fix to_grayscale deprecation warning

[pmeier]

Fixes #7700. In #7120 we removed F.convert_colorspace and undeprecated F.rgb_to_grayscale in #7122. We just forgot to adapt the deprecation warning.

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This comment was automatically generated by Dr. CI and updates every 15 minutes.

[NicolasHug]

I forgot but... Did we decide to still deprecate to_grayscale? (I remember it was a bit messy...)

[pmeier]

Did we decide to still deprecate to_grayscale? (I remember it was a bit messy...)

It is. In v1 we have both

• vision/torchvision/transforms/functional.py

  Lines 1249 to 1253 in d814772

  	# 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.
  	@torch.jit.unused
  	def to_grayscale(img, num_output_channels=1):

• vision/torchvision/transforms/functional.py

  Line 1275 in d814772

  def rgb_to_grayscale(img: Tensor, num_output_channels: int = 1) -> Tensor:

For some reason, to_grayscale only handles PIL images:

vision/torchvision/transforms/functional.py

Lines 1269 to 1272 in d814772

	if isinstance(img, Image.Image):
	return F_pil.to_grayscale(img, num_output_channels)
	raise TypeError("Input should be PIL Image")

rgb_to_grayscale handles both PIL and tensor images and dispatches to to_grayscale for the former:

vision/torchvision/transforms/functional.py

Lines 1296 to 1299 in d814772

	if not isinstance(img, torch.Tensor):
	return F_pil.to_grayscale(img, num_output_channels)
	return F_t.rgb_to_grayscale(img, num_output_channels)

Meaning, in the (now private) _functional_tensor there is no to_grayscale and in _functional_pil there is no rgb_to_grayscale.

The transforms ToGrayscale and RandomGrayscale in v1 and v2 only use rgb_to_grayscale, which is why we deprecated to_grayscale in v2.

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