Add min_area to `SanitizeBoundingBox` (#7735)

Co-authored-by: Nicolas Hug <contact@nicolas-hug.com>

test/test_transforms_v2.py

@@ -5805,7 +5805,7 @@ def test_detection_preset(image_type, data_augmentation, to_tensor, sanitize):
 
 
 class TestSanitizeBoundingBoxes:
-    def _get_boxes_and_valid_mask(self, H=256, W=128, min_size=10):
+    def _get_boxes_and_valid_mask(self, H=256, W=128, min_size=10, min_area=10):
         boxes_and_validity = [
             ([0, 1, 10, 1], False),  # Y1 == Y2
             ([0, 1, 0, 20], False),  # X1 == X2
@@ -5816,17 +5816,16 @@ class TestSanitizeBoundingBoxes:
             ([-1, 1, 10, 20], False),  # any < 0
             ([0, 0, -1, 20], False),  # any < 0
             ([0, 0, -10, -1], False),  # any < 0
-            ([0, 0, min_size, 10], True),  # H < min_size
-            ([0, 0, 10, min_size], True),  # W < min_size
-            ([0, 0, W, H], True),  # TODO: Is that actually OK?? Should it be -1?
-            ([1, 1, 30, 20], True),
-            ([0, 0, 10, 10], True),
-            ([1, 1, 30, 20], True),
+            ([0, 0, min_size, 10], min_size * 10 >= min_area),  # H < min_size
+            ([0, 0, 10, min_size], min_size * 10 >= min_area),  # W < min_size
+            ([0, 0, W, H], W * H >= min_area),
+            ([1, 1, 30, 20], 29 * 19 >= min_area),
+            ([0, 0, 10, 10], 9 * 9 >= min_area),
+            ([1, 1, 30, 20], 29 * 19 >= min_area),
         ]
 
         random.shuffle(boxes_and_validity)  # For test robustness: mix order of wrong and correct cases
         boxes, expected_valid_mask = zip(*boxes_and_validity)
-
         boxes = tv_tensors.BoundingBoxes(
             boxes,
             format=tv_tensors.BoundingBoxFormat.XYXY,
@@ -5835,7 +5834,7 @@ class TestSanitizeBoundingBoxes:
 
         return boxes, expected_valid_mask
 
-    @pytest.mark.parametrize("min_size", (1, 10))
+    @pytest.mark.parametrize("min_size, min_area", ((1, 1), (10, 1), (10, 101)))
     @pytest.mark.parametrize(
         "labels_getter",
         (
@@ -5848,7 +5847,7 @@ class TestSanitizeBoundingBoxes:
         ),
     )
     @pytest.mark.parametrize("sample_type", (tuple, dict))
-    def test_transform(self, min_size, labels_getter, sample_type):
+    def test_transform(self, min_size, min_area, labels_getter, sample_type):
 
         if sample_type is tuple and not isinstance(labels_getter, str):
             # The "lambda inputs: inputs["labels"]" labels_getter used in this test
@@ -5856,7 +5855,7 @@ class TestSanitizeBoundingBoxes:
             return
 
         H, W = 256, 128
-        boxes, expected_valid_mask = self._get_boxes_and_valid_mask(H=H, W=W, min_size=min_size)
+        boxes, expected_valid_mask = self._get_boxes_and_valid_mask(H=H, W=W, min_size=min_size, min_area=min_area)
         valid_indices = [i for (i, is_valid) in enumerate(expected_valid_mask) if is_valid]
 
         labels = torch.arange(boxes.shape[0])
@@ -5880,7 +5879,9 @@ class TestSanitizeBoundingBoxes:
             img = sample.pop("image")
             sample = (img, sample)
 
-        out = transforms.SanitizeBoundingBoxes(min_size=min_size, labels_getter=labels_getter)(sample)
+        out = transforms.SanitizeBoundingBoxes(min_size=min_size, min_area=min_area, labels_getter=labels_getter)(
+            sample
+        )
 
         if sample_type is tuple:
             out_image = out[0]
@@ -5977,6 +5978,8 @@ class TestSanitizeBoundingBoxes:
 
         with pytest.raises(ValueError, match="min_size must be >= 1"):
             transforms.SanitizeBoundingBoxes(min_size=0)
+        with pytest.raises(ValueError, match="min_area must be >= 1"):
+            transforms.SanitizeBoundingBoxes(min_area=0)
         with pytest.raises(ValueError, match="labels_getter should either be 'default'"):
             transforms.SanitizeBoundingBoxes(labels_getter=12)
 

torchvision/transforms/v2/_misc.py

@@ -344,7 +344,7 @@ class SanitizeBoundingBoxes(Transform):
 
     This transform removes bounding boxes and their associated labels/masks that:
 
-    - are below a given ``min_size``: by default this also removes degenerate boxes that have e.g. X2 <= X1.
+    - are below a given ``min_size`` or ``min_area``: by default this also removes degenerate boxes that have e.g. X2 <= X1.
     - have any coordinate outside of their corresponding image. You may want to
       call :class:`~torchvision.transforms.v2.ClampBoundingBoxes` first to avoid undesired removals.
 
@@ -359,7 +359,8 @@ class SanitizeBoundingBoxes(Transform):
     cases.
 
     Args:
-        min_size (float, optional) The size below which bounding boxes are removed. Default is 1.
+        min_size (float, optional): The size below which bounding boxes are removed. Default is 1.
+        min_area (float, optional): The area below which bounding boxes are removed. Default is 1.
         labels_getter (callable or str or None, optional): indicates how to identify the labels in the input
             (or anything else that needs to be sanitized along with the bounding boxes).
             By default, this will try to find a "labels" key in the input (case-insensitive), if
@@ -379,6 +380,7 @@ class SanitizeBoundingBoxes(Transform):
     def __init__(
         self,
         min_size: float = 1.0,
+        min_area: float = 1.0,
         labels_getter: Union[Callable[[Any], Any], str, None] = "default",
     ) -> None:
         super().__init__()
@@ -387,6 +389,10 @@ class SanitizeBoundingBoxes(Transform):
             raise ValueError(f"min_size must be >= 1, got {min_size}.")
         self.min_size = min_size
 
+        if min_area < 1:
+            raise ValueError(f"min_area must be >= 1, got {min_area}.")
+        self.min_area = min_area
+
         self.labels_getter = labels_getter
         self._labels_getter = _parse_labels_getter(labels_getter)
 
@@ -422,7 +428,9 @@ class SanitizeBoundingBoxes(Transform):
             format=boxes.format,
             canvas_size=boxes.canvas_size,
             min_size=self.min_size,
+            min_area=self.min_area,
         )
+
         params = dict(valid=valid, labels=labels)
         flat_outputs = [self._transform(inpt, params) for inpt in flat_inputs]
 

torchvision/transforms/v2/functional/_misc.py

@@ -322,12 +322,13 @@ def sanitize_bounding_boxes(
     format: Optional[tv_tensors.BoundingBoxFormat] = None,
     canvas_size: Optional[Tuple[int, int]] = None,
     min_size: float = 1.0,
+    min_area: float = 1.0,
 ) -> Tuple[torch.Tensor, torch.Tensor]:
     """Remove degenerate/invalid bounding boxes and return the corresponding indexing mask.
 
     This removes bounding boxes that:
 
-    - are below a given ``min_size``: by default this also removes degenerate boxes that have e.g. X2 <= X1.
+    - are below a given ``min_size`` or ``min_area``: by default this also removes degenerate boxes that have e.g. X2 <= X1.
     - have any coordinate outside of their corresponding image. You may want to
       call :func:`~torchvision.transforms.v2.functional.clamp_bounding_boxes` first to avoid undesired removals.
 
@@ -346,6 +347,7 @@ def sanitize_bounding_boxes(
             (size of the corresponding image/video).
             Must be left to none if ``bounding_boxes`` is a :class:`~torchvision.tv_tensors.BoundingBoxes` object.
         min_size (float, optional) The size below which bounding boxes are removed. Default is 1.
+        min_area (float, optional) The area below which bounding boxes are removed. Default is 1.
 
     Returns:
         out (tuple of Tensors): The subset of valid bounding boxes, and the corresponding indexing mask.
@@ -361,7 +363,7 @@ def sanitize_bounding_boxes(
         if isinstance(format, str):
             format = tv_tensors.BoundingBoxFormat[format.upper()]
         valid = _get_sanitize_bounding_boxes_mask(
-            bounding_boxes, format=format, canvas_size=canvas_size, min_size=min_size
+            bounding_boxes, format=format, canvas_size=canvas_size, min_size=min_size, min_area=min_area
         )
         bounding_boxes = bounding_boxes[valid]
     else:
@@ -374,7 +376,11 @@ def sanitize_bounding_boxes(
                 "Leave those to None or pass bounding_boxes as a pure tensor."
             )
         valid = _get_sanitize_bounding_boxes_mask(
-            bounding_boxes, format=bounding_boxes.format, canvas_size=bounding_boxes.canvas_size, min_size=min_size
+            bounding_boxes,
+            format=bounding_boxes.format,
+            canvas_size=bounding_boxes.canvas_size,
+            min_size=min_size,
+            min_area=min_area,
         )
         bounding_boxes = tv_tensors.wrap(bounding_boxes[valid], like=bounding_boxes)
 
@@ -386,6 +392,7 @@ def _get_sanitize_bounding_boxes_mask(
     format: tv_tensors.BoundingBoxFormat,
     canvas_size: Tuple[int, int],
     min_size: float = 1.0,
+    min_area: float = 1.0,
 ) -> torch.Tensor:
 
     bounding_boxes = _convert_bounding_box_format(
@@ -394,7 +401,7 @@ def _get_sanitize_bounding_boxes_mask(
 
     image_h, image_w = canvas_size
     ws, hs = bounding_boxes[:, 2] - bounding_boxes[:, 0], bounding_boxes[:, 3] - bounding_boxes[:, 1]
-    valid = (ws >= min_size) & (hs >= min_size) & (bounding_boxes >= 0).all(dim=-1)
+    valid = (ws >= min_size) & (hs >= min_size) & (bounding_boxes >= 0).all(dim=-1) & (ws * hs >= min_area)
     # TODO: Do we really need to check for out of bounds here? All
     # transforms should be clamping anyway, so this should never happen?
     image_h, image_w = canvas_size