I'm not a mathematician but...
its hosted on a raspberry pi and is front page of HN...
Amazingly enough the page seems to be updated very recently ("November 2021", which was not present back in March [1]).
[1] https://web.archive.org/web/20210305192950/https://pagepipe....
Also while AVIF supports lossless images, its lossless compression is known to be weak and can be even inferior to PNG, while the WebP lossless mode is a dedicated algorithm and almost guaranteed to be better than PNG. This is a reason why JPEG XL can be better than AVIF in the long term, where AVIF is just another intra-frame format extracted from video codecs while JPEG XL is explicitly built to support both use cases.