add PermuteChannels transform

docs/source/transforms.rst

@@ -155,6 +155,7 @@ Color
 
     ColorJitter
     v2.ColorJitter
+    v2.RandomChannelPermutation
     v2.RandomPhotometricDistort
     Grayscale
     v2.Grayscale

test/test_transforms_v2.py

@@ -124,6 +124,7 @@ class TestSmoke:
             (transforms.RandomEqualize(p=1.0), None),
             (transforms.RandomGrayscale(p=1.0), None),
             (transforms.RandomInvert(p=1.0), None),
+            (transforms.RandomChannelPermutation(), None),
             (transforms.RandomPhotometricDistort(p=1.0), None),
             (transforms.RandomPosterize(bits=4, p=1.0), None),
             (transforms.RandomSolarize(threshold=0.5, p=1.0), None),

test/test_transforms_v2_refactored.py

@@ -2280,3 +2280,61 @@ def resize_my_datapoint():
         _register_kernel_internal(F.resize, MyDatapoint, datapoint_wrapper=False)(resize_my_datapoint)
 
         assert _get_kernel(F.resize, MyDatapoint) is resize_my_datapoint
+
+
+class TestPermuteChannels:
+    _DEFAULT_PERMUTATION = [2, 0, 1]
+
+    @pytest.mark.parametrize(
+        ("kernel", "make_input"),
+        [
+            (F.permute_channels_image_tensor, make_image_tensor),
+            # FIXME
+            # check_kernel does not support PIL kernel, but it should
+            (F.permute_channels_image_tensor, make_image),
+            (F.permute_channels_video, make_video),
+        ],
+    )
+    @pytest.mark.parametrize("dtype", [torch.float32, torch.uint8])
+    @pytest.mark.parametrize("device", cpu_and_cuda())
+    def test_kernel(self, kernel, make_input, dtype, device):
+        check_kernel(kernel, make_input(dtype=dtype, device=device), permutation=self._DEFAULT_PERMUTATION)
+
+    @pytest.mark.parametrize(
+        ("kernel", "make_input"),
+        [
+            (F.permute_channels_image_tensor, make_image_tensor),
+            (F.permute_channels_image_pil, make_image_pil),
+            (F.permute_channels_image_tensor, make_image),
+            (F.permute_channels_video, make_video),
+        ],
+    )
+    def test_dispatcher(self, kernel, make_input):
+        check_dispatcher(F.permute_channels, kernel, make_input(), permutation=self._DEFAULT_PERMUTATION)
+
+    @pytest.mark.parametrize(
+        ("kernel", "input_type"),
+        [
+            (F.permute_channels_image_tensor, torch.Tensor),
+            (F.permute_channels_image_pil, PIL.Image.Image),
+            (F.permute_channels_image_tensor, datapoints.Image),
+            (F.permute_channels_video, datapoints.Video),
+        ],
+    )
+    def test_dispatcher_signature(self, kernel, input_type):
+        check_dispatcher_kernel_signature_match(F.permute_channels, kernel=kernel, input_type=input_type)
+
+    def reference_image_correctness(self, image, permutation):
+        channel_images = image.split(1, dim=-3)
+        permuted_channel_images = [channel_images[channel_idx] for channel_idx in permutation]
+        return datapoints.Image(torch.concat(permuted_channel_images, dim=-3))
+
+    @pytest.mark.parametrize("permutation", [[2, 0, 1], [1, 2, 0], [2, 0, 1], [0, 1, 2]])
+    @pytest.mark.parametrize("batch_dims", [(), (2,), (2, 1)])
+    def test_image_correctness(self, permutation, batch_dims):
+        image = make_image(batch_dims=batch_dims)
+
+        actual = F.permute_channels(image, permutation=permutation)
+        expected = self.reference_image_correctness(image, permutation=permutation)
+
+        torch.testing.assert_close(actual, expected)

torchvision/transforms/v2/__init__.py

@@ -11,6 +11,7 @@
     Grayscale,
     RandomAdjustSharpness,
     RandomAutocontrast,
+    RandomChannelPermutation,
     RandomEqualize,
     RandomGrayscale,
     RandomInvert,

torchvision/transforms/v2/_color.py

@@ -177,7 +177,27 @@ def _transform(self, inpt: Any, params: Dict[str, Any]) -> Any:
         return output
 
 
-# TODO: This class seems to be untested
+class RandomChannelPermutation(Transform):
+    """[BETA] Randomly permute the channels of an image or video
+
+    .. v2betastatus:: RandomChannelPermutation transform
+    """
+
+    _transformed_types = (
+        datapoints.Image,
+        PIL.Image.Image,
+        is_simple_tensor,
+        datapoints.Video,
+    )
+
+    def _get_params(self, flat_inputs: List[Any]) -> Dict[str, Any]:
+        num_channels, *_ = query_chw(flat_inputs)
+        return dict(permutation=torch.randperm(num_channels))
+
+    def _transform(self, inpt: Any, params: Dict[str, Any]) -> Any:
+        return F.permute_channels(inpt, params["permutation"])
+
+
 class RandomPhotometricDistort(Transform):
     """[BETA] Randomly distorts the image or video as used in `SSD: Single Shot
     MultiBox Detector <https://arxiv.org/abs/1512.02325>`_.
@@ -241,21 +261,6 @@ def _get_params(self, flat_inputs: List[Any]) -> Dict[str, Any]:
         params["channel_permutation"] = torch.randperm(num_channels) if torch.rand(1) < self.p else None
         return params
 
-    def _permute_channels(
-        self, inpt: Union[datapoints._ImageType, datapoints._VideoType], permutation: torch.Tensor
-    ) -> Union[datapoints._ImageType, datapoints._VideoType]:
-        orig_inpt = inpt
-        if isinstance(orig_inpt, PIL.Image.Image):
-            inpt = F.pil_to_tensor(inpt)
-
-        # TODO: Find a better fix than as_subclass???
-        output = inpt[..., permutation, :, :].as_subclass(type(inpt))
-
-        if isinstance(orig_inpt, PIL.Image.Image):
-            output = F.to_image_pil(output)
-
-        return output
-
     def _transform(
         self, inpt: Union[datapoints._ImageType, datapoints._VideoType], params: Dict[str, Any]
     ) -> Union[datapoints._ImageType, datapoints._VideoType]:
@@ -270,7 +275,7 @@ def _transform(
         if params["contrast_factor"] is not None and not params["contrast_before"]:
             inpt = F.adjust_contrast(inpt, contrast_factor=params["contrast_factor"])
         if params["channel_permutation"] is not None:
-            inpt = self._permute_channels(inpt, permutation=params["channel_permutation"])
+            inpt = F.permute_channels(inpt, permutation=params["channel_permutation"])
         return inpt
 
 

torchvision/transforms/v2/functional/__init__.py

@@ -62,6 +62,10 @@
     invert_image_pil,
     invert_image_tensor,
     invert_video,
+    permute_channels,
+    permute_channels_image_pil,
+    permute_channels_image_tensor,
+    permute_channels_video,
     posterize,
     posterize_image_pil,
     posterize_image_tensor,

torchvision/transforms/v2/functional/_color.py

@@ -1,4 +1,4 @@
-from typing import Union
+from typing import List, Union
 
 import PIL.Image
 import torch
@@ -10,6 +10,8 @@
 from torchvision.utils import _log_api_usage_once
 
 from ._misc import _num_value_bits, to_dtype_image_tensor
+
+from ._type_conversion import pil_to_tensor, to_image_pil
 from ._utils import _get_kernel, _register_explicit_noop, _register_kernel_internal
 
 
@@ -641,3 +643,64 @@ def invert_image_tensor(image: torch.Tensor) -> torch.Tensor:
 @_register_kernel_internal(invert, datapoints.Video)
 def invert_video(video: torch.Tensor) -> torch.Tensor:
     return invert_image_tensor(video)
+
+
+@_register_explicit_noop(datapoints.BoundingBoxes, datapoints.Mask)
+def permute_channels(inpt: datapoints._InputTypeJIT, permutation: List[int]) -> datapoints._InputTypeJIT:
+    """Permute the channels of the input according to the given permutation.
+
+    This function supports plain :class:`~torch.Tensor`'s, :class:`PIL.Image.Image`'s, and
+    :class:`torchvision.datapoints.Image` and :class:`torchvision.datapoints.Video`.
+
+    Example:
+        >>> rgb_image = torch.rand(3, 256, 256)
+        >>> bgr_image = F.permutate_channels(rgb_image, permutation=[2, 1, 0])
+
+    Args:
+        permutation (List[int]): Valid permutation of the input channel indices. The index of the element determines the
+            channel index in the input and the value determines the channel index in the output. For example,
+            ``permutation=[2, 0 , 1]``
+
+            - takes ``ìnpt[..., 0, :, :]`` and puts it at ``output[..., 2, :, :]``,
+            - takes ``ìnpt[..., 1, :, :]`` and puts it at ``output[..., 0, :, :]``, and
+            - takes ``ìnpt[..., 2, :, :]`` and puts it at ``output[..., 1, :, :]``.
+
+    Raises:
+        ValueError: If ``len(permutation)`` doesn't match the number of channels in the input.
+    """
+    if torch.jit.is_scripting():
+        return permute_channels_image_tensor(inpt, permutation=permutation)
+
+    _log_api_usage_once(permute_channels)
+
+    kernel = _get_kernel(permute_channels, type(inpt))
+    return kernel(inpt, permutation=permutation)
+
+
+@_register_kernel_internal(permute_channels, torch.Tensor)
+@_register_kernel_internal(permute_channels, datapoints.Image)
+def permute_channels_image_tensor(image: torch.Tensor, permutation: List[int]) -> torch.Tensor:
+    shape = image.shape
+    num_channels, height, width = shape[-3:]
+
+    if len(permutation) != num_channels:
+        raise ValueError(
+            f"Length of permutation does not match number of channels: " f"{len(permutation)} != {num_channels}"
+        )
+
+    if image.numel() == 0:
+        return image
+
+    image = image.reshape(-1, num_channels, height, width)
+    image = image[:, permutation, :, :]
+    return image.reshape(shape)
+
+
+@_register_kernel_internal(permute_channels, PIL.Image.Image)
+def permute_channels_image_pil(image: PIL.Image.Image, permutation: List[int]) -> PIL.Image:
+    return to_image_pil(permute_channels_image_tensor(pil_to_tensor(image), permutation=permutation))
+
+
+@_register_kernel_internal(permute_channels, datapoints.Video)
+def permute_channels_video(video: torch.Tensor, permutation: List[int]) -> torch.Tensor:
+    return permute_channels_image_tensor(video, permutation=permutation)