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Fixed bug with rounding pixels to palette

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This fixes a bug with rounding pixels to the nearest palette color. Specifically, there is a typo with computing the minimum distance from a palette color to a given cache box. This is causing palette colors to be incorrectly excluded from consideration.
This commit is contained in:
William Jacobs 2022-06-18 04:09:41 -04:00
parent 765d66c069
commit 9f9e26522e
8 changed files with 11 additions and 9 deletions
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Tests/images/palette_negative.png
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2
Tests/test_image_entropy.py
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@ -9,7 +9,7 @@ def test_entropy():
assert round(abs(entropy("L") - 7.063008716585465), 7) == 0 assert round(abs(entropy("L") - 7.063008716585465), 7) == 0
assert round(abs(entropy("I") - 7.063008716585465), 7) == 0 assert round(abs(entropy("I") - 7.063008716585465), 7) == 0
assert round(abs(entropy("F") - 7.063008716585465), 7) == 0 assert round(abs(entropy("F") - 7.063008716585465), 7) == 0
assert round(abs(entropy("P") - 5.0530452472519745), 7) == 0 assert round(abs(entropy("P") - 5.082506854662517), 7) == 0
assert round(abs(entropy("RGB") - 8.821286587714319), 7) == 0 assert round(abs(entropy("RGB") - 8.821286587714319), 7) == 0
assert round(abs(entropy("RGBA") - 7.42724306524488), 7) == 0 assert round(abs(entropy("RGBA") - 7.42724306524488), 7) == 0
assert round(abs(entropy("CMYK") - 7.4272430652448795), 7) == 0 assert round(abs(entropy("CMYK") - 7.4272430652448795), 7) == 0

2
Tests/test_image_getcolors.py
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@ -16,7 +16,7 @@ def test_getcolors():
assert getcolors("L") == 255 assert getcolors("L") == 255
assert getcolors("I") == 255 assert getcolors("I") == 255
assert getcolors("F") == 255 assert getcolors("F") == 255
assert getcolors("P") == 90 # fixed palette assert getcolors("P") == 96 # fixed palette
assert getcolors("RGB") is None assert getcolors("RGB") is None
assert getcolors("RGBA") is None assert getcolors("RGBA") is None
assert getcolors("CMYK") is None assert getcolors("CMYK") is None

2
Tests/test_image_histogram.py
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@ -10,7 +10,7 @@ def test_histogram():
assert histogram("L") == (256, 0, 662) assert histogram("L") == (256, 0, 662)
assert histogram("I") == (256, 0, 662) assert histogram("I") == (256, 0, 662)
assert histogram("F") == (256, 0, 662) assert histogram("F") == (256, 0, 662)
assert histogram("P") == (256, 0, 1871) assert histogram("P") == (256, 0, 1551)
assert histogram("RGB") == (768, 4, 675) assert histogram("RGB") == (768, 4, 675)
assert histogram("RGBA") == (1024, 0, 16384) assert histogram("RGBA") == (1024, 0, 16384)
assert histogram("CMYK") == (1024, 0, 16384) assert histogram("CMYK") == (1024, 0, 16384)

8
docs/releasenotes/9.2.0.rst
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@ -76,7 +76,9 @@ TODO
Other Changes Other Changes
============= =============
TODO Fixed bug with rounding pixels to palette
^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TODO Fixed a bug when rounding image pixels to palette colors. This affects the results of
``Image.quantize`` and of ``Image.convert`` when converting from mode "RGB" to "P",
"L", or "1", regardless of whether dithering is enabled.

6
src/libImaging/Palette.c
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@ -200,15 +200,15 @@ ImagingPaletteCacheUpdate(ImagingPalette palette, int r, int g, int b) {
/* Find min and max distances to any point in the box */ /* Find min and max distances to any point in the box */
r = palette->palette[i * 4 + 0]; r = palette->palette[i * 4 + 0];
tmin = (r < r0) ? RDIST(r, r1) : (r > r1) ? RDIST(r, r0) : 0; tmin = (r < r0) ? RDIST(r, r0) : (r > r1) ? RDIST(r, r1) : 0;
tmax = (r <= rc) ? RDIST(r, r1) : RDIST(r, r0); tmax = (r <= rc) ? RDIST(r, r1) : RDIST(r, r0);
g = palette->palette[i * 4 + 1]; g = palette->palette[i * 4 + 1];
tmin += (g < g0) ? GDIST(g, g1) : (g > g1) ? GDIST(g, g0) : 0; tmin += (g < g0) ? GDIST(g, g0) : (g > g1) ? GDIST(g, g1) : 0;
tmax += (g <= gc) ? GDIST(g, g1) : GDIST(g, g0); tmax += (g <= gc) ? GDIST(g, g1) : GDIST(g, g0);
b = palette->palette[i * 4 + 2]; b = palette->palette[i * 4 + 2];
tmin += (b < b0) ? BDIST(b, b1) : (b > b1) ? BDIST(b, b0) : 0; tmin += (b < b0) ? BDIST(b, b0) : (b > b1) ? BDIST(b, b1) : 0;
tmax += (b <= bc) ? BDIST(b, b1) : BDIST(b, b0); tmax += (b <= bc) ? BDIST(b, b1) : BDIST(b, b0);
dmin[i] = tmin; dmin[i] = tmin;