fixed resize_image for the case of constant images

python/caffe/io.py

@@ -43,11 +43,17 @@ def resize_image(im, new_dims, interp_order=1):
     im: resized ndarray with shape (new_dims[0], new_dims[1], K)
     """
     if im.shape[-1] == 1 or im.shape[-1] == 3:
-        # skimage is fast but only understands {1,3} channel images in [0, 1].
         im_min, im_max = im.min(), im.max()
-        im_std = (im - im_min) / (im_max - im_min)
-        resized_std = resize(im_std, new_dims, order=interp_order)
-        resized_im = resized_std * (im_max - im_min) + im_min
+        if im_max > im_min:
+            # skimage is fast but only understands {1,3} channel images in [0, 1].
+            im_std = (im - im_min) / (im_max - im_min)
+            resized_std = resize(im_std, new_dims, order=interp_order)
+            resized_im = resized_std * (im_max - im_min) + im_min
+        else:
+            # the image is a constant -- avoid divide by 0
+            ret = np.empty((new_dims[0], new_dims[1], im.shape[-1]), dtype=np.float32)
+            ret.fill(im_min)
+            return ret
     else:
         # ndimage interpolates anything but more slowly.
         scale = tuple(np.array(new_dims) / np.array(im.shape[:2]))