[Feature Request] PadToSquare: Square Padding to Preserve Aspect Ratios When Resizing Images with Varied Shapes in torchvision.transforms.v2

docs/source/transforms.rst

@@ -316,6 +316,7 @@ Others
     v2.RandomHorizontalFlip
     v2.RandomVerticalFlip
     v2.Pad
+    v2.PadToSquare
     v2.RandomZoomOut
     v2.RandomRotation
     v2.RandomAffine

test/test_transforms_v2.py

@@ -3928,6 +3928,44 @@ def test_bounding_boxes_correctness(self, padding, format, dtype, device, fn):
         assert_equal(actual, expected)
 
 
+class TestPadToSquare:
+    @pytest.mark.parametrize(
+        "image",
+        [
+            (make_image((3, 10), device="cpu", dtype=torch.uint8)),
+            (make_image((10, 3), device="cpu", dtype=torch.uint8)),
+            (make_image((10, 10), device="cpu", dtype=torch.uint8)),
+        ],
+    )
+    def test__get_params(self, image):
+        transform = transforms.PadToSquare()
+        params = transform._get_params([image])
+
+        assert "padding" in params
+        padding = params["padding"]
+
+        assert len(padding) == 4
+        assert all(p >= 0 for p in padding)
+
+        height, width = F.get_size(image)
+        assert max(height, width) == height + padding[1] + padding[3]
+        assert max(height, width) == width + padding[0] + padding[2]
+
+    @pytest.mark.parametrize(
+        "image, expected_output_shape",
+        [
+            (make_image((3, 10), device="cpu", dtype=torch.uint8), [10, 10]),
+            (make_image((10, 3), device="cpu", dtype=torch.uint8), [10, 10]),
+            (make_image((10, 10), device="cpu", dtype=torch.uint8), [10, 10]),
+        ],
+    )
+    def test_pad_square_correctness(self, image, expected_output_shape):
+        transform = transforms.PadToSquare()
+        output = transform(image)
+
+        assert F.get_size(output) == expected_output_shape
+
+
 class TestCenterCrop:
     INPUT_SIZE = (17, 11)
     OUTPUT_SIZES = [(3, 5), (5, 3), (4, 4), (21, 9), (13, 15), (19, 14), 3, (4,), [5], INPUT_SIZE]

torchvision/transforms/v2/__init__.py

@@ -26,6 +26,7 @@
     ElasticTransform,
     FiveCrop,
     Pad,
+    PadToSquare,
     RandomAffine,
     RandomCrop,
     RandomHorizontalFlip,

torchvision/transforms/v2/_geometry.py

@@ -488,6 +488,84 @@ def _transform(self, inpt: Any, params: Dict[str, Any]) -> Any:
         return self._call_kernel(F.pad, inpt, padding=self.padding, fill=fill, padding_mode=self.padding_mode)  # type: ignore[arg-type]
 
 
+class PadToSquare(Transform):
+    """Pad a non-square input to make it square by padding the shorter side to match the longer side.
+
+    Args:
+        fill (number or tuple or dict, optional): Pixel fill value used when the  ``padding_mode`` is constant.
+            Default is 0. If a tuple of length 3, it is used to fill R, G, B channels respectively.
+            Fill value can be also a dictionary mapping data type to the fill value, e.g.
+            ``fill={tv_tensors.Image: 127, tv_tensors.Mask: 0}`` where ``Image`` will be filled with 127 and
+            ``Mask`` will be filled with 0.
+        padding_mode (str, optional): Type of padding. Should be: constant, edge, reflect or symmetric.
+            Default is "constant".
+
+            - constant: pads with a constant value, this value is specified with fill
+
+            - edge: pads with the last value at the edge of the image.
+
+            - reflect: pads with reflection of image without repeating the last value on the edge.
+              For example, padding [1, 2, 3, 4] with 2 elements on both sides in reflect mode
+              will result in [3, 2, 1, 2, 3, 4, 3, 2]
+
+            - symmetric: pads with reflection of image repeating the last value on the edge.
+              For example, padding [1, 2, 3, 4] with 2 elements on both sides in symmetric mode
+              will result in [2, 1, 1, 2, 3, 4, 4, 3]
+
+    Example:
+        >>> import torch
+        >>> from torchvision.transforms.v2 import PadToSquare
+        >>> rectangular_image = torch.randint(0, 255, (3, 224, 168), dtype=torch.uint8)
+        >>> transform = PadToSquare(padding_mode='constant', fill=0)
+        >>> square_image = transform(rectangular_image)
+        >>> print(square_image.size())
+        torch.Size([3, 224, 224])
+    """
+
+    def __init__(
+        self,
+        fill: Union[_FillType, Dict[Union[Type, str], _FillType]] = 0,
+        padding_mode: Literal["constant", "edge", "reflect", "symmetric"] = "constant",
+    ):
+        super().__init__()
+
+        _check_padding_mode_arg(padding_mode)
+
+        if padding_mode not in ["constant", "edge", "reflect", "symmetric"]:
+            raise ValueError("`padding_mode` must be one of 'constant', 'edge', 'reflect' or 'symmetric'.")
+        self.padding_mode = padding_mode
+        self.fill = _setup_fill_arg(fill)
+
+    def _get_params(self, flat_inputs: List[Any]) -> Dict[str, Any]:
+        # Get the original height and width from the inputs
+        orig_height, orig_width = query_size(flat_inputs)
+
+        # Find the target size (maximum of height and width)
+        target_size = max(orig_height, orig_width)
+
+        if orig_height < target_size:
+            # Need to pad height
+            pad_height = target_size - orig_height
+            pad_top = pad_height // 2
+            pad_bottom = pad_height - pad_top
+            pad_left = 0
+            pad_right = 0
+        else:
+            # Need to pad width
+            pad_width = target_size - orig_width
+            pad_left = pad_width // 2
+            pad_right = pad_width - pad_left
+            pad_top = 0
+            pad_bottom = 0
+
+        # The padding needs to be in the format [left, top, right, bottom]
+        return dict(padding=[pad_left, pad_top, pad_right, pad_bottom])
+
+    def _transform(self, inpt: Any, params: Dict[str, Any]) -> Any:
+        fill = _get_fill(self.fill, type(inpt))
+        return self._call_kernel(F.pad, inpt, padding=params["padding"], padding_mode=self.padding_mode, fill=fill)
+
+
 class RandomZoomOut(_RandomApplyTransform):
     """ "Zoom out" transformation from
     `"SSD: Single Shot MultiBox Detector" <https://arxiv.org/abs/1512.02325>`_.