Bug fix for imread so images that are already grey-scale do not get flattened.

scikits/image/io/pil_imread.py

@@ -10,7 +10,9 @@ def imread(fname, flatten=False, dtype=None):
     fname : string
         Image file name, e.g. ``test.jpg``.
     flatten : bool
-        If true, convert the output to grey-scale.
+        If True, convert color images to grey-scale. If `dtype` is not given,
+        converted color images are returned as 32-bit float images.
+        Images that are already in grey-scale format are not converted.
     dtype : dtype, optional
         NumPy data-type specifier. If given, the returned image has this type.
         If None (default), the data-type is determined automatically.
@@ -32,6 +34,6 @@ def imread(fname, flatten=False, dtype=None):
                           " instructions.")
 
     im = Image.open(fname)
-    if flatten:
+    if flatten and not im.mode in ('1', 'L', 'I', 'F', 'I;16', 'I;16L', 'I;16B'):
         im = im.convert('F')
     return np.array(im, dtype=dtype)

scikits/image/io/tests/test_imread.py

@@ -4,7 +4,14 @@ import numpy as np
 from scikits.image import data_dir
 from scikits.image.io import imread
 
-def test_imread():
-    img = imread(os.path.join(data_dir, 'camera.png'), dtype=np.float32)
-    print img.dtype, type(img)
+def test_imread_flatten():
+    # a color image is flattened and returned as float32
+    img = imread(os.path.join(data_dir, 'color.png'), flatten=True)
     assert img.dtype == np.float32
+    img = imread(os.path.join(data_dir, 'camera.png'), flatten=True)
+    # check that flattening does not occur for an image that is grey already.
+    assert np.sctype2char(img.dtype) in np.typecodes['AllInteger']
+
+def test_imread_dtype():
+    img = imread(os.path.join(data_dir, 'camera.png'), dtype=np.float64)
+    assert img.dtype == np.float64