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International
Standard
ISO/IEC 18181-1
Second edition
Information technology — JPEG XL
image coding system —
2024-07
Part 1:
Core coding system
Technologies de l'information — Systѐme de codage d'images
JPEG XL —
Partie 1: Système de codage de noyau
Reference number
© ISO/IEC 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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© ISO/IEC 2024 – All rights reserved
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions .1
3.2 Inputs .2
3.3 Processes .3
3.4 Image and codestream organization .4
3.5 Abbreviated terms .5
4 Conventions . 5
4.1 Mathematical symbols .5
4.2 Functions .6
4.3 Operators .6
4.4 Pseudocode .7
5 Functional concepts . . 8
5.1 Image organization .8
5.2 Mirroring .8
5.3 Group splitting .8
5.4 Codestream organization .8
6 Encoder requirements . 9
7 Decoder requirements. 9
Annex A (normative) Codestream overview . 10
Annex B (normative) Header syntax .11
Annex C (normative) Entropy decoding . 14
Annex D (normative) Image header .20
Annex E (normative) Colour encoding .25
Annex F (normative) Frame header .34
Annex G (normative) Frame data sections . 41
Annex H (normative) Modular .45
Annex I (normative) VarDCT .55
Annex J (normative) Restoration filters .70
Annex K (normative) Image features . 74
Annex L (normative) Colour transforms .82
Annex M (normative) Profiles and levels .85
Annex N (normative) Extensions .87
Annex O (informative) Encoder overview .88
Bibliography .91
© ISO/IEC 2024 – All rights reserved
iii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations,
governmental and non-governmental, in liaison with ISO and IEC, also take part in the work.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of document should be noted. This document was drafted in accordance with the editorial rules of the ISO/
IEC Directives, Part 2 (see www.iso.org/directives or /members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any
claimed patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had
received notice of (a) patent(s) which may be required to implement this document. However, implementers
are cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents and https://patents.iec.ch. ISO and IEC shall not be held
responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
In the IEC, see /understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
This second edition cancels and replaces the first edition (ISO/IEC 18181-1:2022), which has been technically
and editorially revised. It also incorporates the Amendment ISO/IEC 18181-1:2022/Amd 1:2022.
The main changes are as follows:
— technical corrections and clarifications, in particular to correct the values of various constants, correct
errors in pseudocode, and clarify ambiguities in order to remove discrepancies between this document
and ISO/IEC 18181-3 and ISO/IEC 18181-4;
— a thorough update of the document structure in order to improve clarity of presentation and to obtain a
more logical ordering of the material from the point of view of decoder implementation.
A list of all parts in the ISO/IEC 18181 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
/national-committees.
© ISO/IEC 2024 – All rights reserved
iv
International Standard ISO/IEC 18181-1:2024(en)
Information technology — JPEG XL image coding system —
Part 1:
Core coding system
1 Scope
This document specifies a set of compression methods for coding one or more images of bi-level, continuous-
tone greyscale, or continuous-tone colour, or multichannel digital samples.
This document:
— specifies decoding processes for converting compressed image data to reconstructed image data;
— specifies a codestream syntax containing information for interpreting the compressed image data;
— provides guidance on encoding processes for converting source image data to compressed image data.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 15076-1, Image technology colour management — Architecture, profile format and data structure — Part 2:
Based on ICC.1:2022
ISO/IEC 60559, Information technology — Microprocessor Systems — Floating-Point arithmetic
IEC 61966-2-1, Multimedia systems and equipment — Colour measurement and management — Part 2-1: Colour
management — Default RGB colour space — sRGB
ITU-R BT.2100-2, Image parameter values for high dynamic range television for use in production and
international programme exchange
ITU-R BT.709-6, Parameter values for the HDTV standards for production and international programme
exchange
IETF RFC 7932:2016, Brotli Compressed Data Format
SMPTE ST 428-1, D-Cinema Distribution Master — Image Characteristics
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org
© ISO/IEC 2024 – All rights reserved
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