Photo colors badly altered

[Ted]

I’m in the middle of publishing photos from a recent family wedding. While nextcloud is doing a fine job allowing us to sync the photos from user to user, something is going horribly wrong with the way the look in the web interface. Colors are drained and altered in a way that has our photographer pulling her hair out. Here’s an example:

The left image is what I see when I open the file (synced via nextcloud) on my hard drive. The right image is what I see if I pull up that same file in nextcloud. Note how grey the skin tones are. I’m running the latest version of the photos app, although it doesn’t appear to be generating properly. Is there a setting somewhere I can adjust?

Clearly, the system is generating some sort of preview for the web, but it’s losing a lot of color information in the process.

Thanks for any help you can provide!

Nextcloud version: 19.0.1
Operating system and version: Nethserver 7.8.2003
Apache or nginx version: Apache/2.4.6 (CentOS)
PHP version: 7.3

[Ted]

After a day of extensive investigation and some trial and error, I can describe the problem in greater detail.

Our photographer used the ‘ProPhoto RGB’ color profile for all of her photos. When she converts to the ‘sRGB’ profile the generated previews look correct. However, this conversion does cause some loss.

If I understand correctly, previews are being generated by GD. Something is going wrong in the conversion because GD isn’t properly reading the color profile.

Is it possible for me to manually generate previews with ImageMagik or some other tool and replace the preview cache?