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Fix BMP save of a P image with an empty palette #9746

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Fix BMP save of a P image with an empty palette #9746

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c78c84c
Fix BMP save of a P image with an empty palette
gaoflow Jun 30, 2026
10b57cf
Simplified code
radarhere Jul 28, 2026
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10 changes: 10 additions & 0 deletions Tests/test_file_bmp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,16 @@ def test_small_palette(tmp_path: Path) -> None:
assert reloaded.getpalette() == colors


def test_empty_palette(tmp_path: Path) -> None:
im = Image.new("P", (8, 8))

out = tmp_path / "temp.bmp"
im.save(out)

with Image.open(out) as reloaded:
assert_image_equal(im.convert("L"), reloaded)


def test_save_too_large(tmp_path: Path) -> None:
outfile = tmp_path / "temp.bmp"
with Image.new("RGB", (1, 1)) as im:
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3 changes: 2 additions & 1 deletion src/PIL/BmpImagePlugin.py
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Expand Up @@ -449,7 +449,8 @@ def _save(
elif im.mode == "L":
palette = b"".join(o8(i) * 3 + b"\x00" for i in range(256))
elif im.mode == "P":
palette = im.im.getpalette("RGB", "BGRX")
# Colors used should not be zero, as that is treated as the maximum
palette = im.im.getpalette("RGB", "BGRX") or b"\x00\x00\x00\x00"
colors = len(palette) // 4
else:
palette = None
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