[Cherry-pick for 0.17.1] Fix convert_bounding_box_format when passing strings (#8267)

Author: NicolasHug

test/test_transforms_v2.py

@@ -3397,6 +3397,23 @@ def test_transform(self, old_format, new_format, format_type):
             make_bounding_boxes(format=old_format),
         )
 
+    @pytest.mark.parametrize(("old_format", "new_format"), old_new_formats)
+    def test_strings(self, old_format, new_format):
+        # Non-regression test for https://github.com/pytorch/vision/issues/8258
+        input = tv_tensors.BoundingBoxes(torch.tensor([[10, 10, 20, 20]]), format=old_format, canvas_size=(50, 50))
+        expected = self._reference_convert_bounding_box_format(input, new_format)
+
+        old_format = old_format.name
+        new_format = new_format.name
+
+        out_functional = F.convert_bounding_box_format(input, new_format=new_format)
+        out_functional_tensor = F.convert_bounding_box_format(
+            input.as_subclass(torch.Tensor), old_format=old_format, new_format=new_format
+        )
+        out_transform = transforms.ConvertBoundingBoxFormat(new_format)(input)
+        for out in (out_functional, out_functional_tensor, out_transform):
+            assert_equal(out, expected)
+
     def _reference_convert_bounding_box_format(self, bounding_boxes, new_format):
         return tv_tensors.wrap(
             torchvision.ops.box_convert(

torchvision/transforms/v2/_meta.py

@@ -17,12 +17,10 @@ class ConvertBoundingBoxFormat(Transform):
 
     def __init__(self, format: Union[str, tv_tensors.BoundingBoxFormat]) -> None:
         super().__init__()
-        if isinstance(format, str):
-            format = tv_tensors.BoundingBoxFormat[format]
         self.format = format
 
     def _transform(self, inpt: tv_tensors.BoundingBoxes, params: Dict[str, Any]) -> tv_tensors.BoundingBoxes:
-        return F.convert_bounding_box_format(inpt, new_format=self.format)  # type: ignore[return-value]
+        return F.convert_bounding_box_format(inpt, new_format=self.format)  # type: ignore[return-value, arg-type]
 
 
 class ClampBoundingBoxes(Transform):

torchvision/transforms/v2/functional/_meta.py

@@ -214,6 +214,11 @@ def convert_bounding_box_format(
     if not torch.jit.is_scripting():
         _log_api_usage_once(convert_bounding_box_format)
 
+    if isinstance(old_format, str):
+        old_format = BoundingBoxFormat[old_format.upper()]
+    if isinstance(new_format, str):
+        new_format = BoundingBoxFormat[new_format.upper()]
+
     if torch.jit.is_scripting() or is_pure_tensor(inpt):
         if old_format is None:
             raise ValueError("For pure tensor inputs, `old_format` has to be passed.")