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Fix rounding error on RGB to L conversion #4320

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Jan 1, 2020
Merged

Fix rounding error on RGB to L conversion #4320

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d68147c
Fix rounding error on RGB to L conversion
homm Dec 31, 2019
fa1deca
Fix wrong tests
homm Dec 31, 2019
038f9da
bring ImageColor.getcolor into line with Convert.c implementation
homm Dec 31, 2019
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Binary file modified Tests/images/imagedraw_floodfill_L.png
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Binary file modified Tests/images/imagedraw_polygon_kite_L.png
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6 changes: 3 additions & 3 deletions Tests/test_image_entropy.py
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,9 @@ def entropy(mode):
return hopper(mode).entropy()

self.assertAlmostEqual(entropy("1"), 0.9138803254693582)
self.assertAlmostEqual(entropy("L"), 7.06650513081286)
self.assertAlmostEqual(entropy("I"), 7.06650513081286)
self.assertAlmostEqual(entropy("F"), 7.06650513081286)
self.assertAlmostEqual(entropy("L"), 7.063008716585465)
self.assertAlmostEqual(entropy("I"), 7.063008716585465)
self.assertAlmostEqual(entropy("F"), 7.063008716585465)
self.assertAlmostEqual(entropy("P"), 5.0530452472519745)
self.assertAlmostEqual(entropy("RGB"), 8.821286587714319)
self.assertAlmostEqual(entropy("RGBA"), 7.42724306524488)
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6 changes: 3 additions & 3 deletions Tests/test_image_getdata.py
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Expand Up @@ -20,9 +20,9 @@ def getdata(mode):
return data[0], len(data), len(list(data))

self.assertEqual(getdata("1"), (0, 960, 960))
self.assertEqual(getdata("L"), (16, 960, 960))
self.assertEqual(getdata("I"), (16, 960, 960))
self.assertEqual(getdata("F"), (16.0, 960, 960))
self.assertEqual(getdata("L"), (17, 960, 960))
self.assertEqual(getdata("I"), (17, 960, 960))
self.assertEqual(getdata("F"), (17.0, 960, 960))
self.assertEqual(getdata("RGB"), ((11, 13, 52), 960, 960))
self.assertEqual(getdata("RGBA"), ((11, 13, 52, 255), 960, 960))
self.assertEqual(getdata("CMYK"), ((244, 242, 203, 0), 960, 960))
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8 changes: 4 additions & 4 deletions Tests/test_image_getextrema.py
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Expand Up @@ -9,14 +9,14 @@ def extrema(mode):
return hopper(mode).getextrema()

self.assertEqual(extrema("1"), (0, 255))
self.assertEqual(extrema("L"), (0, 255))
self.assertEqual(extrema("I"), (0, 255))
self.assertEqual(extrema("F"), (0, 255))
self.assertEqual(extrema("L"), (1, 255))
self.assertEqual(extrema("I"), (1, 255))
self.assertEqual(extrema("F"), (1, 255))
self.assertEqual(extrema("P"), (0, 225)) # fixed palette
self.assertEqual(extrema("RGB"), ((0, 255), (0, 255), (0, 255)))
self.assertEqual(extrema("RGBA"), ((0, 255), (0, 255), (0, 255), (255, 255)))
self.assertEqual(extrema("CMYK"), ((0, 255), (0, 255), (0, 255), (0, 0)))
self.assertEqual(extrema("I;16"), (0, 255))
self.assertEqual(extrema("I;16"), (1, 255))

def test_true_16(self):
with Image.open("Tests/images/16_bit_noise.tif") as im:
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6 changes: 3 additions & 3 deletions Tests/test_image_histogram.py
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Expand Up @@ -8,9 +8,9 @@ def histogram(mode):
return len(h), min(h), max(h)

self.assertEqual(histogram("1"), (256, 0, 10994))
self.assertEqual(histogram("L"), (256, 0, 638))
self.assertEqual(histogram("I"), (256, 0, 638))
self.assertEqual(histogram("F"), (256, 0, 638))
self.assertEqual(histogram("L"), (256, 0, 662))
self.assertEqual(histogram("I"), (256, 0, 662))
self.assertEqual(histogram("F"), (256, 0, 662))
self.assertEqual(histogram("P"), (256, 0, 1871))
self.assertEqual(histogram("RGB"), (768, 4, 675))
self.assertEqual(histogram("RGBA"), (1024, 0, 16384))
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6 changes: 3 additions & 3 deletions Tests/test_imagecolor.py
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Expand Up @@ -165,20 +165,20 @@ def test_rounding_errors(self):

self.assertEqual(0, ImageColor.getcolor("black", "L"))
self.assertEqual(255, ImageColor.getcolor("white", "L"))
self.assertEqual(162, ImageColor.getcolor("rgba(0, 255, 115, 33)", "L"))
self.assertEqual(163, ImageColor.getcolor("rgba(0, 255, 115, 33)", "L"))
Image.new("L", (1, 1), "white")

self.assertEqual(0, ImageColor.getcolor("black", "1"))
self.assertEqual(255, ImageColor.getcolor("white", "1"))
# The following test is wrong, but is current behavior
# The correct result should be 255 due to the mode 1
self.assertEqual(162, ImageColor.getcolor("rgba(0, 255, 115, 33)", "1"))
self.assertEqual(163, ImageColor.getcolor("rgba(0, 255, 115, 33)", "1"))
# Correct behavior
# self.assertEqual(
# 255, ImageColor.getcolor("rgba(0, 255, 115, 33)", "1"))
Image.new("1", (1, 1), "white")

self.assertEqual((0, 255), ImageColor.getcolor("black", "LA"))
self.assertEqual((255, 255), ImageColor.getcolor("white", "LA"))
self.assertEqual((162, 33), ImageColor.getcolor("rgba(0, 255, 115, 33)", "LA"))
self.assertEqual((163, 33), ImageColor.getcolor("rgba(0, 255, 115, 33)", "LA"))
Image.new("LA", (1, 1), "white")
4 changes: 3 additions & 1 deletion src/PIL/ImageColor.py
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Expand Up @@ -134,7 +134,9 @@ def getcolor(color, mode):

if Image.getmodebase(mode) == "L":
r, g, b = color
color = (r * 299 + g * 587 + b * 114) // 1000
# ITU-R Recommendation 601-2 for nonlinear RGB
# scaled to 24 bits to match the convert's implementation.
color = (r * 19595 + g * 38470 + b * 7471 + 0x8000) >> 16
if mode[-1] == "A":
return (color, alpha)
else:
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3 changes: 2 additions & 1 deletion src/libImaging/Convert.c
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Expand Up @@ -44,7 +44,8 @@
#define L(rgb)\
((INT32) (rgb)[0]*299 + (INT32) (rgb)[1]*587 + (INT32) (rgb)[2]*114)
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@radarhere radarhere Dec 31, 2019 •
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If you've changed ImageColor, shouldn't this be changed as well for consistency?

Pillow/src/PIL/ImageColor.py

Line 137 in fa1deca

color = (r * 299 + g * 587 + b * 114 + 500) // 1000

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@homm homm Dec 31, 2019 •
edited

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Not the "L" macro itself should be fixed. This macro is used for F mode for example, where no rounding needed. Instead, every place where "L" is used should be analyzed. This is a bit more work that needs more attention and I haven't much time today to do this before the release.

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Actually, I've fixed ImageColor.getcolor implementation.

#define L24(rgb)\
((rgb)[0]*19595 + (rgb)[1]*38470 + (rgb)[2]*7471)
((rgb)[0]*19595 + (rgb)[1]*38470 + (rgb)[2]*7471 + 0x8000)


#ifndef round
double round(double x) {
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