> and was amazed that JPEG XL has more detail than AVIF at 0.05-0.1 bpp (~120KB 1080p)
bpp = bits per pixel, not bytes. At 1080p, "0.05-0.1 bpp" is 13-26 KB. Much smaller than what you were testing. Might want to recheck your sizes, if you are actually looking at 0.5 bpp it would not surprise me at all that you found JPEG XL superior.
At very small sizes like 0.1 bpp the results are debatable, but I think AVIF is a pretty clear winner if you aren't too bothered by blurring. Samples at 0.15 bpp:
I tried it out on my own site, and through trial-and-error I found that Chromium does in fact treat the "max-bpp" Document-Policy directives as bytes-per-pixel.
I could be wrong; my memory has faded. Please correct me if this is the case.
I'm not sure what HTTP headers have to do with anything. Using "bpp" to mean bits per pixel is extremely common in image encoding. See e.g. https://en.wikipedia.org/wiki/Color_depth where an uncompressed image is often 24 bpp (8 bits per channel). It's also common to use bitrate (rather than byterate) in audio encoding, see e.g. https://wiki.hydrogenaud.io/index.php?title=Bitrate
bpp = bits per pixel, not bytes. At 1080p, "0.05-0.1 bpp" is 13-26 KB. Much smaller than what you were testing. Might want to recheck your sizes, if you are actually looking at 0.5 bpp it would not surprise me at all that you found JPEG XL superior.
At very small sizes like 0.1 bpp the results are debatable, but I think AVIF is a pretty clear winner if you aren't too bothered by blurring. Samples at 0.15 bpp:
https://afontenot.github.io/image-formats-comparison/#air-fo...
https://afontenot.github.io/image-formats-comparison/#citroe...
https://afontenot.github.io/image-formats-comparison/#festa-...