Scaling 16-bit Greyscale PNGs

[Xaldew]

Environment

Python Version: Python 3.10.12

Nikola Version: Nikola v8.3.1

Operating System: Ubuntu 22.04 (Jammy)

Description:

It seems like it's not possible to create thumbnails for PNG files that are using the 16-bit greyscale format (sample file attached below). I'm currently seeing the warning:

[2025-04-27 14:34:47] WARNING: scale_images: Can't process images/teaser.png, using original image! (image has wrong mode)
[2025-04-27 14:34:47] WARNING: scale_images: Can't process images/teaser.png, using original image! (image has wrong mode)

I had a brief look at the image_processing.py file (https://github.com/getnikola/nikola/blob/master/nikola/image_processing.py#L153), and it seems like most of the work is delegated to Pillow, which, as far as I can tell, should support greyscale 16-bit images through the I;16 format (https://pillow.readthedocs.io/en/stable/handbook/concepts.html), as such it's unclear what the real issue is here.

Tangentially, it may also be a good thing to include what the mode is in the error message above.