JPEG XL reference implementation

This repository contains a reference implementation of JPEG XL (encoder and decoder), called libjxl. This software library is used by many applications that support JPEG XL.

JPEG XL was standardized in 2022 as ISO/IEC 18181. The core codestream is specified in 18181-1, the file format in 18181-2. Decoder conformance is defined in 18181-3, and 18181-4 is the reference software.

The library API, command line options, and tools in this repository are subject to change, however files encoded with cjxl conform to the JPEG XL specification and can be decoded with current and future djxl decoders or the libjxl decoding library.

Installation

In most Linux distributions, installing libjxl is just a matter of using the package management system. For example in Debian-based distributions: apt install libjxl-tools will install cjxl and djxl and other tools like benchmark_xl are available in the package libjxl-devtools. On MacOS, you can use Homebrew: brew install jpeg-xl.

From the releases page the following can be downloaded:

• Windows binaries
• Debian and Ubuntu .deb packages

Of course you can also build libjxl from sources.

Usage

To encode a source image to JPEG XL with default settings:

cjxl input.png output.jxl

The desired visual fidelity can be selected using the --distance parameter (in units of just-noticeable difference, where 0 is lossless and the most useful lossy range is 0.5 .. 3.0), or using --quality (on a scale from 0 to 100, roughly matching libjpeg). The encode effort can be selected using the --effort parameter.

For more settings run cjxl --help or for a full list of options run cjxl -v -v --help.

To decode a JPEG XL file run:

djxl input.jxl output.png

When possible cjxl/djxl are able to read/write the following image formats: .exr, .gif, .jpeg/.jpg, .pfm, .pgm/.ppm, .pgx, .png. Specifically for JPEG files, the default cjxl behavior is to apply lossless recompression and the default djxl behavior is to reconstruct the original JPEG file (when the extension of the output file is .jpg).

Benchmarking

For speed benchmarks on single images in single or multi-threaded decoding djxl can print decoding speed information. See djxl --help for details on the decoding options and note that the output image is optional for benchmarking purposes.

For more comprehensive benchmarking options, see the benchmarking guide.

Library API

Besides the libjxl library API documentation, there are example applications and plugins that can be used as a reference or starting point for developers who wish to integrate libjxl in their project.

License

This software is available under a 3-clause BSD license which can be found in the LICENSE file, with an "Additional IP Rights Grant" as outlined in the PATENTS file.

Please note that the PATENTS file only mentions Google since Google is the legal entity receiving the Contributor License Agreements (CLA) from all contributors to the JPEG XL Project, including the initial main contributors to the JPEG XL format: Cloudinary and Google.

Additional documentation

Codec description

• JPEG XL Format Overview
• Introductory paper (open-access)
• XL Overview - a brief introduction to the source code modules
• JPEG XL white paper
• JPEG XL official website
• JPEG XL community website

Development process

• More information on testing/build options
• Git guide for JPEG XL - for developers
• Fuzzing - for developers
• Building Web Assembly artifacts
• Test coverage on Codecov.io - for developers
• libjxl documentation on readthedocs.io

Contact

If you encounter a bug or other issue with the software, please open an Issue here.

There is a subreddit about JPEG XL, and informal chatting with developers and early adopters of libjxl can be done on the JPEG XL Discord server.