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BUG: io: imread in the PIL plugin drops indexed PNG alpha channel.

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When using the PIL plugin to read an indexed PNG file that has
an alpha channel, the alpha channel would be lost.
This commit is contained in:
Warren Weckesser
2015-11-18 13:55:57 -05:00
parent 2f3bc7f08d
commit 6b908c1bb1
3 changed files with 26 additions and 1 deletions
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skimage/data/foo3x5x4indexed.png
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skimage/io/_plugins/pil_plugin.py
+4 -1
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@@ -85,7 +85,10 @@ def pil_to_ndarray(im, dtype=None, img_num=None):
if grayscale:
frame = im.convert('L')
else:
frame = im.convert('RGB')
if im.format == 'PNG' and 'transparency' in im.info:
frame = im.convert('RGBA')
else:
frame = im.convert('RGB')
elif im.mode == '1':
frame = im.convert('L')
skimage/io/tests/test_pil.py
+22
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@@ -84,6 +84,28 @@ def test_imread_palette():
assert img.ndim == 3
def test_imread_index_png_with_alpha():
# The file `foo3x5x4indexed.png` was created with this array
# (3x5 is (height)x(width)):
data = np.array([[[127, 0, 255, 255],
[127, 0, 255, 255],
[127, 0, 255, 255],
[127, 0, 255, 255],
[127, 0, 255, 255]],
[[192, 192, 255, 0],
[192, 192, 255, 0],
[0, 0, 255, 0],
[0, 0, 255, 0],
[0, 0, 255, 0]],
[[0, 31, 255, 255],
[0, 31, 255, 255],
[0, 31, 255, 255],
[0, 31, 255, 255],
[0, 31, 255, 255]]], dtype=np.uint8)
img = imread(os.path.join(data_dir, 'foo3x5x4indexed.png'))
assert_array_equal(img, data)
def test_palette_is_gray():
gray = Image.open(os.path.join(data_dir, 'palette_gray.png'))
assert _palette_is_grayscale(gray)