Yeah, it’s not that we specifically removed support… it’s that we do a lot more image processing and optimization than we used to and it’s a consequence of that.
I did some testing on a local instance, and I think the key for HDR images in Discourse right now is to use an AVIF format with a gain map, which will avoid optimization without any site setting changes.
One catch is that we do not keep the gain map when resizing, so if your site has the Create thumbnails site setting enabled… then you only see the HDR version of the image when you click the thumbnail to view the lightboxed image. You could disable that setting, but it means everyone visiting your site is always downloading the full sized image… which can be quite a lot on slow or metered connections, but maybe this is an acceptable tradeoff on a photography site.
Here’s an example AVIF image from Eric Chan that should work in HDR on Meta when opened in the lightbox. You can probably see some color shifts going from thumbnail → lightbox.
