avif also supports lossless, but it's so inefficient it might as well not exist.

Lossless webp is a completely different image format compared to lossy webp, even though they come under the same file extension. Unlike lossy webp, it's a good image format that has excellent compression ratio compared to png. I've often been using it for screenshots to avoid damaging text clarity and still maintain acceptable file size.

jxl has excellent support for both lossy and lossless cases, and can replace both lossy avif (even if somewhat less efficient at low file sizes), and lossless webp.

Note also that converting jpeg to jxl is 100% reversible, you can convert it back to exactly the same image (byte for byte identical) if you need to.

▲ encrypted_bird 5 hours ago | parent [-]

>Note also that converting jpeg to jxl is 100% reversible, you can convert it back to exactly the same image (byte for byte identical) if you need to.

Speaking as someone who loves JXL, I have a serious question: I once used ImageMagick to convert a JPG to a JXL, and then back to JPG, and the final JPG was a noticeably different file size compared to the source JPG.

What am I misunderstanding here?

	▲	farlight 5 hours ago \| parent \| next [-]
		Not sure imagemagick supports lossless transcoding. This old discussion from 2021 mentions that it didn't (in 2021): https://github.com/dlemstra/Magick.NET/discussions/872 cjxl / djxl do lossless transcode reliably when called with all defaults (no arguments). Just re-checked: `$ cjxl src.jpg out.jxl (some output) $ djxl out.jxl rev.jpg (more output) $ cmp src.jpg rev.jpg (no output: files identical)`
	▲	pxoe 5 hours ago \| parent \| prev \| next [-]
		JPEG to JXL transcoding and JXL to JPEG reconstruction are different from converting an image in either direction, it's gonna be a specific option (in something like xl-converter), so maybe it wasn't what was used and it was just a "reencode" into jxl and then into jpeg.
	▲	dchest 5 hours ago \| parent \| prev \| next [-]
		It probably used pixel-by-pixel conversion (decode input format -> encode output format), which is lossy, not the libjxl native way to convert JPEG (it needs to know about the original JPEG data, not the raw image data).
	▲	shakna 4 hours ago \| parent \| prev [-]
		Image Magick re-encodes into an internal format, before output. If reproducibility is the goal, I'm afraid it just isn't the right tool. (The IR used to be PixelPacket. Not sure how modern versions handle it.)