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lossless: Allow copying from prev row in rle-mode.

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0.21 % compression density improvement for 1000 png corpus in
lossless mode

0.50 % compression density improvement for 1000 png corpus in
lossy mode

Change-Id: I14ee8c427ae5d3e116b0ee6695fcdea3321a319d
This commit is contained in:
Jyrki Alakuijala 2015-07-02 10:54:01 +00:00 committed by James Zern
parent f3a7a5bf76
commit 17eb609916
1 changed files with 25 additions and 30 deletions
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55
src/enc/backward_references.c
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@ -335,52 +335,47 @@ static WEBP_INLINE void AddSingleLiteral(uint32_t pixel, int use_color_cache,
BackwardRefsCursorAdd(refs, v);
}
static WEBP_INLINE void PushBackCopy(VP8LBackwardRefs* const refs, int length) {
while (length >= MAX_LENGTH) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, MAX_LENGTH));
length -= MAX_LENGTH;
}
if (length > 0) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, length));
}
}
static int BackwardReferencesRle(int xsize, int ysize,
const uint32_t* const argb,
int cache_bits, VP8LBackwardRefs* const refs) {
const int pix_count = xsize * ysize;
int match_len = 0;
int i;
int cc_init = 0;
int i, k;
const int use_color_cache = (cache_bits > 0);
VP8LColorCache hashers;
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) return 0;
if (use_color_cache && !VP8LColorCacheInit(&hashers, cache_bits)) {
return 0;
}
ClearBackwardRefs(refs);
// Add first pixel as literal.
AddSingleLiteral(argb[0], use_color_cache, &hashers, refs);
for (i = 1; i < pix_count; ++i) {
if (argb[i] == argb[i - 1]) {
++match_len;
} else {
const int kMinLength = 4;
if (match_len >= kMinLength) {
PushBackCopy(refs, match_len);
} else {
int k;
for(k = match_len; k >= 1; --k) {
AddSingleLiteral(argb[i - k], use_color_cache, &hashers, refs);
i = 1;
while (i < pix_count) {
const int max_len = MaxFindCopyLength(pix_count - i);
const int kMinLength = 4;
const int rle_len = FindMatchLength(argb + i, argb + i - 1, 0, max_len);
const int prev_row_len = (i < xsize) ? 0 :
FindMatchLength(argb + i, argb + i - xsize, 0, max_len);
if (rle_len >= prev_row_len && rle_len >= kMinLength) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, rle_len));
// We don't need to update the color cache here since it is always the
// same pixel being copied, and that does not change the color cache
// state.
i += rle_len;
} else if (prev_row_len >= kMinLength) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(xsize, prev_row_len));
if (use_color_cache) {
for (k = 0; k < prev_row_len; ++k) {
VP8LColorCacheInsert(&hashers, argb[i + k]);
}
}
match_len = 0;
i += prev_row_len;
} else {
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
i++;
}
}
PushBackCopy(refs, match_len);
if (cc_init) VP8LColorCacheClear(&hashers);
if (use_color_cache) VP8LColorCacheClear(&hashers);
return !refs->error_;
}