ProdigalFrog

Existing browsers and apps can’t render jpegXL without adding a new decoder.

Why is that a negative?

Jpeg XL isn’t backwards compatible with existing JPEG renderers. If it was, it’d be a winner.

According to the video, and this article, JPEG XL is backwards compatible with JPEG.

But I'm not sure if that's all that necessary. JPEG XL was designed to be a full, long term replacement to JPEG. Old JPEG's compression is very lossy, while JPEG XL, with the same amount of computational power, speed, and size, outclasses it entirely. PNG is lossless, and thus is not comparable since the file size is so much larger.

JPEG XL, at least from what I'm seeing, does appear to be the best full replacement for JPEG (and it's not like they can't co-exist).

TL:DW, JPEG is getting old in the tooth, which prompted the creation of JPEG XL, which is a fairly future-proof new compression standard that can compress images to the same file size or smaller than regular JPEG while having massively higher quality.

However, JPEG XL support was removed from Google Chrome based browsers in favor of AVIF, a standalone image compression derived from the AV1 video compression codec that is decidedly not future-proof, having some hard-coded limitations, as well as missing some very nice to have features that JPEG XL offers such as progressive image loading and lower hardware requirements. The result of this is that JPEG XL adoption will be severely hamstrung by Google’s decision, which is ultimately pretty lame.