> This tells me you don't know how codecs work Laughable. My conservative estimate is that a few-MP image with all but a smallish region encoded using skip bl

> This tells me you don't know how codecs work Laughable. My conservative estimate is that a few-MP image with all but a smallish region encoded using skip blocks will spend a few KiB on that. This is very expensive compared to sending only a bounding box, hence it is unattractive for purposes of updating small regions with a whole-image layer. I am glad to hear AVIF progressive has improved. But note that my original comment was: I find it misleading to call AVIF's "up to four passes" "very flexible". I believe that stands: contrasting the flexibility of (purpose-built) JPEG XL vs. the fairly strict limitations (inherited from video) of AVIF, I am astonished anyone would still call the latter "very flexible" by comparison.