ISO/IEC DIS 18181-2

Information technology -- JPEG XL Image coding system

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DRAFT INTERNATIONAL STANDARD
ISO/IEC DIS 18181-2
ISO/IEC JTC 1/SC 29 Secretariat: JISC
Voting begins on: Voting terminates on:
2020-10-20 2021-01-12
Information technology — JPEG XL Image coding system —
Part 2:
File format
ICS: 35.040.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
This document is circulated as received from the committee secretariat.
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/IEC DIS 18181-2:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO/IEC 2020
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ISO/IEC DIS 18181-2:2020(E)
ISO 18181-2:2020(X)
Contents
Scope 5
Normative references 5
Terms and definitions 5
General 7
File organization 7
Data types and numerical values 9
Graphical descriptions (informative) 10
Binary format of a box 10
Box Types 11
9.1 JPEG XL Signature box 11
9.2 File Type box 11
9.3 JUMBF box 11
9.4 Exif box 12
9.5 XML box 12
9.6 Compressed XML box 12
9.7 Frame Index box 12
9.8 JPEG XL Codestream box 14
9.9 JPEG XL Partial Codestream box 14
Annex A 14
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Website: www.iso.org
© ISO 2020 – All rights reserved 3
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved
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ISO/IEC DIS 18181-2:2020(E)
Contents
Scope 5
Normative references 5
Terms and definitions 5
General 7
File organization 7
Data types and numerical values 9
Graphical descriptions (informative) 10
Binary format of a box 10
Box Types 11
9.1 JPEG XL Signature box 11
9.2 File Type box 11
9.3 JUMBF box 11
9.4 Exif box 12
9.5 XML box 12
9.6 Compressed XML box 12
9.7 Frame Index box 12
9.8 JPEG XL Codestream box 14
9.9 JPEG XL Partial Codestream box 14
Annex A 14
© ISO/IEC 2020 – All rights reserved 3
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ISO/IEC DIS 18181-2:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national

standards bodies (ISO member bodies). The work of preparing International Standards is

normally carried out through ISO technical committees. Each member body interested in a

subject for which a technical committee has been established has the right to be represented on

that committee. International organizations, governmental and non-governmental, in liaison

with ISO, also take part in the work. ISO collaborates closely with the International

Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

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 ISO documents 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​).

Attention is drawn to the possibility that some of the elements of this document may be the

subject of patent rights. ISO shall not be held responsible for identifying any or all such patent

rights. Details of any patent rights identified during the development of the document will be in

the Introduction and/or on the ISO list of patent declarations received (see
www.iso.org/patents​).

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​.

This document was prepared by 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 18181 series can be found on the ISO website.

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​.

4 © ISO/IEC 2020 – All rights reserved
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ISO/IEC DIS 18181-2:2020(E)
Introduction

This document is part of a series of standards denoted JPEG XL. This document describes JPEG

XL Part 2 (ISO/IEC 18181-2), the Transport and Container formats for JPEG XL codestreams as

specified in ISO/IEC 18181-1. This provides a way to add metadata and extensions to JPEG XL

codestreams. A file as described by this document is called a JPEG XL file.
Information Technology — JPEG XL Image Coding System —
Part 2: File format
1 Scope

This document is part of a series of standards denoted JPEG XL. This document describes JPEG

XL Part 2 (ISO/IEC 18181-2), the Transport and Container formats for JPEG XL codestreams as

specified in ISO/IEC 18181-1. This provides a way to add metadata and extensions to JPEG XL

codestreams. A file as described by this document is called a JPEG XL file.
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/IEC 18181-1, ​Information technology — JPEG XL Image Coding System — Part 1: Core coding

system

ISO/IEC 19566-5, ​Information technologies — JPEG systems — Part 5: JPEG universal metadata

box format (JUMBF)

ISO/IEC 21122-3, ​Information technology — JPEG XS low-latency lightweight image coding

system — Part 3: Transport and container formats

ISO/IEC 15444-2, Information technology — JPEG 2000 image coding system: Extensions — Part

ISO/IEC 23008-12, ​Information technology — High efficiency coding and media delivery in

heterogeneous environments — Part 12: Image File Format
INTERNET ENGINEERING TASK FORCE (IETF). RFC 7932: ​Brotli Compressed Data Format

[online]. Edited by J. Alakuijala and Z. Szabadka. July 2016 [viewed 2020-04-29]. Available at

https://tools.ietf.org/html/rfc7932
3 Terms and definitions

For the purposes of this document, the terms and definitions given in JPEG XL Part 1 (ISO/IEC

18181-1), ISO/IEC 19566-5 and the following apply.
© ISO/IEC 2020 – All rights reserved 5
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ISO/IEC DIS 18181-2:2020(E)
3.1
box
structured collection of data describing the image or the image decoding process
3.2
box content
data wrapped within the box structure
3.3
box type
kind of information stored within the box
3.4
byte
8 consecutive bits encoding a value between 0 and 255
3.5
codestream
JPEG XL codestream as specified in ISO/IEC 18181-1
3.6
file format

set of data structures for the storage of metadata and extensions of a codestream as defined by

this document
3.7
JPEG XL file
data file encoded in the file format defined by this document
3.8
superbox
box that carries other boxes as payload data
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ISO/IEC DIS 18181-2:2020(E)
4 General
This document defines the file format of a JPEG XL file.

A JPEG XL file shall contain a codestream as specified in ISO/IEC 18181-1, and may contain

additional metadata and extensions.
A JPEG XL file shall come in one of the following forms:
● A box structure, as defined in Clause 5.
● A direct JPEG XL codestream without box structure

The rest of this document only defines the box structure, the codestream without box structure

is valid but is completely specified in ISO/IEC 18181-1.

A decoder shall require the file format to follow either the structure of a codestream without

box structure, or follow the box structure as defined in Clause 5 and follow all box requirements

in the succeeding Clauses. A decoder can extract the codestream from the box structure and

decode the image from the codestream using the procedure specified in ISO/IEC 18181-1, and

can decode the contents of other boxes following their respective specifications in this

document.

INFORMATIVE NOTE A direct JPEG XL codestream without box structure is also a valid JPEG XL

file. This allows, for example, a more efficient encoding of images for the web, in cases where

information encoded in other boxes than the codestream is not required.
5 File​ ​organization

A JPEG XL file using the box structure is formed as a series of boxes. These boxes contain all data

within the file, including the initial signature required by the file format. This box-based file

format is based on the same syntax as described in the specification ISO/IEC 15444-1, Annex I

or ISO/IEC 15444-2, Annex M. The binary format of a box is also described in subclause A.2 of

this document. Boxes of different types contain different types of data, such as the file signature,

metadata, and the codestream. Further clauses in this document define box types that may

appear in a JPEG XL file and their requirements. Boxes with an unrecognized type shall be

ignored and skipped by the decoder.

A JPEG XL file shall contain a JPEG XL codestream. The codestream can be split across multiple

boxes: JPEG XL partial codestream boxes. In this case, the codestream is formed by the

concatenation of the content of all those boxes.
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ISO/IEC DIS 18181-2:2020(E)

Any boxes, content and codestreams present in a superbox, such as another JPEG XL file in a

JUMBF superbox, shall not be taken into account for the syntactic requirements of this

document; they recursively follow their applicable specification.

Figures 5.1 and 5.2 each show a conceptual box structure of a JPEG XL file, that is a possible

series of different box types that form the file, respectively with a single full codestream box and

with multiple partial codestream boxes. Boxes that may appear multiple times are indicated

with '...' and optional boxes are indicated in a dashed rectangle. These figures are only an

indication and do not imply any ordering or counting requirements for the boxes.
JPEG XL File
JPEG XL Signature box
File Type box
JPEG XL Frame Index box
JPEG XL Codestream box
JUMBF box ...
Exif box
XML box ...
Compressed XML box ...
Figure 5.1 — Conceptual structure of a JPEG XL file using a full codestream box
8 © ISO/IEC 2020 – All rights reserved
...