ISO/IEC 18181-1:2022

INTERNATIONAL ISO/IEC
STANDARD 18181-1
First edition
2022-03
Information technology — JPEG XL
image coding system —
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 2022
© ISO/IEC 2022
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 2022 – All rights reserved

Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Data storage . 2
3.2 Inputs . 2
3.3 Processes . 3
3.4 Image organization . 4
3.5 DCT . 5
4 Abbreviated terms . 6
5 Conventions . 6
5.1 Mathematical symbols . 6
5.2 Functions . 6
5.3 Operators . 7
5.4 Pseudocode . 7
6 Functional concepts . .8
6.1 Image organization . 8
6.2 Group splitting . 8
6.3 Codestream and bitstream . 9
6.4 Multiple frames . 10
6.5 Mirroring . 10
7 Encoder requirements .10
8 Decoder requirements.10
9 Codestream .10
9.1 Syntax . 10
9.1.1 Reading a field . 11
9.1.2 Initializing a field . 11
9.2 Field types . 11
9.2.1 u(n) . 11
9.2.2 U32(d0, d1, d2, d3) . 11
9.2.3 U64() . 11
9.2.4 Varint() . 12
9.2.5 U8() . 12
9.2.6 F16() . 12
9.2.7 Bool() .12
9.2.8 Enum(EnumTable) .12
9.2.9 ZeroPadToByte() . 13
9.3 Structure . 13
10 Decoding process .13
Annex A (normative) Headers .15
Annex B (normative) ICC profile . .25
Annex C (normative) Frames .32
Annex D (normative) Entropy decoding .58
Annex E (normative) Weighted predictor .67
Annex F (normative) Adaptive quantization . .70
Annex G (normative) Chroma from luma.71
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© ISO/IEC 2022 – All rights reserved

Annex H (normative) Extensions .72
Annex I (normative) Integral transforms .73
Annex J (normative) Restoration filters . .84
Annex K (normative) Image features .87
Annex L (normative) Colour transforms .92
Annex M (informative) Encoder overview .98
Bibliography . 101
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© ISO/IEC 2022 – All rights reserved

Foreword
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Commission) form the specialized system for worldwide standardization. National bodies that are
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are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria
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accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives or
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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.
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
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