Fix: color_splash when no masks are detected

Reported here: https://github.com/matterport/Mask_RCNN/pull/500

mrcnn/model.py

@@ -2429,7 +2429,7 @@ class MaskRCNN():
             full_mask = utils.unmold_mask(masks[i], boxes[i], original_image_shape)
             full_masks.append(full_mask)
         full_masks = np.stack(full_masks, axis=-1)\
-            if full_masks else np.empty(masks.shape[1:3] + (0,))
+            if full_masks else np.empty(original_image_shape[:2] + (0,))
 
         return boxes, class_ids, scores, full_masks
 

samples/balloon/balloon.py

@@ -204,13 +204,13 @@ def color_splash(image, mask):
     # Make a grayscale copy of the image. The grayscale copy still
     # has 3 RGB channels, though.
     gray = skimage.color.gray2rgb(skimage.color.rgb2gray(image)) * 255
-    # We're treating all instances as one, so collapse the mask into one layer
-    mask = (np.sum(mask, -1, keepdims=True) >= 1)
     # Copy color pixels from the original color image where mask is set
-    if mask.shape[0] > 0:
+    if mask.shape[-1] > 0:
+        # We're treating all instances as one, so collapse the mask into one layer
+        mask = (np.sum(mask, -1, keepdims=True) >= 1)
         splash = np.where(mask, image, gray).astype(np.uint8)
     else:
-        splash = gray
+        splash = gray.astype(np.uint8)
     return splash