Fix alpha_mask transformation

Author: u-haru

library/train_util.py

@@ -1169,7 +1169,7 @@ def __getitem__(self, index):
                 alpha_mask = cv2.resize(
                     alpha_mask, target_size, interpolation=cv2.INTER_AREA
                 )
-                alpha_mask = self.image_transforms(alpha_mask)
+                alpha_mask = transforms.ToTensor()(alpha_mask)
                 alpha_mask_list.append(alpha_mask)
 
             if not flipped:
@@ -2338,6 +2338,7 @@ def cache_batch_latents(
                 image = image[:, :, :3]
             else:
                 alpha_mask = np.full_like(image[:, :, 0], 255, dtype=np.uint8) # [W,H]
+            alpha_mask = transforms.ToTensor()(alpha_mask)
             alpha_masks.append(alpha_mask)
         else:
             alpha_masks.append(None)