Assert that image reads succeed

Reviewed By: rbgirshick

Differential Revision: D6871605

fbshipit-source-id: 284a9267645cb039c2b20b8ceab68309664b0133

lib/datasets/json_dataset.py

@@ -134,9 +134,11 @@ class JsonDataset(object):
         # Reference back to the parent dataset
         entry['dataset'] = self
         # Make file_name an abs path
-        entry['image'] = os.path.join(
+        im_path = os.path.join(
             self.image_directory, self.image_prefix + entry['file_name']
         )
+        assert os.path.exists(im_path), 'Image \'{}\' not found'.format(im_path)
+        entry['image'] = im_path
         entry['flipped'] = False
         entry['has_visible_keypoints'] = False
         # Empty placeholders

lib/roi_data/minibatch.py

@@ -99,6 +99,8 @@ def _get_image_blob(roidb):
     im_scales = []
     for i in range(num_images):
         im = cv2.imread(roidb[i]['image'])
+        assert im is not None, \
+            'Failed to read image \'{}\''.format(roidb[i]['image'])
         if roidb[i]['flipped']:
             im = im[:, ::-1, :]
         target_size = cfg.TRAIN.SCALES[scale_inds[i]]