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fix: "smearing" of gifs with transparent pixels #207

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Merged
salarkhan merged 2 commits into from
Dec 16, 2024
Merged

fix: "smearing" of gifs with transparent pixels #207

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0a99f59
dont use the midpoint of crushed colors
salarkhan Dec 13, 2024
4ce6cdd
actually, only worry about this scenario in extreme colors (pure whit…
salarkhan Dec 16, 2024
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34 changes: 19 additions & 15 deletions giflib.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -862,24 +862,28 @@ static bool giflib_encoder_render_frame(giflib_encoder e,
int least_dist = INT_MAX;
int best_color = 0;
if (!(e->palette_lookup[crushed].present)) {
// calculate the best palette entry based on the midpoint of the crushed colors
// what this means is that we drop the crushed bits (& 0xf8)
// and then OR the highest-order crushed bit back in, which is approx midpoint
uint32_t R_center = (R & 0xf8) | 4;
uint32_t G_center = (G & 0xf8) | 4;
uint32_t B_center = (B & 0xf8) | 4;

// we're calculating the best, so keep track of which palette entry has least
// distance
int count = color_map->ColorCount;
for (int i = 0; i < count; i++) {
if (i == transparency_index) {

bool is_extreme_color = (R > 240 && G > 240 && B > 240) || (R < 15 && G < 15 && B < 15);

// calculate the best palette entry based on the midpoint of the crushed colors.
// what this means is that we drop the crushed bits (& 0xf8)
// and then OR the highest-order crushed bit back in, which is approx midpoint.
// for extreme colors, use actual values
uint32_t R_compare = is_extreme_color ? R : (R & 0xf8) | 4;
uint32_t G_compare = is_extreme_color ? G : (G & 0xf8) | 4;
uint32_t B_compare = is_extreme_color ? B : (B & 0xf8) | 4;

// we're calculating the best, so keep track of which
// palette entry has least distance
int count = color_map->ColorCount;
for (int i = 0; i < count; i++) {
if (i == transparency_index) {
// this index doesn't point to an actual color
continue;
}
int dist = rgb_distance(R_center,
G_center,
B_center,
int dist = rgb_distance(R_compare,
G_compare,
B_compare,
color_map->Colors[i].Red,
color_map->Colors[i].Green,
color_map->Colors[i].Blue);
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