quite a bump on this subject, the webp compression borks the black level, artifacting pictures, but there is no real solution for this, others algos wont do better.
an example with a difficult picture to compress, the black is at the very limit, even downsizing gives crushed blacks. It's original size is fine however, so watch it in fullscreen by clicking the link
https://i.ibb.co/wLrh3ZG/2k-Skyrim-SE-2023-07-21-16-12-21-upscayl-4x-remacri.png -png
https://staticdelivery.nexusmods.com/images/1704/1798547-1717309647.png - Webp
some artifacts.
Jpg max compression 4:2:0 84% quality has better shadow details, for the same size ! because it compresses the shadows progressively, reducing the perceivable black aureolas. Technically degrading the picture more, perceptually it is more correct. (but the rest of the picture is degraded much more than webp)
https://i.ibb.co/CtHFrfZ/2k-Skyrim-SE-2023-07-21-16-12-21-upscayl-4x-remacri.jpg -jpg 4:2:0 84% quality same size than webp, 290kb
Avif is slightly better but it has a server cost to compress for acceptable result, it's clearly less efficient.
JPEG XR preserves the black better without very annoying (still there, less perceivable) artifacts but at slightly higher size, 380 kb, at a specific compression ratio, too much and it breaks black, too high and it artifacts even more. Also, it cannot be read by some browsers.
After testing, webp is a logical choice for compression.
HOWEVER, we could have an option for a webp lossless hosting and browsing (nexus would always provide lossless pics when available, if someone hosted a lossless pic), at a price on top of the actual premium service. Like lossless audio on streaming platforms. If i remember correctly, many years ago, (2015-2017?) the pictures werent compressed that much and looked better. But it's maybe my memory.
I know, there is many 3rd party websites to host lossless pics, but it's a pain in the ass, to say the least. It would be comfortable to handle lossless pics on nexus and it could be another way to support this amazing modding platform.
2kSkyrimSE 2023-07-21 16-12-21_upscayl_4x_remacri.jxr
