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WebP-Lossless encoding improvements.

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Lossy (with Alpha) image compression gets 2.3X speedup.
Compressing lossless images is 20%-40% faster now.

Change-Id: I41f0225838b48ae5c60b1effd1b0de72fecb3ae6
(cherry picked from commit 8eae188a62)
This commit is contained in:
Vikas Arora
2013-05-08 17:19:04 -07:00
committed by James Zern
parent 26e7244221
commit 498d4dd634
6 changed files with 159 additions and 94 deletions
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65
src/enc/alpha.c
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@ -80,7 +80,7 @@ static int EncodeLossless(const uint8_t* const data, int width, int height,
config.lossless = 1;
config.method = effort_level; // impact is very small
// Set a moderate default quality setting for alpha.
config.quality = 5.f * effort_level;
config.quality = 10.f * effort_level;
assert(config.quality >= 0 && config.quality <= 100.f);
ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);
@ -156,6 +156,25 @@ static void CopyPlane(const uint8_t* src, int src_stride,
}
}
static int GetNumColors(const uint8_t* data, int width, int height,
int stride) {
int j;
int colors = 0;
uint8_t color[256] = { 0 };
for (j = 0; j < height; ++j) {
int i;
const uint8_t* const p = data + j * stride;
for (i = 0; i < width; ++i) {
color[p[i]] = 1;
}
}
for (j = 0; j < 256; ++j) {
if (color[j] > 0) ++colors;
}
return colors;
}
static int EncodeAlpha(VP8Encoder* const enc,
int quality, int method, int filter,
int effort_level,
@ -207,18 +226,32 @@ static int EncodeAlpha(VP8Encoder* const enc,
VP8BitWriter bw;
int test_filter;
uint8_t* filtered_alpha = NULL;
int try_filter_none = (effort_level > 3);
// We always test WEBP_FILTER_NONE first.
ok = EncodeAlphaInternal(quant_alpha, width, height,
method, WEBP_FILTER_NONE, reduce_levels,
effort_level, NULL, &bw, pic->stats);
if (!ok) {
VP8BitWriterWipeOut(&bw);
goto End;
if (filter == WEBP_FILTER_FAST) { // Quick estimate of the best candidate.
const int kMinColorsForFilterNone = 16;
const int kMaxColorsForFilterNone = 192;
const int num_colors = GetNumColors(quant_alpha, width, height, width);
// For low number of colors, NONE yeilds better compression.
filter = (num_colors <= kMinColorsForFilterNone) ? WEBP_FILTER_NONE :
EstimateBestFilter(quant_alpha, width, height, width);
// For large number of colors, try FILTER_NONE in addition to the best
// filter as well.
if (num_colors > kMaxColorsForFilterNone) {
try_filter_none = 1;
}
}
if (filter == WEBP_FILTER_FAST) { // Quick estimate of a second candidate?
filter = EstimateBestFilter(quant_alpha, width, height, width);
// Test for WEBP_FILTER_NONE for higher effort levels.
if (try_filter_none || filter == WEBP_FILTER_NONE) {
ok = EncodeAlphaInternal(quant_alpha, width, height,
method, WEBP_FILTER_NONE, reduce_levels,
effort_level, NULL, &bw, pic->stats);
if (!ok) {
VP8BitWriterWipeOut(&bw);
goto End;
}
}
// Stop?
if (filter == WEBP_FILTER_NONE) {
@ -234,11 +267,14 @@ static int EncodeAlpha(VP8Encoder* const enc,
// Try the other mode(s).
{
WebPAuxStats best_stats;
size_t best_score = VP8BitWriterSize(&bw);
size_t best_score = try_filter_none ?
VP8BitWriterSize(&bw) : (size_t)~0U;
int wipe_tmp_bw = try_filter_none;
memset(&best_stats, 0, sizeof(best_stats)); // prevent spurious warning
if (pic->stats != NULL) best_stats = *pic->stats;
for (test_filter = WEBP_FILTER_HORIZONTAL;
for (test_filter =
try_filter_none ? WEBP_FILTER_HORIZONTAL : WEBP_FILTER_NONE;
ok && (test_filter <= WEBP_FILTER_GRADIENT);
++test_filter) {
VP8BitWriter tmp_bw;
@ -262,7 +298,10 @@ static int EncodeAlpha(VP8Encoder* const enc,
} else {
VP8BitWriterWipeOut(&bw);
}
VP8BitWriterWipeOut(&tmp_bw);
if (wipe_tmp_bw) {
VP8BitWriterWipeOut(&tmp_bw);
}
wipe_tmp_bw = 1; // For next filter trial for WEBP_FILTER_BEST.
}
if (pic->stats != NULL) *pic->stats = best_stats;
}