JPEG XL support for PDF and comic book files

[golemusu]

I am doing this early as PDF standard has not yet gained PDF support but according to couple of articles it is coming soon. Please add it ASAP when possible. JPEG XL encoding can reduce size of PDF documents by 70% without visible quality loss. In certain scenarios up to 90%

For same reason it would be nice to have it in comic book files (.cbz, .cb7, etc...). And yes I know avif support is already there but JXL is superior in majority of use cases (especially in encoding speed).

Related link below:

https://www.theregister.com/2025/11/10/another_chance_for_jpeg_xl/

[GitHubRulesOK]

The new experimental object filter for PDF is BrotliDecode
AND as with all PDF object compactions can make files bigger and slower because of resource overheads.
Thus every time the filter is added to an object it adds an extra 20 to 40 bytes to every stream (not a lot but counterproductive in smaller edge cases.)
It pays significant byte differences the more textual a PDF is because its DICTIONARY focus is biased to HTML words.

For images it has to double bag them (to be simply added) thus an image is still the same speed as before but takes longer to unpack that wrapper. OR it has to inFlate the stream then Encode it so it is not a PNG or JPEG but a Brotli STREAM that is slower than a normal deFlated image.

For Comic Book Format the whole point is the compaction is the zip or similar wrapper, so the time taken to unzip an image then needs the decoding time ADDED to that, The fastest is standard JPEG in ZIP same as either in a PDF where Flate=zip is used.

[GitHubRulesOK]

Since SumatraPDF is around the core rendering of MuPDF this was covered before that if MuPDF uses non TurboJPEG formats they will be inherited by updates thus closing as duplicate of #1943

Unknown if BrotliEncode will be PDF 2.1 but Artifex comment was

If JPEG XL was added to the e.g. PDF 2.2 specification then the situation
would be very different we'd essentially be forced to support it to gain
full support for one of our core file formats.

Related #960 and #4729