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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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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);