File extension

.jxl

JPEG XL image format

.jxl files are JPEG XL images: a royalty-free image format standardized as ISO/IEC 18181 that supports lossy and lossless compression, HDR, animation, and lossless recompression of existing JPEG files.

Known meanings

Formats and reference material for .jxl

JPEG XL image format

Modern image format with lossy and lossless modes, wide gamut/HDR, animation, and JPEG recompression

  • 2d-graphics
  • Joint Photographic Experts Group (ISO/IEC JTC 1/SC 29/WG 1)
Open link

Details

Format notes

JPEG XL

JPEG XL is an image format developed by the JPEG committee as a general purpose successor to JPEG. It is specified in ISO/IEC 18181 and was designed to cover photographic and synthetic images, high bit depths, wide color gamuts and HDR, alpha, layers, and animation in a single format. Its reference implementation, libjxl, is open source and the format is intended to be royalty-free.

Technical Structure

JPEG XL has two coding modes. VarDCT is a lossy mode based on variable-size discrete cosine transforms, and Modular is a mode used for lossless coding and for images with sharp edges or limited palettes. A distinctive feature is reversible transcoding of existing JPEG files: the JPEG data is recompressed into JXL and can be restored bit-exactly, typically at a smaller size.

A file is either a bare codestream starting with the bytes FF 0A, or an ISO base media style container starting with the 12-byte signature 00 00 00 0C 4A 58 4C 20 0D 0A 87 0A (a “JXL “ box). The container can carry Exif, XMP, and the JPEG reconstruction data next to the codestream. The media type is image/jxl.

Adoption

Support has grown across image libraries and tools such as libjxl, ImageMagick, and GIMP, and several operating systems and browsers have added or experimented with decoders. Browser support has changed over time, so check current compatibility before using JXL for web delivery.

Preservation Notes

JXL can store images losslessly, and JPEG recompression allows smaller storage without loss for existing JPEG archives. Record the coding mode (VarDCT or Modular), bit depth, color encoding, and whether the file is a recompressed JPEG. Decoders should limit image dimensions and memory use when handling untrusted files.

Further Reading

  • JPEG XL overview (JPEG committee): https://jpeg.org/jpegxl/
  • libjxl reference implementation: https://github.com/libjxl/libjxl