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Fix alpha handling when flattening images for vector backends #32107

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Fix alpha handling when flattening images for vector backends #32107

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8 changes: 4 additions & 4 deletions lib/matplotlib/image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,7 @@ def composite_images(images, renderer, magnification=1.0):
if data is not None:
x *= magnification
y *= magnification
parts.append((data, x, y, image._get_scalar_alpha()))
parts.append((data, x, y))
bboxes.append(
Bbox([[x, y], [x + data.shape[1], y + data.shape[0]]]))

Expand All @@ -104,10 +104,10 @@ def composite_images(images, renderer, magnification=1.0):
output = np.zeros(
(int(bbox.height), int(bbox.width), 4), dtype=np.uint8)

for data, x, y, alpha in parts:
for data, x, y in parts:
trans = Affine2D().translate(x - bbox.x0, y - bbox.y0)
_image.resample(data, output, trans, _image.NEAREST,
resample=False, alpha=alpha)
# Agg resampler assumes data is not premultiplied when dtype is uint8
_image.resample(data, output, trans, _image.NEAREST, resample=False)

return output, bbox.x0 / magnification, bbox.y0 / magnification

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6 changes: 3 additions & 3 deletions lib/matplotlib/tests/baseline_images/test_image/image_composite_alpha.svg
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3 changes: 1 addition & 2 deletions lib/matplotlib/tests/test_image.py
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Expand Up @@ -617,8 +617,7 @@ def test_image_composite_background():
ax.set_xlim(0, 12)


@image_comparison(['image_composite_alpha'], remove_text=True, style='_classic_test',
tol=0.07)
@image_comparison(['image_composite_alpha'], remove_text=True, style='_classic_test')
def test_image_composite_alpha():
"""
Tests that the alpha value is recognized and correctly applied in the
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