A new PNG spec

JPEG XL is not a "variant", it is a completely new algorithm that is also fully backwards-compatible with every single JPEG already out there, of which there are probably billions at this point.

It also has pretty much every feature desired in an image standard. It is future-proofed.

You can losslessly re-compress a JPEG into a JPEG-XL file and gain space.

It is a worthy successor (while also being vastly superior to) JPEG.

I was referring to the new PNG, not to JPEG XL.

Is there any risk that if I open a JPEG-XL in something that knows what a JPEG is but not what a JPEG-XL is and then save it, it'll get lossy compressed? Backwards compatibility is awesome, but I know that if I save/upload/share/copy a PNG, it shouldn't change without explicit edits, right?

> You can losslessly re-compress a JPEG into a JPEG-XL file and gain space.

Is that gained space enough to account for the fact you now have 2 files? Sure, you can delete the original jpg on the local system, but are you going to purge your entire set of backups?

Looking at TFA, it's placing in the spec a few things that are already widely stacked onto the format (such as animation). This is a very sensible update, and backwards compatible with existing PNG.

if you do not want to delete the original jpeg, there is no point in converting them to jpeg xl I would say.

Unless serving jxl and saving bandwidth, while increasing your total storage, is worth it to you.

a sw that does not know what jpeg xl is, will not be able to open jxl files. How would it?

Not sure what the previous poster meant with “backward compatible” here. jxl is a different format. It can include every information a jpeg includes, which then maybe qualifies as “backward compatible” but it still is a different format.

Not sure expanding PNG capabilities is sensible, looking at the overall landscape of image formats.

JPEG XL has the mode that in layman's word, allow bit-by-bit round-trip with JPEG.

Original JPEG -> JPEG XL -> Recreated JPEG.

Sha256(Original JPEG) == Sha256(Recreated JPEG).

That's what people meant by "backward compatible".

That’s not “backwards compatible”, but “round tripable” or “lossless reencode”

Ah, got it. I assumed it was a losselessly compressed JPEG with metadata telling modern software not to compress differently but that older software would open as a normal JPEG, but I guess they meant something else with "backward compatible".

The capabilities are already expanded in most common implementations. This update is largely blessing those features as officially "standard".

Yes the whole point of lossless re-compression is that you do not need to keep the original JPEGs. Of course you don't need to "purge" backups, just let them rotate out normally.

Also backup storage is usually cheaper than something that needs to have fast access speeds.

For people that shoot digital cameras saving as JPEG, it will a very cocky suggestion to tell them to toss out their camera original files!

You'll know JPEG-XL if real when camera manufactures allow for XL acquisition instead of legacy JPEG only.