[fbsync] Replace getbands() with get_image_num_channels() (#6941)

Reviewed By: NicolasHug

Differential Revision: D41265203

fbshipit-source-id: 082a28ef8f8809e313c2ecf014ea156c943adb92

Author: Yosua Michael Maranatha

torchvision/transforms/functional.py

@@ -167,7 +167,7 @@ def to_tensor(pic) -> Tensor:
 
     if pic.mode == "1":
         img = 255 * img
-    img = img.view(pic.size[1], pic.size[0], len(pic.getbands()))
+    img = img.view(pic.size[1], pic.size[0], F_pil.get_image_num_channels(pic))
     # put it from HWC to CHW format
     img = img.permute((2, 0, 1)).contiguous()
     if isinstance(img, torch.ByteTensor):
@@ -205,7 +205,7 @@ def pil_to_tensor(pic: Any) -> Tensor:
 
     # handle PIL Image
     img = torch.as_tensor(np.array(pic, copy=True))
-    img = img.view(pic.size[1], pic.size[0], len(pic.getbands()))
+    img = img.view(pic.size[1], pic.size[0], F_pil.get_image_num_channels(pic))
     # put it from HWC to CHW format
     img = img.permute((2, 0, 1))
     return img