Added rounding when converting P and PA #5824
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radarhere
commented
Nov 9, 2021
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| im_l = im.convert("L") | ||
| assert im_l.info["transparency"] == 0 # undone | ||
| assert im_l.info["transparency"] == 1 # undone |
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The first palette entry is (0, 1, 2). (0*299 + 1*587 + 2*114) / 1000 = 0.815, so this is now rounded to 1.
radarhere
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homm
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Nov 9, 2021
src/libImaging/Convert.c
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| /* FIXME: precalculate greyscale palette? */ | ||
| for (x = 0; x < xsize; x++) { | ||
| *out++ = L(&palette[in[x] * 4]) / 1000; | ||
| *out++ = round(L(&palette[in[x] * 4]) / 1000.0); |
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Floating point arithmetic slower than integer. It's better to use L24 macro here, it already contains rounding.
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Thanks. I've updated the commit.
radarhere
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radarhere
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Resolves #5728
The issue discusses a pixel in an image with the palette value
(177, 175, 175), and asks why converting from P to L doesn't convert it to 176. That conversion uses the L macro -Pillow/src/libImaging/Convert.c
Lines 1012 to 1016 in a3d1e2f
Pillow/src/libImaging/Convert.c
Line 43 in a3d1e2f
Applying the L macro,
(177*299 + 175*587 + 175*114) / 1000= 175.598Except the
p2lcode above rounds it down. This PR applies proper rounding to bring it to 176.