JPEG XL
JPEG XL logo.svg
Filename extension
.jxl
Internet media type
image/jxl[a]
Magic numberFF 0A or 00 00 00 0C 4A 58 4C 20 0D 0A 87 0A[2]
Developed by
Type of formatLossy/lossless bitmap image format
Extended from
StandardISO/IEC 18181[4]
Open format?Yes (royalty-free)
Website

JPEG XL is a royalty-free raster-graphics file format that supports both lossy and lossless compression. It is designed to outperform existing raster formats and thus become their universal replacement.[5]

Name

The name consists of JPEG (for the Joint Photographic Experts Group, which is the committee which designed the format), X (part of the name of several JPEG standards since 2000: JPEG XT, JPEG XR, JPEG XS), and L (for long-term). The L was included because the authors' intention is for the format to replace the legacy JPEG and last as long too.[6]

Authors

The main authors of the specification are Jyrki Alakuijala, Jon Sneyers, and Luca Versari. Other collaborators are Sami Boukortt, Alex Deymo, Moritz Firsching, Thomas Fischbacher, Eugene Kliuchnikov, Robert Obryk, Alexander Rhatushnyak, Zoltan Szabadka, Lode Vandevenne, and Jan Wassenberg.

History

In August 2017, JTC1 / SC29 / WG1 (JPEG) published a call for proposals for JPEG XL, the next generation image encoding standard.[7] The proposals were submitted by September 2018, leading to a committee draft in July 2019.[8] It was mainly based on a combination of a proposal called PIK,[9] submitted by Google, and a proposal called FUIF[10] — itself based on FLIF — submitted by Cloudinary.

The bitstream was informally frozen on 24 December 2020 with the release of version 0.2 of the libjxl reference software.[11] The file format and core coding system were formally standardized on 13 October 2021 and 30 March 2022 respectively.[4][12]

Description

The JPEG XL call for proposals[7] talks about the requirement of a next generation image compression standard with substantially better compression efficiency (60% improvement) comparing to JPEG. The standard is expected to outperform the still image compression performance shown by HEIC, AVIF, WebP, and JPEG 2000. It also provides efficient lossless recompression options for images in the traditional/legacy JPEG format.

JPEG XL supports lossy compression and lossless compression of ultra-high-resolution images (up to 1 terapixel), up to 32 bits per component, up to 4099 components (including alpha transparency), animated images, and embedded previews. It has features aimed at web delivery such as advanced progressive decoding[13] and minimal header overhead, as well as features aimed at image editing and digital printing, such as support for multiple layers, CMYK, and spot colors. It is specifically designed to seamlessly handle wide color gamut color spaces with high dynamic range such as Rec. 2100 with the PQ or HLG transfer function.

Features

The main features are:[14][15][16]

Technical details

JPEG XL codec architecture diagram
JPEG XL codec architecture diagram

JPEG XL is based on ideas from Google's PIK format and Cloudinary's FUIF format (which was in turn based on FLIF).[19]

The format is mainly based on two encoding modes:

Any additional/extra channels (e.g. alpha, depth, thermal, spot colors, etc.) are always encoded in the modular mode. It was based on FUIF, combined with elements of lossless PIK, lossless WebP, and new ideas that have been developed during the collaborative phase of the standardization process.[21] Modular mode allows lossy compression with the help of the modified Haar transform called "squeeze" which has progressive properties, quality of the image increases with the amount of data loaded.

One of the ways VarDCT-based images can be loaded more progressively is by saving the DC coefficients in a separate "DC frame" that uses modular squeeze: allowing previews corresponding to 1:16, 1:32 etc subsampled images. A squeeze transform can also be used to encode the alpha channel progressively together with VarDCT-encoded color channels, making both modes work in tandem.

JPEG XL defaults to a visually near-lossless setting that still provides good compression.[17]

These modes can be assisted by separate modeling of specific image features called:

JPEG XL codec can losslessly transcode a widely-supported subset of JPEG files, by directly copying JPEG's DCT block coefficients to 8×8 VarDCT blocks, making smaller file sizes possible due to JPEG XL's superior entropy coding. This process is reversible and it allows for the original JPEG file to be reconstructed bit-for-bit, although constraints limit support for some files.[22]

Prediction is run using a pixel-by-pixel decorrelator without side information, including a parameterized self-correcting weighted ensemble of predictors. Context modeling includes specialized static models and powerful meta-adaptive models that take local error into account, with a signaled tree structure and predictor selection per context. Entropy coding is LZ77-enabled and can use either asymmetric numeral systems or Prefix codes (useful for low-complexity encoders, or reducing the overhead of short streams).[citation needed]

Animated (multi-frame) images do not perform advanced inter-frame prediction, though some rudimentary inter-frame coding tools are available:

Industry support and adoption

Besides Cloudinary and Google (originally), throughout JPEG XL's preliminary implementation in web browsers, various representatives of well-known industry brand names have publicly voiced support for JPEG XL as their preferred choice, including Facebook,[24][25] Adobe,[26][27] Intel and the Video Electronics Standards Association,[28][29] The Guardian,[30][31] Flickr and SmugMug,[32] Shopify,[33] the Krita Foundation,[34] and Serif Ltd.[35]

Software

Codec implementations

JPEG XL Reference Software (libjxl)
Initial releaseDecember 27, 2019; 3 years ago (2019-12-27)[36]
Stable release
0.7 / September 21, 2022; 3 months ago (2022-09-21)
Repositoryhttps://github.com/libjxl/libjxl[37] Edit this on Wikidata
Written inC++
Operating system
LicenseNew BSD License (previously Apache License 2.0)
Websitejpeg.org/jpegxl Edit this on Wikidata

Official support

Unofficial or indirect support

Preliminary web browser support

Support for JPEG XL in Chromium and Chrome web browsers was introduced for testing April 1st, 2021[67] and removed on December 9th, 2022.[68] The Chrome team cited a lack of interest from the ecosystem, insufficient improvements, and a wish to focus on improving existing formats, as reasons for the removal.[67][69] The decision was met with opposition from the community, with many voicing support for JPEG XL on Chromium's bug tracker.[67][70][69] Jon Sneyers, co-author of the JPEG XL spec, has questioned the conclusions drawn by the Chrome team, saying: "I think there has been an unfortunate misinterpretation of the data ... which has unfortunately lead [sic] to an incorrect decision."[71]

Standardization status

Common Name Part First public release date (First edition) ISO/IEC Number Formal Title
JPEG XL Part 1 30 March 2022 ISO/IEC 18181-1 JPEG XL Image Coding System — Part 1: Core coding system[4]
Part 2 13 October 2021 ISO/IEC 18181-2 JPEG XL Image Coding System — Part 2: File format[12]
Part 3 3 October 2022 ISO/IEC 18181-3 JPEG XL Image Coding System — Part 3: Conformance testing
Part 4 5 August 2022 ISO/IEC 18181-4 JPEG XL Image Coding System — Part 4: Reference software

Rivals

Notes

  1. ^ This is unofficial, but de-facto. See the official list of media types.[1]

References

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