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JPEG XL is worth mentioning here. It includes a JPEG1 repacker (Brunsli) that saves about 20% and allows recovering the original file exactly. All that existing JPEG1 content isn't going anywhere, so that seems good. It has some other neat features like the ability to mix a DCT-based codec with lossless (modular) mode in an image. Its lossless/modular mode (successor to FLIF/FUIF) is interesting on its own.

It can be illuminating to stretch codecs a bit past the visually-indistinguishable threshold, both to better nail down where that threshold is and to see how annoying the artifacts you end up with are. Lots of comparisons you can do; this is a fun one: https://encode.su/threads/3108-Google-s-compression-proje%D1...

At very few bits-per-pixel like the first (bridge) image, everything has some artifacts. On that image AVIF tends to just blur lower contrast areas, whereas HEIC produces some visible ringing (faint lines that weren't there before) around the bridge. Unlike JXL, AVIF and HEIC both have spatial prediction (extend pixels above/to the left of this block in whatever direction), which is particularly helpful with straight sharp lines like the bridge image happens to have. I wouldn't put too much stock in results on that one image, but I do like being able to judge results subjectively.

(FWIW, a presentation on JPEG XL suggested they were targeting the equivalent of ~2bpp JPEG quality[0], so perhaps performance in this super-low range wasn't as much of a priority.)

Anyway, I hope both these formats get wide support, because they each have clear benefits in some application: JXL's include the upgrade path for JPEG1 content and the multiple modes, and AVIF may be able to salvage a bit more quality at super low bitrates. AV1 (on which AVIF is based) has wide industry backing, and the JPEG XL effort is also going for a royalty-free codec and has support from Google, so hopeful they actually will be usable relatively soon.

(Although HEIC's images are OK and it has Apple's support already, it's patent-encumbered, limiting what you or I can do with it.)

[0]: https://www.spiedigitallibrary.org/conference-proceedings-of...

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