LEncodeImage(const WebPConfig* const config,
 }
 
 //------------------------------------------------------------------------------
-
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif
diff --git a/drivers/webp/enc/vp8li.h b/drivers/webp/enc/vp8li.h
index bb111aec33..6b6db127db 100644
--- a/drivers/webp/enc/vp8li.h
+++ b/drivers/webp/enc/vp8li.h
@@ -1,8 +1,10 @@
 // Copyright 2012 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Lossless encoder: internal header.
@@ -12,12 +14,13 @@
 #ifndef WEBP_ENC_VP8LI_H_
 #define WEBP_ENC_VP8LI_H_
 
+#include "./backward_references.h"
 #include "./histogram.h"
 #include "../utils/bit_writer.h"
-#include "../encode.h"
-#include "../format_constants.h"
+#include "../webp/encode.h"
+#include "../webp/format_constants.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -43,6 +46,12 @@ typedef struct {
   int use_palette_;
   int palette_size_;
   uint32_t palette_[MAX_PALETTE_SIZE];
+
+  // Some 'scratch' (potentially large) objects.
+  struct VP8LBackwardRefs refs_[2];  // Backward Refs array corresponding to
+                                     // LZ77 & RLE coding.
+  VP8LHashChain hash_chain_;         // HashChain data for constructing
+                                     // backward references.
 } VP8LEncoder;
 
 //------------------------------------------------------------------------------
@@ -61,7 +70,7 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/drivers/webp/enc/webpenc.c b/drivers/webp/enc/webpenc.c
index 3c275589fc..8ced07a2a3 100644
--- a/drivers/webp/enc/webpenc.c
+++ b/drivers/webp/enc/webpenc.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // WebP encoder: main entry point
@@ -14,16 +16,13 @@
 #include <string.h>
 #include <math.h>
 
+#include "./cost.h"
 #include "./vp8enci.h"
 #include "./vp8li.h"
 #include "../utils/utils.h"
 
 // #define PRINT_MEMORY_INFO
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 #ifdef PRINT_MEMORY_INFO
 #include <stdio.h>
 #endif
@@ -35,43 +34,18 @@ int WebPGetEncoderVersion(void) {
 }
 
 //------------------------------------------------------------------------------
-// WebPPicture
-//------------------------------------------------------------------------------
-
-static int DummyWriter(const uint8_t* data, size_t data_size,
-                       const WebPPicture* const picture) {
-  // The following are to prevent 'unused variable' error message.
-  (void)data;
-  (void)data_size;
-  (void)picture;
-  return 1;
-}
-
-int WebPPictureInitInternal(WebPPicture* picture, int version) {
-  if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_ENCODER_ABI_VERSION)) {
-    return 0;   // caller/system version mismatch!
-  }
-  if (picture != NULL) {
-    memset(picture, 0, sizeof(*picture));
-    picture->writer = DummyWriter;
-    WebPEncodingSetError(picture, VP8_ENC_OK);
-  }
-  return 1;
-}
-
-//------------------------------------------------------------------------------
 // VP8Encoder
 //------------------------------------------------------------------------------
 
 static void ResetSegmentHeader(VP8Encoder* const enc) {
-  VP8SegmentHeader* const hdr = &enc->segment_hdr_;
+  VP8EncSegmentHeader* const hdr = &enc->segment_hdr_;
   hdr->num_segments_ = enc->config_->segments;
   hdr->update_map_  = (hdr->num_segments_ > 1);
   hdr->size_ = 0;
 }
 
 static void ResetFilterHeader(VP8Encoder* const enc) {
-  VP8FilterHeader* const hdr = &enc->filter_hdr_;
+  VP8EncFilterHeader* const hdr = &enc->filter_hdr_;
   hdr->simple_ = 1;
   hdr->level_ = 0;
   hdr->sharpness_ = 0;
@@ -93,56 +67,73 @@ static void ResetBoundaryPredictions(VP8Encoder* const enc) {
   enc->nz_[-1] = 0;   // constant
 }
 
-// Map configured quality level to coding tools used.
-//-------------+---+---+---+---+---+---+
-//   Quality   | 0 | 1 | 2 | 3 | 4 | 5 +
-//-------------+---+---+---+---+---+---+
-// dynamic prob| ~ | x | x | x | x | x |
-//-------------+---+---+---+---+---+---+
-// rd-opt modes|   |   | x | x | x | x |
-//-------------+---+---+---+---+---+---+
-// fast i4/i16 | x | x |   |   |   |   |
-//-------------+---+---+---+---+---+---+
-// rd-opt i4/16|   |   | x | x | x | x |
-//-------------+---+---+---+---+---+---+
-// Trellis     |   | x |   |   | x | x |
-//-------------+---+---+---+---+---+---+
-// full-SNS    |   |   |   |   |   | x |
-//-------------+---+---+---+---+---+---+
+// Mapping from config->method_ to coding tools used.
+//-------------------+---+---+---+---+---+---+---+
+//   Method          | 0 | 1 | 2 | 3 |(4)| 5 | 6 |
+//-------------------+---+---+---+---+---+---+---+
+// fast probe        | x |   |   | x |   |   |   |
+//-------------------+---+---+---+---+---+---+---+
+// dynamic proba     | ~ | x | x | x | x | x | x |
+//-------------------+---+---+---+---+---+---+---+
+// fast mode analysis|   |   |   |   | x | x | x |
+//-------------------+---+---+---+---+---+---+---+
+// basic rd-opt      |   |   |   | x | x | x | x |
+//-------------------+---+---+---+---+---+---+---+
+// disto-score i4/16 |   |   | x |   |   |   |   |
+//-------------------+---+---+---+---+---+---+---+
+// rd-opt i4/16      |   |   | ~ | x | x | x | x |
+//-------------------+---+---+---+---+---+---+---+
+// token buffer (opt)|   |   |   | x | x | x | x |
+//-------------------+---+---+---+---+---+---+---+
+// Trellis           |   |   |   |   |   | x |Ful|
+//-------------------+---+---+---+---+---+---+---+
+// full-SNS          |   |   |   |   | x | x | x |
+//-------------------+---+---+---+---+---+---+---+
 
 static void MapConfigToTools(VP8Encoder* const enc) {
-  const int method = enc->config_->method;
-  const int limit = 100 - enc->config_->partition_limit;
+  const WebPConfig* const config = enc->config_;
+  const int method = config->method;
+  const int limit = 100 - config->partition_limit;
   enc->method_ = method;
-  enc->rd_opt_level_ = (method >= 6) ? 3
-                     : (method >= 5) ? 2
-                     : (method >= 3) ? 1
-                     : 0;
+  enc->rd_opt_level_ = (method >= 6) ? RD_OPT_TRELLIS_ALL
+                     : (method >= 5) ? RD_OPT_TRELLIS
+                     : (method >= 3) ? RD_OPT_BASIC
+                     : RD_OPT_NONE;
   enc->max_i4_header_bits_ =
       256 * 16 * 16 *                 // upper bound: up to 16bit per 4x4 block
       (limit * limit) / (100 * 100);  // ... modulated with a quadratic curve.
+
+  enc->thread_level_ = config->thread_level;
+
+  enc->do_search_ = (config->target_size > 0 || config->target_PSNR > 0);
+  if (!config->low_memory) {
+#if !defined(DISABLE_TOKEN_BUFFER)
+    enc->use_tokens_ = (enc->rd_opt_level_ >= RD_OPT_BASIC);  // need rd stats
+#endif
+    if (enc->use_tokens_) {
+      enc->num_parts_ = 1;   // doesn't work with multi-partition
+    }
+  }
 }
 
 // Memory scaling with dimensions:
 //  memory (bytes) ~= 2.25 * w + 0.0625 * w * h
 //
-// Typical memory footprint (768x510 picture)
-// Memory used:
-//              encoder: 33919
-//          block cache: 2880
-//                 info: 3072
-//                preds: 24897
-//          top samples: 1623
-//             non-zero: 196
-//             lf-stats: 2048
-//                total: 68635
-// Transcient object sizes:
-//       VP8EncIterator: 352
-//         VP8ModeScore: 912
-//       VP8SegmentInfo: 532
-//             VP8Proba: 31032
+// Typical memory footprint (614x440 picture)
+//              encoder: 22111
+//                 info: 4368
+//                preds: 17741
+//          top samples: 1263
+//             non-zero: 175
+//             lf-stats: 0
+//                total: 45658
+// Transient object sizes:
+//       VP8EncIterator: 3360
+//         VP8ModeScore: 872
+//       VP8SegmentInfo: 732
+//          VP8EncProba: 18352
 //              LFStats: 2048
-// Picture size (yuv): 589824
+// Picture size (yuv): 419328
 
 static VP8Encoder* InitVP8Encoder(const WebPConfig* const config,
                                   WebPPicture* const picture) {
@@ -154,20 +145,16 @@ static VP8Encoder* InitVP8Encoder(const WebPConfig* const config,
   const int preds_h = 4 * mb_h + 1;
   const size_t preds_size = preds_w * preds_h * sizeof(uint8_t);
   const int top_stride = mb_w * 16;
-  const size_t nz_size = (mb_w + 1) * sizeof(uint32_t);
-  const size_t cache_size = (3 * YUV_SIZE + PRED_SIZE) * sizeof(uint8_t);
+  const size_t nz_size = (mb_w + 1) * sizeof(uint32_t) + WEBP_ALIGN_CST;
   const size_t info_size = mb_w * mb_h * sizeof(VP8MBInfo);
-  const size_t samples_size = (2 * top_stride +         // top-luma/u/v
-                               16 + 16 + 16 + 8 + 1 +   // left y/u/v
-                               2 * ALIGN_CST)           // align all
-                               * sizeof(uint8_t);
+  const size_t samples_size = 2 * top_stride * sizeof(uint8_t)  // top-luma/u/v
+                            + WEBP_ALIGN_CST;                   // align all
   const size_t lf_stats_size =
-      config->autofilter ? sizeof(LFStats) + ALIGN_CST : 0;
+      config->autofilter ? sizeof(LFStats) + WEBP_ALIGN_CST : 0;
   VP8Encoder* enc;
   uint8_t* mem;
   const uint64_t size = (uint64_t)sizeof(VP8Encoder)   // main struct
-                      + ALIGN_CST                      // cache alignment
-                      + cache_size                     // working caches
+                      + WEBP_ALIGN_CST                 // cache alignment
                       + info_size                      // modes info
                       + preds_size                     // prediction modes
                       + samples_size                   // top/left samples
@@ -178,23 +165,22 @@ static VP8Encoder* InitVP8Encoder(const WebPConfig* const config,
   printf("===================================\n");
   printf("Memory used:\n"
          "             encoder: %ld\n"
-         "         block cache: %ld\n"
          "                info: %ld\n"
          "               preds: %ld\n"
          "         top samples: %ld\n"
          "            non-zero: %ld\n"
          "            lf-stats: %ld\n"
          "               total: %ld\n",
-         sizeof(VP8Encoder) + ALIGN_CST, cache_size, info_size,
+         sizeof(VP8Encoder) + WEBP_ALIGN_CST, info_size,
          preds_size, samples_size, nz_size, lf_stats_size, size);
-  printf("Transcient object sizes:\n"
+  printf("Transient object sizes:\n"
          "      VP8EncIterator: %ld\n"
          "        VP8ModeScore: %ld\n"
          "      VP8SegmentInfo: %ld\n"
-         "            VP8Proba: %ld\n"
+         "         VP8EncProba: %ld\n"
          "             LFStats: %ld\n",
          sizeof(VP8EncIterator), sizeof(VP8ModeScore),
-         sizeof(VP8SegmentInfo), sizeof(VP8Proba),
+         sizeof(VP8SegmentInfo), sizeof(VP8EncProba),
          sizeof(LFStats));
   printf("Picture size (yuv): %ld\n",
          mb_w * mb_h * 384 * sizeof(uint8_t));
@@ -206,41 +192,27 @@ static VP8Encoder* InitVP8Encoder(const WebPConfig* const config,
     return NULL;
   }
   enc = (VP8Encoder*)mem;
-  mem = (uint8_t*)DO_ALIGN(mem + sizeof(*enc));
+  mem = (uint8_t*)WEBP_ALIGN(mem + sizeof(*enc));
   memset(enc, 0, sizeof(*enc));
   enc->num_parts_ = 1 << config->partitions;
   enc->mb_w_ = mb_w;
   enc->mb_h_ = mb_h;
   enc->preds_w_ = preds_w;
-  enc->yuv_in_ = (uint8_t*)mem;
-  mem += YUV_SIZE;
-  enc->yuv_out_ = (uint8_t*)mem;
-  mem += YUV_SIZE;
-  enc->yuv_out2_ = (uint8_t*)mem;
-  mem += YUV_SIZE;
-  enc->yuv_p_ = (uint8_t*)mem;
-  mem += PRED_SIZE;
   enc->mb_info_ = (VP8MBInfo*)mem;
   mem += info_size;
   enc->preds_ = ((uint8_t*)mem) + 1 + enc->preds_w_;
   mem += preds_w * preds_h * sizeof(uint8_t);
-  enc->nz_ = 1 + (uint32_t*)mem;
+  enc->nz_ = 1 + (uint32_t*)WEBP_ALIGN(mem);
   mem += nz_size;
-  enc->lf_stats_ = lf_stats_size ? (LFStats*)DO_ALIGN(mem) : NULL;
+  enc->lf_stats_ = lf_stats_size ? (LFStats*)WEBP_ALIGN(mem) : NULL;
   mem += lf_stats_size;
 
   // top samples (all 16-aligned)
-  mem = (uint8_t*)DO_ALIGN(mem);
+  mem = (uint8_t*)WEBP_ALIGN(mem);
   enc->y_top_ = (uint8_t*)mem;
   enc->uv_top_ = enc->y_top_ + top_stride;
   mem += 2 * top_stride;
-  mem = (uint8_t*)DO_ALIGN(mem + 1);
-  enc->y_left_ = (uint8_t*)mem;
-  mem += 16 + 16;
-  enc->u_left_ = (uint8_t*)mem;
-  mem += 16;
-  enc->v_left_ = (uint8_t*)mem;
-  mem += 8;
+  assert(mem <= (uint8_t*)enc + size);
 
   enc->config_ = config;
   enc->profile_ = use_filter ? ((config->filter_type == 1) ? 0 : 1) : 2;
@@ -253,29 +225,32 @@ static VP8Encoder* InitVP8Encoder(const WebPConfig* const config,
   ResetSegmentHeader(enc);
   ResetFilterHeader(enc);
   ResetBoundaryPredictions(enc);
-
+  VP8EncDspCostInit();
   VP8EncInitAlpha(enc);
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-  VP8EncInitLayer(enc);
-#endif
 
+  // lower quality means smaller output -> we modulate a little the page
+  // size based on quality. This is just a crude 1rst-order prediction.
+  {
+    const float scale = 1.f + config->quality * 5.f / 100.f;  // in [1,6]
+    VP8TBufferInit(&enc->tokens_, (int)(mb_w * mb_h * 4 * scale));
+  }
   return enc;
 }
 
-static void DeleteVP8Encoder(VP8Encoder* enc) {
+static int DeleteVP8Encoder(VP8Encoder* enc) {
+  int ok = 1;
   if (enc != NULL) {
-    VP8EncDeleteAlpha(enc);
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    VP8EncDeleteLayer(enc);
-#endif
-    free(enc);
+    ok = VP8EncDeleteAlpha(enc);
+    VP8TBufferClear(&enc->tokens_);
+    WebPSafeFree(enc);
   }
+  return ok;
 }
 
 //------------------------------------------------------------------------------
 
 static double GetPSNR(uint64_t err, uint64_t size) {
-  return err ? 10. * log10(255. * 255. * size / err) : 99.;
+  return (err > 0 && size > 0) ? 10. * log10(255. * 255. * size / err) : 99.;
 }
 
 static void FinalizePSNR(const VP8Encoder* const enc) {
@@ -332,7 +307,7 @@ int WebPReportProgress(const WebPPicture* const pic,
 //------------------------------------------------------------------------------
 
 int WebPEncode(const WebPConfig* config, WebPPicture* pic) {
-  int ok;
+  int ok = 0;
 
   if (pic == NULL)
     return 0;
@@ -346,44 +321,63 @@ int WebPEncode(const WebPConfig* config, WebPPicture* pic) {
   if (pic->width > WEBP_MAX_DIMENSION || pic->height > WEBP_MAX_DIMENSION)
     return WebPEncodingSetError(pic, VP8_ENC_ERROR_BAD_DIMENSION);
 
+  if (!config->exact) {
+    WebPCleanupTransparentArea(pic);
+  }
+
   if (pic->stats != NULL) memset(pic->stats, 0, sizeof(*pic->stats));
 
   if (!config->lossless) {
     VP8Encoder* enc = NULL;
-    if (pic->y == NULL || pic->u == NULL || pic->v == NULL) {
-      if (pic->argb != NULL) {
-        if (!WebPPictureARGBToYUVA(pic, WEBP_YUV420)) return 0;
+    if (pic->use_argb || pic->y == NULL || pic->u == NULL || pic->v == NULL) {
+      // Make sure we have YUVA samples.
+      if (config->preprocessing & 4) {
+        if (!WebPPictureSmartARGBToYUVA(pic)) {
+          return 0;
+        }
       } else {
-        return WebPEncodingSetError(pic, VP8_ENC_ERROR_NULL_PARAMETER);
+        float dithering = 0.f;
+        if (config->preprocessing & 2) {
+          const float x = config->quality / 100.f;
+          const float x2 = x * x;
+          // slowly decreasing from max dithering at low quality (q->0)
+          // to 0.5 dithering amplitude at high quality (q->100)
+          dithering = 1.0f + (0.5f - 1.0f) * x2 * x2;
+        }
+        if (!WebPPictureARGBToYUVADithered(pic, WEBP_YUV420, dithering)) {
+          return 0;
+        }
       }
     }
 
     enc = InitVP8Encoder(config, pic);
     if (enc == NULL) return 0;  // pic->error is already set.
     // Note: each of the tasks below account for 20% in the progress report.
-    ok = VP8EncAnalyze(enc)
-      && VP8StatLoop(enc)
-      && VP8EncLoop(enc)
-      && VP8EncFinishAlpha(enc)
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-      && VP8EncFinishLayer(enc)
-#endif
-      && VP8EncWrite(enc);
+    ok = VP8EncAnalyze(enc);
+
+    // Analysis is done, proceed to actual coding.
+    ok = ok && VP8EncStartAlpha(enc);   // possibly done in parallel
+    if (!enc->use_tokens_) {
+      ok = ok && VP8EncLoop(enc);
+    } else {
+      ok = ok && VP8EncTokenLoop(enc);
+    }
+    ok = ok && VP8EncFinishAlpha(enc);
+
+    ok = ok && VP8EncWrite(enc);
     StoreStats(enc);
     if (!ok) {
       VP8EncFreeBitWriters(enc);
     }
-    DeleteVP8Encoder(enc);
+    ok &= DeleteVP8Encoder(enc);  // must always be called, even if !ok
   } else {
-    if (pic->argb == NULL)
-      return WebPEncodingSetError(pic, VP8_ENC_ERROR_NULL_PARAMETER);
+    // Make sure we have ARGB samples.
+    if (pic->argb == NULL && !WebPPictureYUVAToARGB(pic)) {
+      return 0;
+    }
 
     ok = VP8LEncodeImage(config, pic);  // Sets pic->error in case of problem.
   }
 
   return ok;
 }
-
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif