Add concatenate() support for MultiImage

Previously we added the ImageCollection.concatenate function. This
updates MultiImage to have the same functionality, and moves the grunt
work to an outside function to avoid repetition.

skimage/io/collection.py

@@ -2,13 +2,42 @@
 
 from __future__ import with_statement
 
-__all__ = ['MultiImage', 'ImageCollection', 'imread']
+__all__ = ['MultiImage', 'ImageCollection', 'imread', 'concatenate_images']
 
 from glob import glob
 
 import numpy as np
 from ._io import imread
 
+def concatenate_images(ic):
+    """Concatenate all images in the image collection into an array.
+
+    Parameters
+    ----------
+    ic: an iterable of images (including ImageCollection and MultiImage)
+        The images to be concatenated.
+
+    Returns
+    -------
+    ar : np.ndarray
+        An array having one more dimension than the images in `ic`.
+
+    See Also
+    --------
+    `ImageCollection.concatenate`, `MultiImage.concatenate`
+
+    Raises
+    ------
+    ValueError
+        If images in `ic` don't have identical shapes.
+    """
+    all_images = [img[np.newaxis, ...] for img in ic]
+    try:
+        ar = np.concatenate(all_images)
+    except ValueError:
+        raise ValueError('Image dimensions must agree.')
+    return ar
+
 
 class MultiImage(object):
     """A class containing a single multi-frame image.
@@ -142,6 +171,24 @@ class MultiImage(object):
     def __str__(self):
         return str(self.filename) + ' [%s frames]' % self._numframes
 
+    def concatenate(self):
+        """Concatenate all images in the multi-image into an array.
+
+        Returns
+        -------
+        ar : np.ndarray
+            An array having one more dimension than the images in `self`.
+
+        See Also
+        --------
+        `concatenate_images`
+
+        Raises
+        ------
+        ValueError
+            If images in the `MultiImage` don't have identical shapes.
+        """
+        return concatenate_images(self)
 
 class ImageCollection(object):
     """Load and manage a collection of image files.
@@ -309,21 +356,21 @@ class ImageCollection(object):
         self.data = np.empty_like(self.data)
 
     def concatenate(self):
-        """Concatenate all images in the collection on a new axis.
+        """Concatenate all images in the collection into an array.
 
         Returns
         -------
         ar : np.ndarray
             An array having one more dimension than the images in `self`.
 
+        See Also
+        --------
+        `concatenate_images`
+
         Raises
         ------
         ValueError
-            If images in the collection don't have identical shapes.
+            If images in the `ImageCollection` don't have identical shapes.
         """
-        all_images = [img[np.newaxis, ...] for img in self]
-        try:
-            ar = np.concatenate(all_images)
-        except ValueError:
-            raise ValueError('Image dimensions must agree.')
-        return ar
+        return concatenate_images(self)
+

skimage/io/tests/test_collection.py

@@ -111,6 +111,12 @@ class TestMultiImage():
             self.img.conserve_memory = val
         assert_raises(AttributeError, set_mem, True)
 
+    @skipif(not PIL_available)
+    def test_concatenate(self):
+        ar = self.img.concatenate()
+        assert_equal(ar.shape, (len(self.img),) + 
+                                self.img[0].shape)
+
 
 if __name__ == "__main__":
     run_module_suite()