Concatenate image collection

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 @@ def __len__(self):
     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.
@@ -307,3 +354,23 @@ def reload(self, n=None):
 
         """
         self.data = np.empty_like(self.data)
+
+    def concatenate(self):
+        """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 `ImageCollection` don't have identical shapes.
+        """
+        return concatenate_images(self)
+

skimage/io/tests/test_collection.py

@@ -23,9 +23,12 @@
 class TestImageCollection():
     pattern = [os.path.join(data_dir, pic) for pic in ['camera.png',
                                                        'color.png']]
+    pattern_matched = [os.path.join(data_dir, pic) for pic in 
+                                                    ['camera.png', 'moon.png']]
 
     def setUp(self):
         self.collection = ImageCollection(self.pattern)
+        self.collection_matched = ImageCollection(self.pattern_matched)
 
     def test_len(self):
         assert len(self.collection) == 2
@@ -59,6 +62,12 @@ def load_fn(x):
         ic = ImageCollection(load_pattern, load_func=load_fn)
         assert_equal(ic[1], (2, 'two'))
 
+    def test_concatenate(self):
+        ar = self.collection_matched.concatenate()
+        assert_equal(ar.shape, (len(self.collection_matched),) + 
+                                self.collection[0].shape)
+        assert_raises(ValueError, self.collection.concatenate)
+
 
 class TestMultiImage():
 
@@ -102,6 +111,12 @@ def set_mem(val):
             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()