Cannot write array of shape (H, W, 1) to JPEG image with v3 API

Switching from the v2 API to the v3 API, I noticed the following difference:

This works

import numpy as np
import imageio

x = np.zeros((10, 30, 1), dtype=np.uint8)
imageio.v2.imwrite("test.jpg", x)

while the same with imageio.v3.imwrite fails with the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\kpkx626\AppData\Local\Programs\Python\Python38\lib\site-packages\imageio\v3.py", line 161, in imwrite
    encoded = img_file.write(image, **kwargs)
  File "C:\Users\kpkx626\AppData\Local\Programs\Python\Python38\lib\site-packages\imageio\plugins\pillow.py", line 322, in write
    primary_image.save(self._request.get_file(), **save_args)
  File "C:\Users\kpkx626\AppData\Local\Programs\Python\Python38\lib\site-packages\PIL\Image.py", line 2305, in save
    save_handler = SAVE_ALL[format.upper()]
KeyError: 'JPEG'

This happens with Pillow 9.1.1 and 9.2.0 and Python 3.8.10 on Windows.

Is this considered an intended change, or should PillowPlugin.write squeeze out the third dimension?

[slanzmich]

@FirefoxMetzger I created #849 to address the tifffile plugin issue.

[FirefoxMetzger]

Another related thing I just noticed is that writing a TIFF image from an array of shape (256, 256, 3) writes multipage TIFF with 256 pages. (This uses the legacy tifffile plugin.)

@slanzmich Oh? This sounds quite right. Could you make a new issue for this? tifffile is an entirely different plugin so it uses a different code path than what I shared above.