dany/libwebp
1
0
Fork 0
mirror of https://github.com/webmproject/libwebp.git synced 2025-10-30 18:05:36 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity

lossless: 0.06 % compression density improvement

Browse Source 
Change-Id: Ib662e6aec53b40d6bc736d3ecfd6475bb005c790
This commit is contained in:
Pascal Massimino
2015-06-02 14:51:51 +02:00
parent 64960da9e1
commit 3033f24c26
1 changed files with 24 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

56
src/dsp/lossless_enc.c
View File

@@ -854,40 +854,32 @@ static float GetPredictionCostCrossColorRed(
static void GetBestGreenToRed( static void GetBestGreenToRed(
const uint32_t* argb, int stride, int tile_width, int tile_height, const uint32_t* argb, int stride, int tile_width, int tile_height,
VP8LMultipliers prev_x, VP8LMultipliers prev_y, VP8LMultipliers prev_x, VP8LMultipliers prev_y, int quality,
const int accumulated_red_histo[256], VP8LMultipliers* const best_tx) { const int accumulated_red_histo[256], VP8LMultipliers* const best_tx) {
int min_green_to_red = -64; const int kMaxIters = 4 + ((7 * quality) >> 8); // in range [4..6]
int max_green_to_red = 64; int green_to_red_best = 0;
int green_to_red = 0; int iter, offset;
int eval_min = 1; float best_diff = GetPredictionCostCrossColorRed(
int eval_max = 1; argb, stride, tile_width, tile_height, prev_x, prev_y,
float cur_diff_min = MAX_DIFF_COST; green_to_red_best, accumulated_red_histo);
float cur_diff_max = MAX_DIFF_COST; for (iter = 0; iter < kMaxIters; ++iter) {
// Do a binary search to find the optimal green_to_red color transform. // ColorTransformDelta is a 3.5 bit fixed point, so 32 is equal to
while (max_green_to_red - min_green_to_red > 2) { // one in color computation. Having initial delta here as 1 is sufficient
if (eval_min) { // to explore the range of (-2, 2).
cur_diff_min = GetPredictionCostCrossColorRed( const int delta = 32 >> iter;
argb, stride, tile_width, tile_height, // Try a negative and a positive delta from the best known value.
prev_x, prev_y, min_green_to_red, accumulated_red_histo); for (offset = -delta; offset <= delta; offset += 2 * delta) {
eval_min = 0; const int green_to_red_cur = offset + green_to_red_best;
} const float cur_diff = GetPredictionCostCrossColorRed(
if (eval_max) { argb, stride, tile_width, tile_height, prev_x, prev_y,
cur_diff_max = GetPredictionCostCrossColorRed( green_to_red_cur, accumulated_red_histo);
argb, stride, tile_width, tile_height, if (cur_diff < best_diff) {
prev_x, prev_y, max_green_to_red, accumulated_red_histo); best_diff = cur_diff;
eval_max = 0; green_to_red_best = green_to_red_cur;
}
if (cur_diff_min < cur_diff_max) {
green_to_red = min_green_to_red;
max_green_to_red = (max_green_to_red + min_green_to_red) / 2;
eval_max = 1;
} else {
green_to_red = max_green_to_red;
min_green_to_red = (max_green_to_red + min_green_to_red) / 2;
eval_min = 1;
} }
} }
best_tx->green_to_red_ = green_to_red; }
best_tx->green_to_red_ = green_to_red_best;
} }
static void CollectColorBlueTransforms(const uint32_t* argb, int stride, static void CollectColorBlueTransforms(const uint32_t* argb, int stride,
@@ -1000,7 +992,7 @@ static VP8LMultipliers GetBestColorTransformForTile(
MultipliersClear(&best_tx); MultipliersClear(&best_tx);
GetBestGreenToRed(tile_argb, xsize, tile_width, tile_height, GetBestGreenToRed(tile_argb, xsize, tile_width, tile_height,
prev_x, prev_y, accumulated_red_histo, &best_tx); prev_x, prev_y, quality, accumulated_red_histo, &best_tx);
GetBestGreenRedToBlue(tile_argb, xsize, tile_width, tile_height, GetBestGreenRedToBlue(tile_argb, xsize, tile_width, tile_height,
prev_x, prev_y, quality, accumulated_blue_histo, prev_x, prev_y, quality, accumulated_blue_histo,
&best_tx); &best_tx);