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Fix incorrect color blending for overlapping glyphs #7497

Merged
merged 21 commits into from Dec 24, 2023
Merged

Fix incorrect color blending for overlapping glyphs #7497

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f97570f
Blend colors with alpha when pasting
ZachNagengast Oct 27, 2023
49fd211
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Oct 27, 2023
76f758e
Merge branch 'main' into fix-alpha-for-overlapping-glyphs
radarhere Oct 27, 2023
bb0eff4
Update blending logic
ZachNagengast Nov 3, 2023
a7f805d
Merge branch 'fix-alpha-for-overlapping-glyphs' of ssh://github.com/Z…
ZachNagengast Nov 3, 2023
e1aaec3
Merge branch 'main' of ssh://github.com/python-pillow/Pillow into fix…
ZachNagengast Nov 3, 2023
b15b2d4
Update src/_imagingft.c
ZachNagengast Nov 7, 2023
fdecfca
Update gray glyph blending logic and tests
ZachNagengast Nov 7, 2023
8ecf2e9
Merge branch 'fix-alpha-for-overlapping-glyphs' of ssh://github.com/Z…
ZachNagengast Nov 7, 2023
11bea8f
Merge branch 'main' of ssh://github.com/python-pillow/Pillow into fix…
ZachNagengast Nov 7, 2023
d127600
Update test images for overlapping text
ZachNagengast Nov 7, 2023
0a33b30
Update caron_below_ttb test image
ZachNagengast Nov 12, 2023
29ca3fc
Update caron_below_ttb_lb test image
ZachNagengast Nov 12, 2023
f3b3442
add test for glyph alpha blending
nulano Nov 27, 2023
0cef9f2
fix drawing text alpha on RGBA image on big-endian platforms
nulano Nov 27, 2023
38992f6
Merge pull request #1 from nulano/fix-alpha-for-overlapping-glyphs
ZachNagengast Nov 27, 2023
9c60e85
Apply suggestions from code review
ZachNagengast Nov 27, 2023
78f78d2
Update src/_imagingft.c
ZachNagengast Nov 28, 2023
e800026
Update Tests/test_imagefont.py
ZachNagengast Dec 1, 2023
bd2977c
Update src/PIL/ImageDraw.py
ZachNagengast Dec 2, 2023
a6a612c
Merge branch 'main' into fix-alpha-for-overlapping-glyphs
radarhere Dec 2, 2023
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29 changes: 19 additions & 10 deletions src/_imagingft.c
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Expand Up @@ -1059,16 +1059,25 @@ font_render(FontObject *self, PyObject *args) {
if (color && bitmap.pixel_mode == FT_PIXEL_MODE_BGRA) {
/* paste color glyph */
for (k = x0; k < x1; k++) {
if (target[k * 4 + 3] < source[k * 4 + 3]) {
/* unpremultiply BGRa to RGBA */
target[k * 4 + 0] = CLIP8(
(255 * (int)source[k * 4 + 2]) / source[k * 4 + 3]);
target[k * 4 + 1] = CLIP8(
(255 * (int)source[k * 4 + 1]) / source[k * 4 + 3]);
target[k * 4 + 2] = CLIP8(
(255 * (int)source[k * 4 + 0]) / source[k * 4 + 3]);
target[k * 4 + 3] = source[k * 4 + 3];
}
float src_alpha = (float) source[k * 4 + 3] / 255.0;
float dst_alpha = (float) target[k * 4 + 3] / 255.0;
float out_alpha = src_alpha + dst_alpha * (1.0 - src_alpha);

/* unpremultiply BGRa to RGBA */
int src_red = source[k * 4 + 0];
int src_grn = source[k * 4 + 1];
int src_blu = source[k * 4 + 2];

int dst_blu = target[k * 4 + 0];
int dst_grn = target[k * 4 + 1];
int dst_red = target[k * 4 + 2];
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/* blend color values */
target[k * 4 + 0] = CLIP8((src_blu * src_alpha + dst_blu * dst_alpha * (1.0 - src_alpha)) / out_alpha);
target[k * 4 + 1] = CLIP8((src_grn * src_alpha + dst_grn * dst_alpha * (1.0 - src_alpha)) / out_alpha);
target[k * 4 + 2] = CLIP8((src_red * src_alpha + dst_red * dst_alpha * (1.0 - src_alpha)) / out_alpha);

target[k * 4 + 3] = CLIP8(out_alpha * 255.0);
}
} else if (bitmap.pixel_mode == FT_PIXEL_MODE_GRAY) {
if (color) {
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