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lossless: Add zeroes into the predicted histograms.

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Increases compression density by 0.03 % for lossy.

Speeds up at least one of the lossy alpha images by 20 %.

Palette entropy 'kludge' seems to save 1-2 % on alpha images.

Change-Id: I2116b8d81593ac8173bfba54a7c833997fca0804
This commit is contained in:
Jyrki Alakuijala
2015-06-19 10:17:46 +00:00
committed by James Zern
parent 85b44d8a69
commit 7b23b19808
1 changed files with 14 additions and 3 deletions
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17
src/enc/vp8l.c
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@@ -217,7 +217,7 @@ typedef enum {
} HistoIx;
static void AddSingleSubGreen(uint32_t p, uint32_t* r, uint32_t* b) {
const uint32_t green = (p >> 8) & 0xff;
const uint32_t green = p >> 8; // The upper bits are masked away later.
++r[((p >> 16) - green) & 0xff];
++b[(p - green) & 0xff];
}
@@ -281,6 +281,16 @@ static int AnalyzeEntropy(const uint32_t* argb,
EntropyIx last_mode_to_analyze =
use_palette ? kPalette : kSpatialSubGreen;
int j;
// Let's add one zero to the predicted histograms. The zeros are removed
// too efficiently by the pix_diff == 0 comparison, at least one of the
// zeros is likely to exist.
++histo[kHistoRedPredSubGreen * 256];
++histo[kHistoBluePredSubGreen * 256];
++histo[kHistoRedPred * 256];
++histo[kHistoGreenPred * 256];
++histo[kHistoBluePred * 256];
++histo[kHistoAlphaPred * 256];
for (j = 0; j < kHistoTotal; ++j) {
entropy_comp[j] = VP8LBitsEntropy(&histo[j * 256], 256, NULL);
}
@@ -300,11 +310,12 @@ static int AnalyzeEntropy(const uint32_t* argb,
entropy_comp[kHistoRedPredSubGreen] +
entropy_comp[kHistoGreenPred] +
entropy_comp[kHistoBluePredSubGreen];
entropy[kPalette] = entropy_comp[kHistoPalette];
// Palette mode seems more efficient in a breakeven case. Bias with 1.0.
entropy[kPalette] = entropy_comp[kHistoPalette] - 1.0;
*min_entropy_ix = kDirect;
for (k = kDirect + 1; k <= last_mode_to_analyze; ++k) {
if (entropy[*min_entropy_ix] >= entropy[k]) {
if (entropy[*min_entropy_ix] > entropy[k]) {
*min_entropy_ix = k;
}
}