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Convert grayscale images to RGB when saving AVIF with libavif < 1.3.0 #10263

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Merged
radarhere merged 3 commits into from
Oct 21, 2026
Merged

Convert grayscale images to RGB when saving AVIF with libavif < 1.3.0 #10263

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44b1aed
Convert grayscale images to RGB when saving AVIF with libavif < 1.3.0
lazerg Oct 20, 2026
4453528
Use list for parametrize
lazerg Oct 20, 2026
f197058
Merge previous test into new test
radarhere Oct 21, 2026
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16 changes: 10 additions & 6 deletions Tests/test_file_avif.py
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@
assert_image,
assert_image_similar,
assert_image_similar_tofile,
has_feature_version,
hopper,
skip_if_tsan,
skip_unless_feature,
Expand Down Expand Up @@ -133,13 +134,14 @@ def test_read(self) -> None:
image, "Tests/images/avif/hopper_avif_write.png", 11.5
)

@skip_unless_feature_version("avif", "1.3.0")
def test_write_l(self) -> None:
im = hopper("L")
reloaded = roundtrip(im)
@pytest.mark.parametrize("mode", ["1", "L", "I", "I;16", "F"])
def test_write_grayscale(self, mode: str) -> None:
im = hopper(mode)
reloaded: Image.Image = roundtrip(im)

assert reloaded.mode == "L"
assert_image_similar(reloaded, im, 1.69)
if not has_feature_version("avif", "1.3.0"):
reloaded = reloaded.convert("L")
assert_image_similar(reloaded, im.convert("L"), 1.69)

def test_write_rgb(self, tmp_path: Path) -> None:
"""
Expand Down Expand Up @@ -193,6 +195,8 @@ def test_encoder_finish_none_error(
"""Save should raise an OSError if AvifEncoder.finish returns None"""

class _mock_avif:
libavif_version = "1.3.0"

class AvifEncoder:
def __init__(self, *args: Any) -> None:
pass
Expand Down
9 changes: 7 additions & 2 deletions src/PIL/AvifImagePlugin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,11 @@ def _save(
advanced,
)

supported_modes = {"RGB", "RGBA"}
if tuple(int(v) for v in _avif.libavif_version.split(".")) >= (1, 3):
# AVIF_RGB_FORMAT_GRAY was only added in libavif 1.3.0
supported_modes.add("L")

# Add each frame
frame_idx = 0
frame_duration = 0
Expand All @@ -249,10 +254,10 @@ def _save(
for frame in ImageSequence.Iterator(ims):
# Make sure image mode is supported
rawmode = frame.mode
if ims.mode not in {"L", "RGB", "RGBA"}:
if ims.mode not in supported_modes:
if ims.has_transparency_data:
rawmode = "RGBA"
elif ims.mode in grayscale_modes:
elif ims.mode in grayscale_modes and "L" in supported_modes:
rawmode = "L"
else:
rawmode = "RGB"
Expand Down
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