What is JPEG XL, and can you use it yet?

What JPEG XL is

JPEG XL (file extension .jxl) is an image format standardised in 2021 by the JPEG committee as a successor to JPEG. It offers lossy and lossless compression, transparency, high bit depths, HDR, progressive decoding and very large image dimensions. Lossy JPEG XL files are typically 20 to 60 percent smaller than JPEG at similar quality, depending on the image and settings.

Its unusual trick: repacking JPEGs

The format can take an existing JPEG and store it losslessly in a smaller file, with the option to rebuild the original JPEG bit for bit later. That makes it attractive for archives full of old JPEGs.

The converter here does not use that mode. JPG to JXL decodes the JPG to pixels and encodes them again, either lossy or with the Lossless option under More options. Lossless keeps the decoded pixels exactly, but the file is usually larger than the JPG you started with and cannot be turned back into the original JPG bytes.

Where you can open it

• Safari 17 and later on macOS and iOS displays JPEG XL.
• Recent versions of GIMP and a growing number of other editors and viewers can open it.
• Support in Chrome, Edge and Firefox has long been missing or hidden behind settings, and it is changing. Check current browser support before serving JPEG XL on a website, and always provide a fallback.

When to use it

• Archiving high quality masters, when you control the software that will read them.
• Workflows between apps that support it, where the lossless mode and high bit depth help.
• Not yet for email, upload forms or social media, where it will often be rejected. Convert to JPG first with JXL to JPG.

How it runs here

Encoding and decoding use libjxl compiled to WebAssembly, loaded only when a JPEG XL file or output is involved, and the conversion happens on your device. Image Inspector reports the real format of a file from its bytes, which helps when a file named .jpg turns out to be something else.