Add short doc string example

skimage/measure/block.py

@@ -24,6 +24,34 @@ def block_reduce(image, block_size, func=np.sum, cval=0):
     image : ndarray
         Down-sampled image with same number of dimensions as input image.
 
+    Examples
+    --------
+    >>> from skimage.measure import block_reduce
+    >>> image = np.arange(3*3*4).reshape(3, 3, 4)
+    >>> image
+    array([[[ 0,  1,  2,  3],
+            [ 4,  5,  6,  7],
+            [ 8,  9, 10, 11]],
+
+           [[12, 13, 14, 15],
+            [16, 17, 18, 19],
+            [20, 21, 22, 23]],
+
+           [[24, 25, 26, 27],
+            [28, 29, 30, 31],
+            [32, 33, 34, 35]]])
+    >>> block_reduce(image, block_size=(3, 3, 1), func=np.mean)
+    array([[[ 16.,  17.,  18.,  19.]]])
+    >>> block_reduce(image, block_size=(1, 3, 4), func=np.max)
+    array([[[11]],
+
+           [[23]],
+
+           [[35]]])
+    >>> block_reduce(image, block_size=(3, 1, 4), func=np.max)
+    array([[[27],
+            [31],
+            [35]]])
     """
 
     if len(block_size) != image.ndim: