Updates for ImagePalette channel order

Tests/test_file_gif.py

@@ -833,7 +833,7 @@ def test_palette_save_ImagePalette(tmp_path):
 
     with Image.open(out) as reloaded:
         im.putpalette(palette)
-        assert_image_equal(reloaded, im)
+        assert_image_equal(reloaded.convert("RGB"), im.convert("RGB"))
 
 
 def test_save_I(tmp_path):

Tests/test_image_putpalette.py

@@ -2,7 +2,7 @@
 
 from PIL import Image, ImagePalette
 
-from .helper import assert_image_equal, hopper
+from .helper import assert_image_equal, assert_image_equal_tofile, hopper
 
 
 def test_putpalette():
@@ -36,9 +36,15 @@ def palette(mode):
 def test_imagepalette():
     im = hopper("P")
     im.putpalette(ImagePalette.negative())
+    assert_image_equal_tofile(im.convert("RGB"), "Tests/images/palette_negative.png")
+
     im.putpalette(ImagePalette.random())
+
     im.putpalette(ImagePalette.sepia())
+    assert_image_equal_tofile(im.convert("RGB"), "Tests/images/palette_sepia.png")
+
     im.putpalette(ImagePalette.wedge())
+    assert_image_equal_tofile(im.convert("RGB"), "Tests/images/palette_wedge.png")
 
 
 def test_putpalette_with_alpha_values():

docs/reference/ImagePalette.rst

@@ -9,10 +9,6 @@ represent the color palette of palette mapped images.
 
 .. note::
 
-    This module was never well-documented. It hasn't changed since 2001,
-    though, so it's probably safe for you to read the source code and puzzle
-    out the internals if you need to.
-
     The :py:class:`~PIL.ImagePalette.ImagePalette` class has several methods,
     but they are all marked as "experimental." Read that as you will. The
     ``[source]`` link is there for a reason.

src/PIL/GifImagePlugin.py

@@ -396,15 +396,7 @@ def _normalize_palette(im, palette, info):
         if isinstance(palette, (bytes, bytearray, list)):
             source_palette = bytearray(palette[:768])
         if isinstance(palette, ImagePalette.ImagePalette):
-            source_palette = bytearray(
-                itertools.chain.from_iterable(
-                    zip(
-                        palette.palette[:256],
-                        palette.palette[256:512],
-                        palette.palette[512:768],
-                    )
-                )
-            )
+            source_palette = bytearray(palette.palette)
 
     if im.mode == "P":
         if not source_palette:

src/PIL/ImagePalette.py

@@ -25,12 +25,12 @@ class ImagePalette:
     """
     Color palette for palette mapped images
 
-    :param mode: The mode to use for the Palette. See:
+    :param mode: The mode to use for the palette. See:
         :ref:`concept-modes`. Defaults to "RGB"
     :param palette: An optional palette. If given, it must be a bytearray,
-        an array or a list of ints between 0-255. The list must be aligned
-        by channel (All R values must be contiguous in the list before G
-        and B values.) Defaults to 0 through 255 per channel.
+        an array or a list of ints between 0-255. The list must consist of
+        all channels for one color followed by the next color (e.g. RGBRGBRGB).
+        Defaults to an empty palette.
     :param size: An optional palette size. If given, an error is raised
         if ``palette`` is not of equal length.
     """
@@ -204,9 +204,9 @@ def make_gamma_lut(exp):
 
 
 def negative(mode="RGB"):
-    palette = list(range(256))
+    palette = list(range(256 * len(mode)))
     palette.reverse()
-    return ImagePalette(mode, palette * len(mode))
+    return ImagePalette(mode, [i // len(mode) for i in palette])
 
 
 def random(mode="RGB"):
@@ -219,15 +219,13 @@ def random(mode="RGB"):
 
 
 def sepia(white="#fff0c0"):
-    r, g, b = ImageColor.getrgb(white)
-    r = make_linear_lut(0, r)
-    g = make_linear_lut(0, g)
-    b = make_linear_lut(0, b)
-    return ImagePalette("RGB", r + g + b)
+    bands = [make_linear_lut(0, band) for band in ImageColor.getrgb(white)]
+    return ImagePalette("RGB", [bands[i % 3][i // 3] for i in range(256 * 3)])
 
 
 def wedge(mode="RGB"):
-    return ImagePalette(mode, list(range(256)) * len(mode))
+    palette = list(range(256 * len(mode)))
+    return ImagePalette(mode, [i // len(mode) for i in palette])
 
 
 def load(filename):