Added rounding when converting P and PA #5824
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radarhere
reviewed
Nov 9, 2021
| @@ -93,7 +93,7 @@ def test_trns_p(tmp_path): | |||
| f = str(tmp_path / "temp.png") | |||
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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
reviewed
Nov 9, 2021
src/libImaging/Convert.c
Outdated
| @@ -1013,7 +1013,7 @@ p2l(UINT8 *out, const UINT8 *in, int xsize, const UINT8 *palette) { | |||
| int x; | |||
| /* 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.