This is not complete! Do not run it on files you care about!
This is a FUSE filesystem, which converts images from JPEG XL to JPEG on the fly as they are being read by applications. This takes advantage of a special feature of JPEG XL where you can losslessly recompress a JPEG into JPEG XL, which shrinks it by roughly 20% while keeping the ability to restore a bit-for-bit identical copy of the original JPEG file. This means that if you have a large collection of JPEG files, you can reduce your storage needs even if not all the software you use supports JPEG XL yet.
Say you have a folder full of images from a camera: original/DSC_XXXX.jpg. You can run a script to convert them all to JPEG XL, and then delete the originals: jxl/DSC_XXXX.jxl. Then, if you create an empty directory and run jxl-fuse jxl mountpoint, mountpoint will appear to contain all your original JPEG files; in reality they are converted on the fly when you read them.
- if an error is encountered reading a file to check whether it is valid JPEG XL, the file is ignored for purposes of directory listings
- a symlink's filename appears unchanged even if the file it points to is a recompressed JPEG
- JPEG XLs that are not recompressed JPEG still appear with the extension changed to
.jpg, but the file contents are read as JPEG XL - symlinks are not handled at all