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Put 0 at the end of a palette and do not store it.

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This only applies to kSortedDefault and kMinimizeDelta.

Change-Id: I9d4178406ed2ef91c5c55f0a1919cfc6605fedf9
This commit is contained in:
Vincent Rabaud 2024-06-25 14:46:05 +02:00
parent 0ec80aef3d
commit c4af79d053
3 changed files with 27 additions and 7 deletions
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17
src/enc/vp8l_enc.c
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@ -1419,17 +1419,24 @@ static WebPEncodingError EncodePalette(VP8LBitWriter* const bw, int low_effort,
uint32_t tmp_palette[MAX_PALETTE_SIZE];
const int palette_size = enc->palette_size_;
const uint32_t* const palette = enc->palette_;
// If the last element is 0, do not store it and count on automatic palette
// 0-filling. This can only happen if there is no pixel packing, hence if
// there are strictly more than 16 colors (after 0 is removed).
const uint32_t encoded_palette_size =
(enc->palette_[palette_size - 1] == 0 && palette_size > 17)
? palette_size - 1
: palette_size;
VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
VP8LPutBits(bw, COLOR_INDEXING_TRANSFORM, 2);
assert(palette_size >= 1 && palette_size <= MAX_PALETTE_SIZE);
VP8LPutBits(bw, palette_size - 1, 8);
for (i = palette_size - 1; i >= 1; --i) {
VP8LPutBits(bw, encoded_palette_size - 1, 8);
for (i = encoded_palette_size - 1; i >= 1; --i) {
tmp_palette[i] = VP8LSubPixels(palette[i], palette[i - 1]);
}
tmp_palette[0] = palette[0];
return EncodeImageNoHuffman(bw, tmp_palette, &enc->hash_chain_,
&enc->refs_[0], palette_size, 1, /*quality=*/20,
low_effort, enc->pic_, percent_range, percent);
return EncodeImageNoHuffman(
bw, tmp_palette, &enc->hash_chain_, &enc->refs_[0], encoded_palette_size,
1, /*quality=*/20, low_effort, enc->pic_, percent_range, percent);
}
// -----------------------------------------------------------------------------

15
src/utils/palette.c
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@ -191,6 +191,12 @@ static void PaletteSortMinimizeDeltas(const uint32_t* const palette_sorted,
// Find greedily always the closest color of the predicted color to minimize
// deltas in the palette. This reduces storage needs since the
// palette is stored with delta encoding.
if (num_colors > 17) {
if (palette[0] == 0) {
--num_colors;
SwapColor(&palette[num_colors], &palette[0]);
}
}
for (i = 0; i < num_colors; ++i) {
int best_ix = i;
uint32_t best_score = ~0U;
@ -384,8 +390,13 @@ int PaletteSort(PaletteSorting method, const struct WebPPicture* const pic,
uint32_t* const palette) {
switch (method) {
case kSortedDefault:
// Nothing to do, we have already sorted the palette.
memcpy(palette, palette_sorted, num_colors * sizeof(*palette));
if (palette_sorted[0] == 0 && num_colors > 17) {
memcpy(palette, palette_sorted + 1,
(num_colors - 1) * sizeof(*palette_sorted));
palette[num_colors - 1] = 0;
} else {
memcpy(palette, palette_sorted, num_colors * sizeof(*palette));
}
return 1;
case kMinimizeDelta:
PaletteSortMinimizeDeltas(palette_sorted, num_colors, palette);

2
src/utils/palette.h
View File

@ -53,6 +53,8 @@ int GetColorPalette(const struct WebPPicture* const pic,
// Sorts the palette according to the criterion defined by 'method'.
// 'palette_sorted' is the input palette sorted lexicographically, as done in
// PrepareMapToPalette. Returns 0 on memory allocation error.
// For kSortedDefault and kMinimizeDelta methods, 0 (if present) is set as the
// last element to optimize later storage.
int PaletteSort(PaletteSorting method, const struct WebPPicture* const pic,
const uint32_t* const palette_sorted, uint32_t num_colors,
uint32_t* const palette);