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Note that the fill behaviour only affects libwebp >= 0.5

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This commit is contained in:
Andrew Murray 2022-11-19 17:12:51 +11:00
parent 96a4d98abc
commit 7e5e843d5c
1 changed files with 20 additions and 25 deletions
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45
Tests/test_file_webp_alpha.py
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@ -97,38 +97,33 @@ def test_write_rgba(tmp_path):
assert_image_similar(image, pil_image, 1.0) assert_image_similar(image, pil_image, 1.0)
def test_write_rgba_keep_transparent(tmp_path): def test_keep_rgb_values_when_transparent(tmp_path):
""" """
Can we write a RGBA mode file to WebP while preserving Saving transparent pixels should retain their original RGB values
the transparent RGB without error. when using the "exact" parameter.
Does it have the bits we expect?
""" """
temp_output_file = str(tmp_path / "temp.webp") image = hopper("RGB")
input_image = hopper("RGB") # create a copy of the image
# make a copy of the image # with the left half transparent
output_image = input_image.copy() half_transparent_image = image.copy()
# make a single channel image with the same size as input_image new_alpha = Image.new("L", (128, 128), 255)
new_alpha = Image.new("L", input_image.size, 255) new_alpha.paste(0, (0, 0, 64, 128))
# make the left half transparent half_transparent_image.putalpha(new_alpha)
new_alpha.paste((0,), (0, 0, new_alpha.size[0] // 2, new_alpha.size[1]))
# putalpha on output_image
output_image.putalpha(new_alpha)
# now save with transparent area preserved. # save with transparent area preserved
output_image.save(temp_output_file, "WEBP", exact=True, lossless=True) temp_file = str(tmp_path / "temp.webp")
# even though it is lossless, if we don't put exact=True, the transparent half_transparent_image.save(temp_file, exact=True, lossless=True)
# area will be filled with black (or something more conducive to compression)
with Image.open(temp_output_file) as image: with Image.open(temp_file) as reloaded:
image.load() assert reloaded.mode == "RGBA"
assert reloaded.format == "WEBP"
assert image.mode == "RGBA" # even though it is lossless, if we don't use exact=True
assert image.format == "WEBP" # in libwebp >= 0.5, the transparent area will be filled with black
image.load() # (or something more conducive to compression)
image = image.convert("RGB") assert_image_similar(reloaded.convert("RGB"), image, 1)
assert_image_similar(image, input_image, 1.0)
def test_write_unsupported_mode_PA(tmp_path): def test_write_unsupported_mode_PA(tmp_path):