diff options
Diffstat (limited to 'thirdparty/libwebp/src/enc/quant_enc.c')
| -rw-r--r-- | thirdparty/libwebp/src/enc/quant_enc.c | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/thirdparty/libwebp/src/enc/quant_enc.c b/thirdparty/libwebp/src/enc/quant_enc.c index 3b1a3129b5..35bfaf21ef 100644 --- a/thirdparty/libwebp/src/enc/quant_enc.c +++ b/thirdparty/libwebp/src/enc/quant_enc.c @@ -826,6 +826,85 @@ static int ReconstructIntra4(VP8EncIterator* const it, return nz; } +//------------------------------------------------------------------------------ +// DC-error diffusion + +// Diffusion weights. We under-correct a bit (15/16th of the error is actually +// diffused) to avoid 'rainbow' chessboard pattern of blocks at q~=0. +#define C1 7 // fraction of error sent to the 4x4 block below +#define C2 8 // fraction of error sent to the 4x4 block on the right +#define DSHIFT 4 +#define DSCALE 1 // storage descaling, needed to make the error fit int8_t + +// Quantize as usual, but also compute and return the quantization error. +// Error is already divided by DSHIFT. +static int QuantizeSingle(int16_t* const v, const VP8Matrix* const mtx) { + int V = *v; + const int sign = (V < 0); + if (sign) V = -V; + if (V > (int)mtx->zthresh_[0]) { + const int qV = QUANTDIV(V, mtx->iq_[0], mtx->bias_[0]) * mtx->q_[0]; + const int err = (V - qV); + *v = sign ? -qV : qV; + return (sign ? -err : err) >> DSCALE; + } + *v = 0; + return (sign ? -V : V) >> DSCALE; +} + +static void CorrectDCValues(const VP8EncIterator* const it, + const VP8Matrix* const mtx, + int16_t tmp[][16], VP8ModeScore* const rd) { + // | top[0] | top[1] + // --------+--------+--------- + // left[0] | tmp[0] tmp[1] <-> err0 err1 + // left[1] | tmp[2] tmp[3] err2 err3 + // + // Final errors {err1,err2,err3} are preserved and later restored + // as top[]/left[] on the next block. + int ch; + for (ch = 0; ch <= 1; ++ch) { + const int8_t* const top = it->top_derr_[it->x_][ch]; + const int8_t* const left = it->left_derr_[ch]; + int16_t (* const c)[16] = &tmp[ch * 4]; + int err0, err1, err2, err3; + c[0][0] += (C1 * top[0] + C2 * left[0]) >> (DSHIFT - DSCALE); + err0 = QuantizeSingle(&c[0][0], mtx); + c[1][0] += (C1 * top[1] + C2 * err0) >> (DSHIFT - DSCALE); + err1 = QuantizeSingle(&c[1][0], mtx); + c[2][0] += (C1 * err0 + C2 * left[1]) >> (DSHIFT - DSCALE); + err2 = QuantizeSingle(&c[2][0], mtx); + c[3][0] += (C1 * err1 + C2 * err2) >> (DSHIFT - DSCALE); + err3 = QuantizeSingle(&c[3][0], mtx); + // error 'err' is bounded by mtx->q_[0] which is 132 at max. Hence + // err >> DSCALE will fit in an int8_t type if DSCALE>=1. + assert(abs(err1) <= 127 && abs(err2) <= 127 && abs(err3) <= 127); + rd->derr[ch][0] = (int8_t)err1; + rd->derr[ch][1] = (int8_t)err2; + rd->derr[ch][2] = (int8_t)err3; + } +} + +static void StoreDiffusionErrors(VP8EncIterator* const it, + const VP8ModeScore* const rd) { + int ch; + for (ch = 0; ch <= 1; ++ch) { + int8_t* const top = it->top_derr_[it->x_][ch]; + int8_t* const left = it->left_derr_[ch]; + left[0] = rd->derr[ch][0]; // restore err1 + left[1] = 3 * rd->derr[ch][2] >> 2; // ... 3/4th of err3 + top[0] = rd->derr[ch][1]; // ... err2 + top[1] = rd->derr[ch][2] - left[1]; // ... 1/4th of err3. + } +} + +#undef C1 +#undef C2 +#undef DSHIFT +#undef DSCALE + +//------------------------------------------------------------------------------ + static int ReconstructUV(VP8EncIterator* const it, VP8ModeScore* const rd, uint8_t* const yuv_out, int mode) { const VP8Encoder* const enc = it->enc_; @@ -839,6 +918,8 @@ static int ReconstructUV(VP8EncIterator* const it, VP8ModeScore* const rd, for (n = 0; n < 8; n += 2) { VP8FTransform2(src + VP8ScanUV[n], ref + VP8ScanUV[n], tmp[n]); } + if (it->top_derr_ != NULL) CorrectDCValues(it, &dqm->uv_, tmp, rd); + if (DO_TRELLIS_UV && it->do_trellis_) { int ch, x, y; for (ch = 0, n = 0; ch <= 2; ch += 2) { @@ -1101,6 +1182,9 @@ static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) { CopyScore(&rd_best, &rd_uv); rd->mode_uv = mode; memcpy(rd->uv_levels, rd_uv.uv_levels, sizeof(rd->uv_levels)); + if (it->top_derr_ != NULL) { + memcpy(rd->derr, rd_uv.derr, sizeof(rd_uv.derr)); + } SwapPtr(&dst, &tmp_dst); } } @@ -1109,6 +1193,9 @@ static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) { if (dst != dst0) { // copy 16x8 block if needed VP8Copy16x8(dst, dst0); } + if (it->top_derr_ != NULL) { // store diffusion errors for next block + StoreDiffusionErrors(it, rd); + } } //------------------------------------------------------------------------------ |