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Speedup AnalyzeAndInit for low effort compression.

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AnalyzeSubtractGreen constitutes about 8-10% of the comression CPU cycles.
Statistically, subtract-green is proved to be useful for most of the
non-palette compression. So instead of evaluating the entropy (by calling
AnalyzeSubtractGreen) apply subtract-green transform for the low-effort
compression.

This changes speeds up the compression at m=0 by 8-10% (with very slight loss
of 0.07% in the compression density).

Change-Id: I9797dc39437ae089716acb14631bbc77d367acf4
This commit is contained in:
Vikas Arora 2015-01-30 10:31:14 -08:00
parent a6597483af
commit 72831f6b28
1 changed files with 15 additions and 6 deletions
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15
src/enc/vp8l.c
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@ -305,7 +305,9 @@ static int AnalyzeAndInit(VP8LEncoder* const enc, WebPImageHint image_hint) {
const int method = config->method; const int method = config->method;
const int low_effort = (config->method == 0); const int low_effort = (config->method == 0);
const float quality = config->quality; const float quality = config->quality;
double subtract_green_score = 10.f; double subtract_green_score = 10.0;
const double subtract_green_threshold_palette = 0.80;
const double subtract_green_threshold_non_palette = 1.0;
// we round the block size up, so we're guaranteed to have // we round the block size up, so we're guaranteed to have
// at max MAX_REFS_BLOCK_PER_IMAGE blocks used: // at max MAX_REFS_BLOCK_PER_IMAGE blocks used:
int refs_block_size = (pix_cnt - 1) / MAX_REFS_BLOCK_PER_IMAGE + 1; int refs_block_size = (pix_cnt - 1) / MAX_REFS_BLOCK_PER_IMAGE + 1;
@ -316,11 +318,18 @@ static int AnalyzeAndInit(VP8LEncoder* const enc, WebPImageHint image_hint) {
if (!enc->use_palette_ || if (!enc->use_palette_ ||
EvalSubtractGreenForPalette(enc->palette_size_, quality)) { EvalSubtractGreenForPalette(enc->palette_size_, quality)) {
if (low_effort) {
// For low effort compression, avoid calling (costly) method
// AnalyzeSubtractGreen and enable the subtract-green transform
// for non-palette images.
subtract_green_score = subtract_green_threshold_non_palette * 0.99;
} else {
if (!AnalyzeSubtractGreen(pic->argb, width, height, if (!AnalyzeSubtractGreen(pic->argb, width, height,
&subtract_green_score)) { &subtract_green_score)) {
return 0; return 0;
} }
} }
}
// Evaluate histogram bits based on the original value of use_palette flag. // Evaluate histogram bits based on the original value of use_palette flag.
enc->histo_bits_ = GetHistoBits(method, enc->use_palette_, pic->width, enc->histo_bits_ = GetHistoBits(method, enc->use_palette_, pic->width,
@ -330,13 +339,13 @@ static int AnalyzeAndInit(VP8LEncoder* const enc, WebPImageHint image_hint) {
enc->use_subtract_green_ = 0; enc->use_subtract_green_ = 0;
if (enc->use_palette_) { if (enc->use_palette_) {
// Check if other transforms (subtract green etc) are potentially better. // Check if other transforms (subtract green etc) are potentially better.
if (subtract_green_score < 0.80f) { if (subtract_green_score < subtract_green_threshold_palette) {
enc->use_subtract_green_ = 1; enc->use_subtract_green_ = 1;
enc->use_palette_ = 0; enc->use_palette_ = 0;
} }
} else { } else {
// Non-palette case, check if subtract-green optimizes the entropy. // Non-palette case, check if subtract-green optimizes the entropy.
if (subtract_green_score < 1.0f) { if (subtract_green_score < subtract_green_threshold_non_palette) {
enc->use_subtract_green_ = 1; enc->use_subtract_green_ = 1;
} }
} }