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Set all transparent colors to be equal in quantize() #5282

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merged 1 commit into from Mar 31, 2021
Merged

Set all transparent colors to be equal in quantize() #5282

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10 changes: 10 additions & 0 deletions Tests/test_image_quantize.py
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Expand Up @@ -74,3 +74,13 @@ def test_quantize_dither_diff():
nodither = image.quantize(dither=0, palette=palette)

assert dither.tobytes() != nodither.tobytes()


def test_transparent_colors_equal():
im = Image.new("RGBA", (1, 2), (0, 0, 0, 0))
px = im.load()
px[0, 1] = (255, 255, 255, 0)

converted = im.quantize()
converted_px = converted.load()
assert converted_px[0, 0] == converted_px[0, 1]
23 changes: 17 additions & 6 deletions src/libImaging/Quant.c
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Expand Up @@ -1688,9 +1688,26 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
} else if (!strcmp(im->mode, "RGB") || !strcmp(im->mode, "RGBA")) {
/* true colour */

withAlpha = !strcmp(im->mode, "RGBA");
int transparency = 0;
unsigned char r, g, b;
for (i = y = 0; y < im->ysize; y++) {
for (x = 0; x < im->xsize; x++, i++) {
p[i].v = im->image32[y][x];
if (withAlpha && p[i].c.a == 0) {
if (transparency == 0) {
transparency = 1;
r = p[i].c.r;
g = p[i].c.g;
b = p[i].c.b;
} else {
/* Set all subsequent transparent pixels
to the same colour as the first */
p[i].c.r = r;
p[i].c.g = g;
p[i].c.b = b;
}
}
}
}

Expand Down Expand Up @@ -1725,9 +1742,6 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
kmeans);
break;
case 2:
if (!strcmp(im->mode, "RGBA")) {
withAlpha = 1;
}
result = quantize_octree(
p,
im->xsize * im->ysize,
Expand All @@ -1739,9 +1753,6 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
break;
case 3:
#ifdef HAVE_LIBIMAGEQUANT
if (!strcmp(im->mode, "RGBA")) {
withAlpha = 1;
}
result = quantize_pngquant(
p,
im->xsize,
Expand Down