Correct background color when using P mode images with ImageOps.pad() (#9795)

Author: chuenchen309

Tests/test_imageops.py

@@ -171,6 +171,23 @@ def test_pad_round() -> None:
     assert new_im.getpixel((0, 2)) == 1
 
 
+def test_pad_palette() -> None:
+    with Image.open("Tests/images/p_16.tga") as im:
+        im_padded = ImageOps.pad(im, (im.width * 2, im.height), color=(255, 0, 0))
+        im_rgb = im_padded.convert("RGB")
+
+        # Verify that the left and right sides are now red
+        px = im_rgb.load()
+        assert px is not None
+        for y in range(im_rgb.height):
+            for x in range(im.width // 2):
+                assert px[x, y] == (255, 0, 0)
+                assert px[im_rgb.width - 1 - x, y] == (255, 0, 0)
+
+        im_cropped = im_rgb.crop((im.width * 0.5, 0, im.width * 1.5, im.height))
+        assert_image_equal(im_cropped, im.convert("RGB"))
+
+
 @pytest.mark.parametrize("mode", ("P", "PA"))
 def test_palette(mode: str) -> None:
     im = hopper(mode)

src/PIL/ImageOps.py

@@ -44,7 +44,9 @@ def _border(border: int | tuple[int, ...]) -> tuple[int, int, int, int]:
     return left, top, right, bottom
 
 
-def _color(color: str | int | tuple[int, ...], mode: str) -> int | tuple[int, ...]:
+def _color(
+    color: str | int | tuple[int, ...] | None, mode: str
+) -> int | tuple[int, ...] | None:
     if isinstance(color, str):
         from . import ImageColor
 
@@ -331,6 +333,23 @@ def cover(
     return image.resize(size, resample=method)
 
 
+def _new_with_fill(
+    image: Image.Image, size: tuple[int, int], fill: str | int | tuple[int, ...] | None
+) -> Image.Image:
+    color = _color(fill, image.mode)
+    if image.palette:
+        mode = image.palette.mode
+        palette = ImagePalette.ImagePalette(mode, image.getpalette(mode))
+        if isinstance(color, tuple) and len(color) in (3, 4):
+            color = palette.getcolor(color)
+    else:
+        palette = None
+    out = Image.new(image.mode, size, color)
+    if palette:
+        out.putpalette(palette.palette, mode)
+    return out
+
+
 def pad(
     image: Image.Image,
     size: tuple[int, int],
@@ -363,11 +382,7 @@ def pad(
     if resized.size == size:
         out = resized
     else:
-        out = Image.new(image.mode, size, color)
-        if resized.palette:
-            palette = resized.getpalette()
-            if palette is not None:
-                out.putpalette(palette)
+        out = _new_with_fill(resized, size, color)
         if resized.width != size[0]:
             x = round((size[0] - resized.width) * max(0, min(centering[0], 1)))
             out.paste(resized, (x, 0))
@@ -500,17 +515,7 @@ def expand(
     left, top, right, bottom = _border(border)
     width = left + image.size[0] + right
     height = top + image.size[1] + bottom
-    color = _color(fill, image.mode)
-    if image.palette:
-        mode = image.palette.mode
-        palette = ImagePalette.ImagePalette(mode, image.getpalette(mode))
-        if isinstance(color, tuple) and (len(color) == 3 or len(color) == 4):
-            color = palette.getcolor(color)
-    else:
-        palette = None
-    out = Image.new(image.mode, (width, height), color)
-    if palette:
-        out.putpalette(palette.palette, mode)
+    out = _new_with_fill(image, (width, height), fill)
     out.paste(image, (left, top))
     return out