I believe JPEG-XL to be the best image compression format available today. I followed its beginnings as FLIF, which at the time had the best compression ratios around. It eventually merged with Pik to be selected as the new JPEG standard. The codec has an insanely rich feature set, one that can even encode stunning art pieces in a few hundred bytes. Today, the reference implementation is also the best available by some reckonings, but not all (see a rebuttal to that last link here). In my experience, lossless transcoding from JPEG to JPEG-XL usually decreases an image's size by well over 30%, and the single-threaded decoding speed is substantially faster than AVIF, plus it's progressive, meaning the image can be displayed at a lower quality while it is still being downloaded.
Unfortunately, JPEG-XL has been seeing much slower adoption than other formats such as WEBP and AVIF. If you use any browser except Safari, it is very unlikely you were able to see my picture on your first try. It is not because these formats are better; WEBP came earlier and is pretty straightforwardly inferior, while AVIF is comparable to JPEG-XL in most dimensions, with a reduced feature set that makes it unsuitable for some applications (especially photography). AVIF is the only real competitor JPEG-XL has today, in terms of technical merits. Arguably, JPEG-XL is "more experimental", in the sense that the reference implementation has not yet had its 1.0 release, while the AVIF reference implementation had its 1.0 release in late 2023.
You may think that JPEG-XL's "experimental" nature is why it has not enjoyed widespread adoption. Not so. In fact, chrome stabilized AVIF support in 2020, back when the AVIF decoder was in version 0.8.4 and the format itself had been finalized for about 1.5 years. Experimental support for JPEG-XL was added in 2021, a few months after the format was finalized, and it appeared to be on the long road to being available in all major browsers. In late 2022, the chrome team abruptly decided to stop supporting it, citing a lack of interest from users as well as the development burden. This was widely criticized.
The true reason could not be more obvious. Some of the senior chrome devs, for some reason or another, don't want JPEG-XL, even though it was partly designed by Google researchers. This may be simply because they are wary of adding more libraries. They may be hoping that hardware acceleration meant for AV1 video will help with decoding AVIF files (this is unlikely). It may be because the chrome devs have links to Alliance for Open Media, which publishes the AVIF standard. The actual reason doesn't really matter; what matters is that google, because of their various monopolies, single-handedly killed the JPEG-XL format, through a process that happened behind closed doors and without input from anyone else.
This is not the first time google has decided single-handedly what the web will look like. They continue to push WEBP, much to the chagrin of anyone interested in image quality or interoperabily. They push AMP, which while it has some technical merits, is also deeply integrated with google's ad and tracking businesses. And while we're on the subject of ads and tracking, google has consistently tried to limit users from using ad blockers on google chrome, and chrome tracks your every move online.
This format war is far from over. Apple seems to have decided JPEG-XL is the best for their cameras, and a partial decoder is enabled universally in the Apple ecosystem, which is a major reason why the format is not completely dead. Firefox does have (incomplete and off-by-default) support, and has plans to stabilize a rust version of the decoder in the future. Big tech companies using their monopolies to take away the end user's agency is nothing new. Really it's as old as the computer business itself. But, there's a secret they don't want you to know: We don't have to put up with it.
Right this very moment, you can head over to waterfox.net, download it, and look at the beautiful photo of me on my website. While firefox has many, many imperfections, it has one huge advantage over chrome: the source is free. That means that if tomorrow the Mozilla foundation collapsed, or unilaterally made a bad decision, there would still be dozens of forks with improvements and modifications ready to be used by anyone. It might be a little different to what you're used to, and you may find that some parts of the google ecosystem you rely on are missing, but maybe it's worth asking, why do we rely on them? If these programs are created for the purpose of exploiting us, why do we find it so hard to stop using them?
Long story short, putting a .jxl file as my headshot on my website is a form of protest about a small thing that irks me, but that small thing is part of a large thing that is probably an existential threat to the human race. If you really want to see my face in the chrome web browser, here it is:
