[lifthrasiir]

It's crucial to distinguish JPEG the file format (now retronymed as JPEG 1) and JPEG the standardization group.

JPEG XL is officially blessed by JPEG but otherwise irrelvant here, even though non-progressive JPEG 1 files can be losslessly recompssed into JPEG XL by its design. The main role of JPEG here was to specify explicit goals for JPEG XL proposals [1]. Interestingly enough, the JPEG 1 recompression was not a part of that call for proposals back then. JPEG XL is otherwise a completely different format with much better compression algorithms, so should be the image format for pretty much all uses once popularized.

Ultra HDR [2] is an extension to the JPEG 1 format, which depends on XMP and the CIPA Multi-Picture Format. This kind of extension was not the first, even JPEG the group itself had a similar extension called JPEG XT which was never popular! (If you don't know much about JPEG, APNG was a similarly designed extension to PNG which eventually became a part of PNG.) Naturally Ultra HDR files cannot be smaller than ordinary JPEG 1 files, so can't fulfill Samsung's needs.

[1] https://jpeg.org/downloads/jpegxl/jpegxl-cfp.pdf

[2] https://developer.android.com/media/platform/hdr-image-forma...

[JyrkiAlakuijala]

I proposed lossless JPEG1 recompression as a functionality of JPEG XL after PIK/FUIF were chosen as a platform. The committee saw this of great value and we decided together this as an additional requirement after the competition was completed. We had a lot of experience of this in brunsli and were sure that we can deliver a good solution for it.