Merge pull request #6377 from btrekkie/fix-round-to-palette

Fixed bug with rounding pixels to palette

Tests/test_image_entropy.py

@@ -9,7 +9,7 @@ def test_entropy():
     assert round(abs(entropy("L") - 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("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("RGBA") - 7.42724306524488), 7) == 0
     assert round(abs(entropy("CMYK") - 7.4272430652448795), 7) == 0

Tests/test_image_getcolors.py

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

Tests/test_image_histogram.py

@@ -10,7 +10,7 @@ def test_histogram():
     assert histogram("L") == (256, 0, 662)
     assert histogram("I") == (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("RGBA") == (1024, 0, 16384)
     assert histogram("CMYK") == (1024, 0, 16384)

Tests/test_image_quantize.py

@@ -65,6 +65,22 @@ def test_quantize_no_dither():
     assert converted.palette.palette == palette.palette.palette
 
 
+def test_quantize_no_dither2():
+    im = Image.new("RGB", (9, 1))
+    im.putdata(list((p,) * 3 for p in range(0, 36, 4)))
+
+    palette = Image.new("P", (1, 1))
+    data = (0, 0, 0, 32, 32, 32)
+    palette.putpalette(data)
+    quantized = im.quantize(dither=Image.Dither.NONE, palette=palette)
+
+    assert tuple(quantized.palette.palette) == data
+
+    px = quantized.load()
+    for x in range(9):
+        assert px[x, 0] == (0 if x < 5 else 1)
+
+
 def test_quantize_dither_diff():
     image = hopper()
     with Image.open("Tests/images/caption_6_33_22.png") as palette:

src/libImaging/Palette.c

@@ -200,15 +200,15 @@ ImagingPaletteCacheUpdate(ImagingPalette palette, int r, int g, int b) {
 
         /* Find min and max distances to any point in the box */
         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);
 
         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);
 
         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);
 
         dmin[i] = tmin;