undeprecate to_grayscale (#7707)

test/test_transforms_v2_functional.py

@@ -539,6 +539,7 @@ class TestDispatchers:
             (F.to_pil_image, F.to_image_pil),
             (F.elastic_transform, F.elastic),
             (F.convert_image_dtype, F.convert_dtype_image_tensor),
+            (F.to_grayscale, F.rgb_to_grayscale),
         ]
     ],
 )

torchvision/transforms/functional.py

@@ -1248,7 +1248,7 @@ def affine(
 
 # Looks like to_grayscale() is a stand-alone functional that is never called
 # from the transform classes. Perhaps it's still here for BC? I can't be
-# bothered to dig. Anyway, this can be deprecated as we migrate to V2.
+# bothered to dig.
 @torch.jit.unused
 def to_grayscale(img, num_output_channels=1):
     """Convert PIL image of any mode (RGB, HSV, LAB, etc) to grayscale version of image.

torchvision/transforms/v2/functional/__init__.py

@@ -76,6 +76,7 @@ from ._color import (
     solarize_image_pil,
     solarize_image_tensor,
     solarize_video,
+    to_grayscale,
 )
 from ._geometry import (
     affine,
@@ -168,4 +169,4 @@ from ._misc import (
 from ._temporal import uniform_temporal_subsample, uniform_temporal_subsample_video
 from ._type_conversion import pil_to_tensor, to_image_pil, to_image_tensor, to_pil_image
 
-from ._deprecated import get_image_size, to_grayscale, to_tensor  # usort: skip
+from ._deprecated import get_image_size, to_tensor  # usort: skip

torchvision/transforms/v2/functional/_color.py

@@ -56,6 +56,11 @@ def rgb_to_grayscale(
         )
 
 
+# `to_grayscale` actually predates `rgb_to_grayscale` in v1, but only handles PIL images. Since `rgb_to_grayscale` is a
+# superset in terms of functionality and has the same signature, we alias here to avoid disruption.
+to_grayscale = rgb_to_grayscale
+
+
 def _blend(image1: torch.Tensor, image2: torch.Tensor, ratio: float) -> torch.Tensor:
     ratio = float(ratio)
     fp = image1.is_floating_point()

torchvision/transforms/v2/functional/_deprecated.py

 import warnings
 from typing import Any, List, Union
 
-import PIL.Image
 import torch
 
 from torchvision import datapoints
 from torchvision.transforms import functional as _F
 
 
-@torch.jit.unused
-def to_grayscale(inpt: PIL.Image.Image, num_output_channels: int = 1) -> PIL.Image.Image:
-    warnings.warn(
-        "The function `to_grayscale` is deprecated in will be removed in a future release. "
-        "Instead, please use `rgb_to_grayscale`.",
-    )
-    return _F.to_grayscale(inpt, num_output_channels=num_output_channels)
-
-
 @torch.jit.unused
 def to_tensor(inpt: Any) -> torch.Tensor:
     warnings.warn(