ISO/IEC 21122-5:2022

Information technology — JPEG XS low-latency lightweight image coding system — Part 5: Reference software

This document contains the reference software of the ISO/IEC 21122 series. It acts as a guideline for implementation and as a reference for conformance testing.

Technologies de l'information — Système de codage d’images léger à faible latence JPEG XS — Partie 5: Logiciel de référence

General Information

• Status: Published
• Publication Date: 26-Sep-2022
• ICS: 35.040.30 - Coding of graphical and photographical information
• Technical Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Drafting Committee: ISO/IEC JTC 1/SC 29/WG 1 - JPEG Coding of digital representations of images
• Current Stage: 6060 - International Standard published
• Due Date: 02-Feb-2024
• Completion Date: 27-Sep-2022

RELATIONS

• Replaces: ISO/IEC 21122-5:2020 - Information technology — JPEG XS low-latency lightweight image coding system — Part 5: Reference software
• Effective Date: 26-Nov-2021

Standards Content (sample)

INTERNATIONAL ISO/IEC
STANDARD 21122-5
Second edition
2022-09
Information technology — JPEG XS
low-latency lightweight image coding
system —
Part 5:
Reference software
Technologies de l'information — Système de codage d’images léger à
faible latence JPEG XS —
Partie 5: Logiciel de référence
Reference number
ISO/IEC 21122-5:2022(E)
© ISO/IEC 2022
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ISO/IEC 21122-5:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2022

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

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO/IEC 2022 – All rights reserved
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ISO/IEC 21122-5:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Reference software ........................................................................................................................................................................................... 1

4.1 General ........................................................................................................................................................................................................... 1

4.2 Purpose ......................................................................................................................................................................................................... 1

4.3 Examples of use ..................................................................................................................................................................................... 2

5 Copyright, licensing and intellectual property ................................................................................................................... 2

Annex A (informative) Building the reference software ................................................................................................................ 3

Annex B (informative) Image file formats read and written by the reference software.............................4

Annex C (informative) Using the reference software ........................................................................................................................ 8

Bibliography .............................................................................................................................................................................................................................13

iii
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ISO/IEC 21122-5:2022(E)
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

www.iec.ch/members_experts/refdocs).

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

of patent rights. ISO and IEC 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) or the IEC

list of patent declarations received (see https://patents.iec.ch).

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 www.iec.ch/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 21122-5:2020), which has been

technically revised.
The main changes are as follows:
— Updated reference software.

A list of all parts in the ISO/IEC 21122 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

www.iec.ch/national-committees.
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ISO/IEC 21122-5:2022(E)
Introduction

This document is part of a series of standards for a low-latency lightweight image coding system,

denoted JPEG XS.

It provides the software reference implementation of the ISO/IEC 21122-1 and ISO/IEC 21122-2

standards. It has been successfully compiled and tested on various operating systems at the time of

writing. It is important to note that this reference software implementation represents just one way of

implementing JPEG XS. This implementation can serve as a validation anchor to other implementations.

No guarantee of the quality that will be achieved by an encoder is provided by its conformance

to ISO/IEC 21122-1 and ISO/IEC 21122-2, as the conformance is only defined in terms of specific

constraints imposed on the syntax of the generated codestream. In particular, while sample encoder

software implementations may suffice to provide some illustrative examples of which quality can be

achieved within the ISO/IEC 21122 series, they provide neither an assurance of minimum guaranteed

image encoding quality nor maximum achievable image encoding quality.

Similarly, the computation resource characteristics in terms of program or data memory usage,

execution speed, etc. of sample software encoder or decoder implementations should not be construed

as a representative of the typical, minimal or maximal computational resource characteristics to be

exhibited by implementations of the ISO/IEC 21122 series.

The International Organization for Standardization (ISO) and the International Electrotechnical

Commission (IEC) draw attention to the fact that it is claimed that compliance with this document may

involve the use of a patent.

ISO and IEC take no position concerning the evidence, validity and scope of this patent right.

The holder of this patent right has assured ISO and IEC that he/she is willing to negotiate licences under

reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this

respect, the statement of the holder of this patent right is registered with ISO and IEC. Information may

be obtained from the patent database available at www.iso.org/patents or https://patents.iec.ch.

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

of patent rights other than those in the patent database. ISO and IEC shall not be held responsible for

identifying any or all such patent rights.
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INTERNATIONAL STANDARD ISO/IEC 21122-5:2022(E)
Information technology — JPEG XS low-latency lightweight
image coding system —
Part 5:
Reference software
1 Scope

This document contains the reference software of the ISO/IEC 21122 series. It acts as a guideline for

implementation and as a reference for conformance testing.
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 21122-1, Information technology — JPEG XS low-latency lightweight image coding system — Part

1: Core coding system

ISO/IEC 21122-2, Information technology — JPEG XS low-latency lightweight image coding system — Part

2: Profiles and buffer models
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/IEC 21122-1 and

ISO/IEC 21122-2 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/
4 Reference software
4.1 General

In addition to the main text, including Annexes A to C, the reference software is available at https://

standards .iso .org/ iso -iec/ 21122/ -5/ ed -2/ en/ .
4.2 Purpose
The purpose of this document is to provide the following:

— Provide a reference decoder software implementation, capable of decoding codestreams that

conform to ISO/IEC 21122-1, or to ISO/IEC 21122-1 and ISO/IEC 21122-2.

— Provide a sample encoder software implementation, capable of producing codestreams that conform

to ISO/IEC 21122-1, or to ISO/IEC 21122-1 and ISO/IEC 21122-2.
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ISO/IEC 21122-5:2022(E)

The use of this reference software is not required for making an implementation of an encoder or

decoder in conformance to any of the parts of the ISO/IEC 21122 series. Requirements established in

ISO/IEC 21122-1 and ISO/IEC 21122-2 take precedence over the behaviour of the reference software.

The reference decoder software generates the normative output of the decoding process specified

by ISO/IEC 21122-1. The output of the reference decoder satisfies the requirements of the strict

conformance point of ISO/IEC 21122-4. It therefore allows conformance testing by means of comparing

the output of a candidate implementation by that of the reference software specified in this document.

Conformance testing is specified in ISO/IEC 21122-4. The reference decoder software can also be used

to validate the syntactic correctness of a codestream by attempting to decode a candidate codestream

with the reference software.
4.3 Examples of use

Some examples of use for the reference decoder software implementations are as follows:

— As an illustration of how to perform the decoding processes specified in ISO/IEC 21122-1.

— As the starting basis for the implementation of a decoder that conforms to ISO/IEC 21122-1.

— For testing the conformance of a decoder implementation to ISO/IEC 21122-1 with the procedures

specified in ISO/IEC 21122-4. Details on reference testing can be found in ISO/IEC 21122-4.

— For (non-exhaustive) testing of the conformance of a codestream (or file) to the constraints specified

in ISO/IEC 21122-1.

The lack of detection of any conformance violation by any reference software implementation should

not be considered as a definite proof that the codestream under testing conforms to all constraints

required for it be conforming to ISO/IEC 21122-1 or ISO/IEC 21122-2. In fact, ISO/IEC 21122-4 defines

additional testing procedures that can be used to test a codestream for conformance to ISO/IEC 21122-1

and ISO/IEC 21122-2, such as for example testing the conformance to the buffer models specified there.

Some examples of use for a sample encoder software are as follows:

— As an illustration of how to implement an encoding process that produces codestreams that are

conforming to ISO/IEC 21122-1 and ISO/IEC 21122-2.

— As starting point for an implementation of an encoder that conforms to ISO/IEC 21122-1 and

ISO/IEC 21122-2.

— As a means of generating codestreams conforming to ISO/IEC 21122-1 and ISO/IEC 21122-2 for

testing purposes.

— As a means of demonstrating and evaluating examples of the quality that can be achieved by an

encoding process that conforms to ISO/IEC 21122-1 and ISO/IEC 21122-2.

It is not recommended to use the reference software in a production environment, as it lacks proper

protection mechanisms against memory corruption and code execution exploits.
5 Copyright, licensing and intellectual property

The reference software was originally developed by the parties indicated in the file LICENCE.md within

the package forming a part of this document, in the course of development of ISO/IEC 21122-5. ISO/

IEC draws the attention of the users of this software to the license terms and conditions specified in the

same LICENSE.md file.
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ISO/IEC 21122-5:2022(E)
Annex A
(informative)
Building the reference software
A.1 Unpacking the software

The reference software is provided in the form of a ZIP archive named xs_ref_sw_ed2.zip. Unpacking

the archive is operating system specific, but on most POSIX compliant operating systems this can be

done by opening a command line terminal and issuing the following:
unzip xs_ref_sw_ed2.zip
This will unpack all files in the archive into the current directory.
A.2 Building the software

The source code is written in C11 and is designed to run on most modern operating systems. The exact

tools and versions depend on the operating system and the compiler to be used. A README.md file is

included with the software describing the steps to build the software.
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ISO/IEC 21122-5:2022(E)
Annex B
(informative)
Image file formats read and written by the reference software
B.1 General

The reference software supports a wide variety of image file formats, used as input for the encoder and

as output for the decoder, that are well established and easy to use, understand, and implement. This

annex describes the three most important image file formats.
B.2 PGX
B.2.1 General

This clause describes the PGX image file format, supported by the reference software and used by

ISO/IEC 21122-4 for the decoded reference images. This file format is capable of representing any input

or output image that is supported by JPEG XS (1 or more components and 1 to 16 bits per component

value).

The format consists of a directory file, one header file per component, and one raw data file per

component.

NOTE The difftest_ng tool (see ISO/IEC 21122-4) can convert between PGX and many other image file

formats.
B.2.2 Directory file

The directory file is the file that is provided as input file to the comparison tool (PGX file extension). It

consists, for each component, of the file name of the raw data file encoded in ASCII (see Reference [1]),

relative to the path where the directory file is located. Each raw data file name is terminated by a single

line feed character (ASCII 10=0x0a).

NOTE The PGX directory file does not separate lines by CR/LF pairs, i.e. the ASCII 13=0x0d, 10=0x0a code

sequence.
B.2.3 Header file

The header file is derived from the file name of the raw data file listed in the directory file by removing

the postfix .raw and replacing it by the postfix .h. It describes the format in which the raw format is

encoded. There is one separate header file per component.

Each header file consists of a single line, terminated by a single Line Feed character (ASCII 10=0x0a)

describing the format. It consists of the following fields, where angle brackets < > indicate parameters

described below and SPC indicates a blank space (ASCII 32=0x20):
PSPCSPCSPCSPC
where:

identifies the header file and shall be present. It has no particular meaning beyond

format identification.
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ISO/IEC 21122-5:2022(E)

identifies the sample format. ISO/IEC 21122 stores integer samples only, which are

indicated by the single character G as dataformat.

identifies the endianness of the encoded data. The characte
...