[Feature Request] JXL support

[lordkitsuna]

Hello i would like to request, support for the JXL image format. Almost no manga/doujinshi site i know of uses it directly however this would allow users to do it themselfs. JXL has the potential to save a substantial amount of space on large collections. even if the source files were jpg, JXL supports a lossless transition from JXL to the new format with a potential for up to 30% smaller file. and when talking about PNG the space savings can be massive.

as an example i converted a test library with just shy of 800 random works from nhentai and got the following results

Original Library Size: 14.5 GiB (15,546,233,934)
JXL Library Size: 11.0 GiB (11,850,327,695)

This was with lossless JXL as in the mathematically lossless mode being used to ensure no quality loss in the conversion. thats normal for re-compressing jpg but i also used lossless for any PNG in the set as well meaning it could have realistically been smaller had i used something like -d 0.8 for a visually but not mathematically lossless. despite that i still saved 3.5GB which on a phone can be a nice chunk saved

[RobbWatershed]

Thanks for your suggestion 👍 I'll see what I can do.