dany/libwebp
1
0
Fork 0
mirror of https://github.com/webmproject/libwebp.git synced 2024-12-27 22:28:22 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity

Merge "lossless: 0.13% compression density gain"

Browse Source
This commit is contained in:
James Zern 2015-06-03 03:02:08 +00:00 committed by Gerrit Code Review
commit 65ef5afc27
1 changed files with 37 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

68
src/dsp/lossless_enc.c
View File

@ -927,49 +927,55 @@ static float GetPredictionCostCrossColorBlue(
return cur_diff;
}
#define kGreenRedToBlueNumAxis 8
#define kGreenRedToBlueMaxIters 7
static void GetBestGreenRedToBlue(
const uint32_t* argb, int stride, int tile_width, int tile_height,
VP8LMultipliers prev_x, VP8LMultipliers prev_y, int quality,
const int accumulated_blue_histo[256],
VP8LMultipliers* const best_tx) {
float best_diff = MAX_DIFF_COST;
float cur_diff;
const int step = (quality < 25) ? 32 : (quality > 50) ? 8 : 16;
const int min_green_to_blue = -32;
const int max_green_to_blue = 32;
const int min_red_to_blue = -32;
const int max_red_to_blue = 32;
const int num_iters =
(1 + (max_green_to_blue - min_green_to_blue) / step) *
(1 + (max_red_to_blue - min_red_to_blue) / step);
// Number of tries to get optimal green_to_blue & red_to_blue color transforms
// after finding a local minima.
const int max_tries_after_min = 4 + (num_iters >> 2);
int num_tries_after_min = 0;
int green_to_blue;
for (green_to_blue = min_green_to_blue;
green_to_blue <= max_green_to_blue &&
num_tries_after_min < max_tries_after_min;
green_to_blue += step) {
int red_to_blue;
for (red_to_blue = min_red_to_blue;
red_to_blue <= max_red_to_blue &&
num_tries_after_min < max_tries_after_min;
red_to_blue += step) {
cur_diff = GetPredictionCostCrossColorBlue(
const int8_t offset[kGreenRedToBlueNumAxis][2] =
{{0, -1}, {0, 1}, {-1, 0}, {1, 0}, {-1, -1}, {-1, 1}, {1, -1}, {1, 1}};
const int8_t delta_lut[kGreenRedToBlueMaxIters] = { 16, 16, 8, 4, 2, 2, 2 };
const int iters =
(quality < 25) ? 1 : (quality > 50) ? kGreenRedToBlueMaxIters : 4;
int green_to_blue_best = 0;
int red_to_blue_best = 0;
int iter;
// Initial value at origin:
float best_diff = GetPredictionCostCrossColorBlue(
argb, stride, tile_width, tile_height, prev_x, prev_y,
green_to_blue, red_to_blue, accumulated_blue_histo);
green_to_blue_best, red_to_blue_best, accumulated_blue_histo);
for (iter = 0; iter < iters; ++iter) {
const int delta = delta_lut[iter];
int axis;
for (axis = 0; axis < kGreenRedToBlueNumAxis; ++axis) {
const int green_to_blue_cur =
offset[axis][0] * delta + green_to_blue_best;
const int red_to_blue_cur = offset[axis][1] * delta + red_to_blue_best;
const float cur_diff = GetPredictionCostCrossColorBlue(
argb, stride, tile_width, tile_height, prev_x, prev_y,
green_to_blue_cur, red_to_blue_cur, accumulated_blue_histo);
if (cur_diff < best_diff) {
best_diff = cur_diff;
best_tx->green_to_blue_ = green_to_blue;
best_tx->red_to_blue_ = red_to_blue;
num_tries_after_min = 0;
} else {
++num_tries_after_min;
green_to_blue_best = green_to_blue_cur;
red_to_blue_best = red_to_blue_cur;
}
if (quality < 25 && iter == 4) {
// Only axis aligned diffs for lower quality.
break; // next iter.
}
}
if (delta == 2 && green_to_blue_best == 0 && red_to_blue_best == 0) {
// Further iterations would not help.
break; // out of iter-loop.
}
}
best_tx->green_to_blue_ = green_to_blue_best;
best_tx->red_to_blue_ = red_to_blue_best;
}
#undef kGreenRedToBlueMaxIters
#undef kGreenRedToBlueNumAxis
static VP8LMultipliers GetBestColorTransformForTile(
int tile_x, int tile_y, int bits,