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Diffstat (limited to 'drivers/webp/enc/near_lossless.c')
| -rw-r--r-- | drivers/webp/enc/near_lossless.c | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/drivers/webp/enc/near_lossless.c b/drivers/webp/enc/near_lossless.c new file mode 100644 index 0000000000..9bc0f0e786 --- /dev/null +++ b/drivers/webp/enc/near_lossless.c @@ -0,0 +1,160 @@ +// Copyright 2014 Google Inc. All Rights Reserved. +// +// 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. +// ----------------------------------------------------------------------------- +// +// Near-lossless image preprocessing adjusts pixel values to help +// compressibility with a guarantee of maximum deviation between original and +// resulting pixel values. +// +// Author: Jyrki Alakuijala (jyrki@google.com) +// Converted to C by Aleksander Kramarz (akramarz@google.com) + +#include <stdlib.h> + +#include "../dsp/lossless.h" +#include "../utils/utils.h" +#include "./vp8enci.h" + +#define MIN_DIM_FOR_NEAR_LOSSLESS 64 +#define MAX_LIMIT_BITS 5 + +// Computes quantized pixel value and distance from original value. +static void GetValAndDistance(int a, int initial, int bits, + int* const val, int* const distance) { + const int mask = ~((1 << bits) - 1); + *val = (initial & mask) | (initial >> (8 - bits)); + *distance = 2 * abs(a - *val); +} + +// Clamps the value to range [0, 255]. +static int Clamp8b(int val) { + const int min_val = 0; + const int max_val = 0xff; + return (val < min_val) ? min_val : (val > max_val) ? max_val : val; +} + +// Quantizes values {a, a+(1<<bits), a-(1<<bits)} and returns the nearest one. +static int FindClosestDiscretized(int a, int bits) { + int best_val = a, i; + int min_distance = 256; + + for (i = -1; i <= 1; ++i) { + int candidate, distance; + const int val = Clamp8b(a + i * (1 << bits)); + GetValAndDistance(a, val, bits, &candidate, &distance); + if (i != 0) { + ++distance; + } + // Smallest distance but favor i == 0 over i == -1 and i == 1 + // since that keeps the overall intensity more constant in the + // images. + if (distance < min_distance) { + min_distance = distance; + best_val = candidate; + } + } + return best_val; +} + +// Applies FindClosestDiscretized to all channels of pixel. +static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) { + return + (FindClosestDiscretized(a >> 24, bits) << 24) | + (FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) | + (FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) | + (FindClosestDiscretized(a & 0xff, bits)); +} + +// Checks if distance between corresponding channel values of pixels a and b +// is within the given limit. +static int IsNear(uint32_t a, uint32_t b, int limit) { + int k; + for (k = 0; k < 4; ++k) { + const int delta = + (int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff); + if (delta >= limit || delta <= -limit) { + return 0; + } + } + return 1; +} + +static int IsSmooth(const uint32_t* const prev_row, + const uint32_t* const curr_row, + const uint32_t* const next_row, + int ix, int limit) { + // Check that all pixels in 4-connected neighborhood are smooth. + return (IsNear(curr_row[ix], curr_row[ix - 1], limit) && + IsNear(curr_row[ix], curr_row[ix + 1], limit) && + IsNear(curr_row[ix], prev_row[ix], limit) && + IsNear(curr_row[ix], next_row[ix], limit)); +} + +// Adjusts pixel values of image with given maximum error. +static void NearLossless(int xsize, int ysize, uint32_t* argb, + int limit_bits, uint32_t* copy_buffer) { + int x, y; + const int limit = 1 << limit_bits; + uint32_t* prev_row = copy_buffer; + uint32_t* curr_row = prev_row + xsize; + uint32_t* next_row = curr_row + xsize; + memcpy(copy_buffer, argb, xsize * 2 * sizeof(argb[0])); + + for (y = 1; y < ysize - 1; ++y) { + uint32_t* const curr_argb_row = argb + y * xsize; + uint32_t* const next_argb_row = curr_argb_row + xsize; + memcpy(next_row, next_argb_row, xsize * sizeof(argb[0])); + for (x = 1; x < xsize - 1; ++x) { + if (!IsSmooth(prev_row, curr_row, next_row, x, limit)) { + curr_argb_row[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits); + } + } + { + // Three-way swap. + uint32_t* const temp = prev_row; + prev_row = curr_row; + curr_row = next_row; + next_row = temp; + } + } +} + +static int QualityToLimitBits(int quality) { + // quality mapping: + // 0..19 -> 5 + // 0..39 -> 4 + // 0..59 -> 3 + // 0..79 -> 2 + // 0..99 -> 1 + // 100 -> 0 + return MAX_LIMIT_BITS - quality / 20; +} + +int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) { + int i; + uint32_t* const copy_buffer = + (uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer)); + const int limit_bits = QualityToLimitBits(quality); + assert(argb != NULL); + assert(limit_bits >= 0); + assert(limit_bits <= MAX_LIMIT_BITS); + if (copy_buffer == NULL) { + return 0; + } + // For small icon images, don't attempt to apply near-lossless compression. + if (xsize < MIN_DIM_FOR_NEAR_LOSSLESS && ysize < MIN_DIM_FOR_NEAR_LOSSLESS) { + WebPSafeFree(copy_buffer); + return 1; + } + + for (i = limit_bits; i != 0; --i) { + NearLossless(xsize, ysize, argb, i, copy_buffer); + } + WebPSafeFree(copy_buffer); + return 1; +} |