Restore _split_alpha.

Author: datumbox

torchvision/prototype/transforms/functional/_meta.py

@@ -183,8 +183,12 @@ def clamp_bounding_box(
     return convert_format_bounding_box(xyxy_boxes, BoundingBoxFormat.XYXY, format)
 
 
+def _split_alpha(image: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
+    return torch.tensor_split(image, indices=(-1,), dim=-3)
+
+
 def _strip_alpha(image: torch.Tensor) -> torch.Tensor:
-    image, alpha = torch.tensor_split(image, indices=(-1,), dim=-3)
+    image, alpha = _split_alpha(image)
     if not torch.all(alpha == _FT._max_value(alpha.dtype)):
         raise RuntimeError(
             "Stripping the alpha channel if it contains values other than the max value is not supported."
@@ -233,7 +237,7 @@ def convert_color_space_image_tensor(
     elif old_color_space == ColorSpace.GRAY_ALPHA and new_color_space == ColorSpace.RGB:
         return _gray_to_rgb(_strip_alpha(image))
     elif old_color_space == ColorSpace.GRAY_ALPHA and new_color_space == ColorSpace.RGB_ALPHA:
-        image, alpha = torch.tensor_split(image, indices=(-1,), dim=-3)
+        image, alpha = _split_alpha(image)
         return _add_alpha(_gray_to_rgb(image), alpha)
     elif old_color_space == ColorSpace.RGB and new_color_space == ColorSpace.GRAY:
         return _rgb_to_gray(image)
@@ -244,7 +248,7 @@ def convert_color_space_image_tensor(
     elif old_color_space == ColorSpace.RGB_ALPHA and new_color_space == ColorSpace.GRAY:
         return _rgb_to_gray(_strip_alpha(image))
     elif old_color_space == ColorSpace.RGB_ALPHA and new_color_space == ColorSpace.GRAY_ALPHA:
-        image, alpha = torch.tensor_split(image, indices=(-1,), dim=-3)
+        image, alpha = _split_alpha(image)
         return _add_alpha(_rgb_to_gray(image), alpha)
     elif old_color_space == ColorSpace.RGB_ALPHA and new_color_space == ColorSpace.RGB:
         return _strip_alpha(image)