Support grayscale images in numpy_to_pil (huggingface#1025)

Author: anton-l

src/diffusers/pipeline_flax_utils.py

@@ -444,7 +444,11 @@ def numpy_to_pil(images):
         if images.ndim == 3:
             images = images[None, ...]
         images = (images * 255).round().astype("uint8")
-        pil_images = [Image.fromarray(image) for image in images]
+        if images.shape[-1] == 1:
+            # special case for grayscale (single channel) images
+            pil_images = [Image.fromarray(image.squeeze(), mode="L") for image in images]
+        else:
+            pil_images = [Image.fromarray(image) for image in images]
 
         return pil_images
 

src/diffusers/pipeline_utils.py

@@ -625,7 +625,11 @@ def numpy_to_pil(images):
         if images.ndim == 3:
             images = images[None, ...]
         images = (images * 255).round().astype("uint8")
-        pil_images = [Image.fromarray(image) for image in images]
+        if images.shape[-1] == 1:
+            # special case for grayscale (single channel) images
+            pil_images = [Image.fromarray(image.squeeze(), mode="L") for image in images]
+        else:
+            pil_images = [Image.fromarray(image) for image in images]
 
         return pil_images