Describe plugins using .ini files, so that we don't need to import them to know their capabilities.

scikits/image/io/_plugins/pil_plugin.py

@@ -5,50 +5,45 @@ import numpy as np
 
 try:
     from PIL import Image
-    has_pil = True
 except ImportError:
-    has_pil = False
+    print 'Could not load Python Imaging Library'
+else:
+    def imread(fname, as_grey=False, dtype=None):
+        """Load an image from file.
 
-def imread(fname, as_grey=False, dtype=None):
-    """Load an image from file.
+        """
+        im = Image.open(fname)
+        if im.mode == 'P':
+            if palette_is_grayscale(im):
+                im = im.convert('L')
+            else:
+                im = im.convert('RGB')
 
-    """
-    im = Image.open(fname)
-    if im.mode == 'P':
-        if palette_is_grayscale(im):
-            im = im.convert('L')
-        else:
-            im = im.convert('RGB')
+        if as_grey and not \
+               im.mode in ('1', 'L', 'I', 'F', 'I;16', 'I;16L', 'I;16B'):
+            im = im.convert('F')
 
-    if as_grey 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)
 
-    return np.array(im, dtype=dtype)
+    def palette_is_grayscale(pil_image):
+        """Return True if PIL image in palette mode is grayscale.
 
-def palette_is_grayscale(pil_image):
-    """Return True if PIL image in palette mode is grayscale.
+        Parameters
+        ----------
+        pil_image : PIL image
+            PIL Image that is in Palette mode.
 
-    Parameters
-    ----------
-    pil_image : PIL image
-        PIL Image that is in Palette mode.
-
-    Returns
-    -------
-    is_grayscale : bool
-        True if all colors in image palette are gray.
-    """
-    assert pil_image.mode == 'P'
-    # get palette as an array with R, G, B columns
-    palette = np.asarray(pil_image.getpalette()).reshape((256, 3))
-    # Not all palette colors are used; unused colors have junk values.
-    start, stop = pil_image.getextrema()
-    valid_palette = palette[start:stop]
-    # Image is grayscale if channel differences (R - G and G - B)
-    # are all zero.
-    return np.allclose(np.diff(valid_palette), 0)
-
-
-if has_pil:
-    plugin.register('pil', read=imread)
+        Returns
+        -------
+        is_grayscale : bool
+            True if all colors in image palette are gray.
+        """
+        assert pil_image.mode == 'P'
+        # get palette as an array with R, G, B columns
+        palette = np.asarray(pil_image.getpalette()).reshape((256, 3))
+        # Not all palette colors are used; unused colors have junk values.
+        start, stop = pil_image.getextrema()
+        valid_palette = palette[start:stop]
+        # Image is grayscale if channel differences (R - G and G - B)
+        # are all zero.
+        return np.allclose(np.diff(valid_palette), 0)