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Update encoding heuristic w.r.t palette colors.

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Added a threshold of MAX_COLORS_FOR_GRAPH for color-palettes, above
which the graph hint is ignored.

Change-Id: Ia5d7f45e52731b6eaf2806999d6be82861744fd3
This commit is contained in:
Vikas Arora 2012-08-08 14:28:25 -07:00
parent 6f4272b090
commit 62dd9bb242
1 changed files with 32 additions and 19 deletions
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51
src/enc/vp8l.c
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@ -29,6 +29,7 @@ extern "C" {
#define PALETTE_KEY_RIGHT_SHIFT 22 // Key for 1K buffer.
#define MAX_HUFF_IMAGE_SIZE (16 * 1024 * 1024)
#define MAX_COLORS_FOR_GRAPH 64
// -----------------------------------------------------------------------------
// Palette
@ -98,11 +99,11 @@ static int AnalyzeAndCreatePalette(const WebPPicture* const pic,
return 1;
}
static int AnalyzeEntropy(const WebPPicture* const pic,
static int AnalyzeEntropy(const uint32_t* argb,
int width, int height, int argb_stride,
double* const nonpredicted_bits,
double* const predicted_bits) {
int x, y;
const uint32_t* argb = pic->argb;
const uint32_t* last_line = NULL;
uint32_t last_pix = argb[0]; // so we're sure that pix_diff == 0
@ -114,8 +115,8 @@ static int AnalyzeEntropy(const WebPPicture* const pic,
VP8LHistogramInit(predicted, 0);
VP8LHistogramInit(nonpredicted, 0);
for (y = 0; y < pic->height; ++y) {
for (x = 0; x < pic->width; ++x) {
for (y = 0; y < height; ++y) {
for (x = 0; x < width; ++x) {
const uint32_t pix = argb[x];
const uint32_t pix_diff = VP8LSubPixels(pix, last_pix);
if (pix_diff == 0) continue;
@ -131,7 +132,7 @@ static int AnalyzeEntropy(const WebPPicture* const pic,
}
}
last_line = argb;
argb += pic->argb_stride;
argb += argb_stride;
}
*nonpredicted_bits = VP8LHistogramEstimateBitsBulk(nonpredicted);
*predicted_bits = VP8LHistogramEstimateBitsBulk(predicted);
@ -143,24 +144,35 @@ static int VP8LEncAnalyze(VP8LEncoder* const enc, WebPImageHint image_hint) {
const WebPPicture* const pic = enc->pic_;
assert(pic != NULL && pic->argb != NULL);
enc->use_palette_ = (image_hint == WEBP_HINT_GRAPH) ? 0 :
enc->use_palette_ =
AnalyzeAndCreatePalette(pic, enc->palette_, &enc->palette_size_);
if (!enc->use_palette_) {
if (image_hint == WEBP_HINT_DEFAULT) {
double non_pred_entropy, pred_entropy;
if (!AnalyzeEntropy(pic, &non_pred_entropy, &pred_entropy)) {
return 0;
}
if (pred_entropy < 0.95 * non_pred_entropy) {
enc->use_predict_ = 1;
enc->use_cross_color_ = 1;
}
} else if (image_hint == WEBP_HINT_PHOTO) {
enc->use_predict_ = 1;
enc->use_cross_color_ = 1;
if (image_hint == WEBP_HINT_GRAPH) {
if (enc->use_palette_ && enc->palette_size_ < MAX_COLORS_FOR_GRAPH) {
enc->use_palette_ = 0;
}
}
if (!enc->use_palette_) {
if (image_hint == WEBP_HINT_PHOTO) {
enc->use_predict_ = 1;
enc->use_cross_color_ = 1;
} else {
double non_pred_entropy, pred_entropy;
if (!AnalyzeEntropy(pic->argb, pic->width, pic->height, pic->argb_stride,
&non_pred_entropy, &pred_entropy)) {
return 0;
}
if (pred_entropy < 0.95 * non_pred_entropy) {
enc->use_predict_ = 1;
// TODO(vikasa): Observed some correlation of cross_color transform with
// predict. Need to investigate this further and add separate heuristic
// for setting use_cross_color flag.
enc->use_cross_color_ = 1;
}
}
}
return 1;
}
@ -961,6 +973,7 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
if (enc->use_palette_) {
err = ApplyPalette(bw, enc, quality);
if (err != VP8_ENC_OK) goto Error;
// Color cache is disabled for palette.
enc->cache_bits_ = 0;
}