Comment by TacticalCoder

Without taking into account whether JPEG XL shines on its own or not (which it may or may not), JPEG XL completely rocks for sure because it does this:

    .. $  ls -l a.jpg && shasum a.jpg
    ... 615504 ...  a.jpg
    716744d950ecf9e5757c565041143775a810e10f  a.jpg

    .. $  cjxl a.jpg a.jxl
    Read JPEG image with 615504 bytes.
    Compressed to 537339 bytes including container

    .. $  ls -l a.jxl
    ... 537339 ... a.jxl

But, wait for it:

    .. $  djxl a.jxl b.jpg
    Read 537339 compressed bytes.
    Reconstructed to JPEG.

    .. $  ls -l b.jpg && shasum b.jpg
    ... 615504 ... b.jpg
    716744d950ecf9e5757c565041143775a810e10f  b.jpg

Do you realize how many billions of JPEG files there are out there which people want to keep? If you recompress your old JPEG files using a lossy format, you lower its quality.

But with JPEG XL, you can save 15% to 30% and still, if you want, get your original JPG 100% identical, bit for bit.

That's wonderful.

P.S: I'm sadly on Debian stable (12 / Bookworm) which is on ImageMagick 6.9 and my Emacs uses (AFAIK) ImageMagick to display pictures. And JPEG XL support was only added in ImageMagick 7. I haven't looked more into that yet.