Merge pull request #1790 from WarrenWeckesser/imread-indexed-png-alpha

FIX: imread w/PIL plugin no longer drops indexed PNG alpha channel

requirements.txt

@@ -3,5 +3,5 @@ numpy>=1.6.1
 scipy>=0.9.0
 six>=1.4
 networkx>=1.8
-pillow>=1.7.8
+pillow>=2.1.0
 dask[array]>=0.5.0

skimage/io/_plugins/pil_plugin.py

@@ -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

@@ -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)

tools/travis_before_install.sh

@@ -40,9 +40,6 @@ fi
 # test minimum requirements on 2.7
 if [[ $TRAVIS_PYTHON_VERSION == 2.7* ]]; then
     sed -i 's/>=/==/g' requirements.txt
-    # PIL instead of Pillow
-    sed -i 's/pillow.*/pil==1.1.7/g' requirements.txt
-    WHEELBINARIES=${WHEELBINARIES/pillow/pil}
 fi
 
 # create new empty venv