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Provide one entry point for backward references.

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The new method VP8LGetBackwardReferences hides internal
heuristics used for choosing RLE or LZ77 based refs.
- Tuned VP8LHashChainFindCopy for better compression at higher Q.
- Refactored code.
- Removed the unused method VP8LVerifyBackwardReferences.

Change-Id: Ibb7bb072bab5a49a001577a20d88226f52e6c663
This commit is contained in:
Vikas Arora
2012-05-09 12:11:55 +05:30
parent c4ccab6463
commit e7167a2b95
3 changed files with 158 additions and 235 deletions
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85
src/enc/vp8l.c
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@ -157,86 +157,6 @@ static int VP8LEncAnalyze(VP8LEncoder* const enc) {
// -----------------------------------------------------------------------------
static int GetBackwardReferences(int width, int height,
const uint32_t* const argb,
int quality, int use_color_cache,
int cache_bits, int use_2d_locality,
VP8LBackwardRefs* const best) {
int ok = 0;
int lz77_is_useful;
VP8LBackwardRefs refs_rle, refs_lz77;
const int num_pix = width * height;
VP8LBackwardRefsAlloc(&refs_rle, num_pix);
VP8LBackwardRefsAlloc(&refs_lz77, num_pix);
VP8LInitBackwardRefs(best);
if (refs_rle.refs == NULL || refs_lz77.refs == NULL) {
Error1:
VP8LClearBackwardRefs(&refs_rle);
VP8LClearBackwardRefs(&refs_lz77);
goto End;
}
if (!VP8LBackwardReferencesHashChain(width, height, use_color_cache,
argb, cache_bits, quality,
&refs_lz77)) {
goto End;
}
// Backward Reference using RLE only.
VP8LBackwardReferencesRle(width, height, argb, &refs_rle);
{
double bit_cost_lz77, bit_cost_rle;
VP8LHistogram* const histo = (VP8LHistogram*)malloc(sizeof(*histo));
if (histo == NULL) goto Error1;
// Evaluate lz77 coding
VP8LHistogramCreate(histo, &refs_lz77, cache_bits);
bit_cost_lz77 = VP8LHistogramEstimateBits(histo);
// Evaluate RLE coding
VP8LHistogramCreate(histo, &refs_rle, cache_bits);
bit_cost_rle = VP8LHistogramEstimateBits(histo);
// Decide if LZ77 is useful.
lz77_is_useful = (bit_cost_lz77 < bit_cost_rle);
free(histo);
}
// Choose appropriate backward reference.
if (lz77_is_useful) {
// TraceBackwards is costly. Run it for higher qualities.
const int try_lz77_trace_backwards = (quality >= 75);
*best = refs_lz77; // default guess: lz77 is better
VP8LClearBackwardRefs(&refs_rle);
if (try_lz77_trace_backwards) {
const int recursion_level = (num_pix < 320 * 200) ? 1 : 0;
VP8LBackwardRefs refs_trace;
if (!VP8LBackwardRefsAlloc(&refs_trace, num_pix)) {
goto End;
}
if (VP8LBackwardReferencesTraceBackwards(width, height, recursion_level,
use_color_cache,
argb, cache_bits,
&refs_trace)) {
VP8LClearBackwardRefs(&refs_lz77);
*best = refs_trace;
}
}
} else {
VP8LClearBackwardRefs(&refs_lz77);
*best = refs_rle;
}
if (use_2d_locality) { // Use backward reference with 2D locality.
VP8LBackwardReferences2DLocality(width, best);
}
ok = 1;
End:
if (!ok) {
VP8LClearBackwardRefs(best);
}
return ok;
}
// Heuristics for selecting the stride ranges to collapse.
static int ValuesShouldBeCollapsedToStrideAverage(int a, int b) {
return abs(a - b) < 4;
@ -684,9 +604,8 @@ static int EncodeImageInternal(VP8LBitWriter* const bw,
if (histogram_image == NULL || histogram_symbols == NULL) goto Error;
// Calculate backward references from ARGB image.
if (!GetBackwardReferences(width, height, argb, quality,
use_color_cache, cache_bits, use_2d_locality,
&refs)) {
if (!VP8LGetBackwardReferences(width, height, argb, quality, cache_bits,
use_2d_locality, &refs)) {
goto Error;
}
// Build histogram image & symbols from backward references.