Throw warning for empty masks or box tensors on draw_segmentation_masks and...

Throw warning for empty masks or box tensors on draw_segmentation_masks and draw_bounding_boxes (#5857)

* Fixing the IndexError in draw_segmentation_masks

* fixing the bug on draw_bounding_boxes

* Changing fstring to normal string

* Removing unecessary conversion

* Adding test for the change

* Adding a test for draw seqmentation mask

* Fixing small mistake

* Fixing an error in the tests

* removing useless imports

* ufmt
Co-authored-by: LEGRAND Matthieu <legrand.ma@chu-toulouse.fr>
Co-authored-by: Nicolas Hug <contact@nicolas-hug.com>

test/test_utils.py

@@ -176,6 +176,15 @@ def test_draw_boxes_warning():
         utils.draw_bounding_boxes(img, boxes, font_size=11)
 
 
+def test_draw_no_boxes():
+    img = torch.full((3, 100, 100), 0, dtype=torch.uint8)
+    boxes = torch.full((0, 4), 0, dtype=torch.float)
+    with pytest.warns(UserWarning, match=re.escape("boxes doesn't contain any box. No box was drawn")):
+        res = utils.draw_bounding_boxes(img, boxes)
+        # Check that the function didnt change the image
+        assert res.eq(img).all()
+
+
 @pytest.mark.parametrize(
     "colors",
     [
@@ -266,6 +275,15 @@ def test_draw_segmentation_masks_errors():
         utils.draw_segmentation_masks(image=img, masks=masks, colors=bad_colors)
 
 
+def test_draw_no_segmention_mask():
+    img = torch.full((3, 100, 100), 0, dtype=torch.uint8)
+    masks = torch.full((0, 100, 100), 0, dtype=torch.bool)
+    with pytest.warns(UserWarning, match=re.escape("masks doesn't contain any mask. No mask was drawn")):
+        res = utils.draw_segmentation_masks(img, masks)
+        # Check that the function didnt change the image
+        assert res.eq(img).all()
+
+
 def test_draw_keypoints_vanilla():
     # Keypoints is declared on top as global variable
     keypoints_cp = keypoints.clone()

torchvision/utils.py

@@ -211,6 +211,10 @@ def draw_bounding_boxes(
 
     num_boxes = boxes.shape[0]
 
+    if num_boxes == 0:
+        warnings.warn("boxes doesn't contain any box. No box was drawn")
+        return image
+
     if labels is None:
         labels: Union[List[str], List[None]] = [None] * num_boxes  # type: ignore[no-redef]
     elif len(labels) != num_boxes:
@@ -311,6 +315,10 @@ def draw_segmentation_masks(
     if colors is not None and num_masks > len(colors):
         raise ValueError(f"There are more masks ({num_masks}) than colors ({len(colors)})")
 
+    if num_masks == 0:
+        warnings.warn("masks doesn't contain any mask. No mask was drawn")
+        return image
+
     if colors is None:
         colors = _generate_color_palette(num_masks)