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International
Standard
ISO/IEC 21122-1
Third edition
Information technology — JPEG
2024-07
XS low-latency lightweight image
coding system —
Part 1:
Core coding system
Technologies de l'information — Système de codage d'images
léger à faible latence JPEG XS —
Partie 1: Système de codage de noyau
Reference number
© ISO/IEC 2024
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© ISO/IEC 2024 – All rights reserved
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions, abbreviated terms and symbols . 1
3.1 Terms and definitions .1
3.2 Abbreviated terms .6
3.3 Symbols .6
4 Conventions . 10
4.1 Conformance language .10
4.2 Operators .10
4.2.1 Arithmetic operators .10
4.2.2 Logical operators .10
4.2.3 Relational operators .10
4.2.4 Precedence order of operators .10
4.2.5 Mathematical functions .11
5 Functional concepts . .11
5.1 Sample grid, sampling and components .11
5.2 Interpretation of CFA data . 12
5.3 Wavelet decomposition . 12
5.4 Codestream. 13
6 Encoder requirements .13
7 Decoder .13
7.1 Decoding process general provisions . 13
7.2 Decoder requirements . 15
Annex A (normative) Codestream syntax .16
Annex B (normative) Image data structures .32
Annex C (normative) Entropy decoding .45
Annex D (normative) Quantization .65
Annex E (normative) Discrete wavelet transformation .70
Annex F (normative) Multiple component transformations .80
Annex G (normative) DC level shifting, non-linear transform and output clipping.91
Annex H (normative) Frame buffer . .98
Annex I (informative) Example weight tables .106
Bibliography .114
© ISO/IEC 2024 – All rights reserved
iii
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 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes 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 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. ISO 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.
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 third edition cancels and replaces the second edition (ISO/IEC 21122-1:2022), which has been
technically revised.
The main changes are as follows:
— coding tools for improving the compression rates for screen content images have been added;
— coding tools that enable lossless coding of images with up to 16 bits per sample have been added.
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
/national-committees.
© ISO/IEC 2024 – All rights reserved
iv
International Standard ISO/IEC 21122-1:2024(en)
Information technology — JPEG XS low-latency lightweight
image coding system —
Part 1:
Core coding system
1 Scope
This document specifies the syntax and an accompanying decompression process that is capable to represent
continuous-tone grey-scale, or continuous-tone colour digital images without visual loss at moderate
compression rates. Typical compression rates are between 2:1 and 18:1 but can also be higher depending
on the nature of the image. In particular, the syntax and the decoding process specified in this document
allow lightweight encoder and decoder implementations that limit the end-to-end latency to a fraction of the
frame size. However, the definition of transmission channel buffer models necessary to ensure such latency
is beyond the scope of this document.
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
There are no normative references in this document.
3 Terms and definitions, abbreviated terms and symbols
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/
3.1.1
band
input data to a specific wavelet filter type (3.1.54) that contributes to the generation of one of the components
(3.1.14) of the image
3.1.2
band type
single number collapsing the information on the component, and horizontal and vertical wavelet filter types
that are applied in the filter cascade reconstructing spatial image samples from inversely quantized wavelet
coefficients
© ISO/IEC 2024 – All rights reserved
3.1.3
bit
binary choice encoded as either 0 or 1
3.1.4
bitplane
array of bits having all the same significance
3.1.5
bitplane count
number of significant bitplanes of a code group, counting from the LSB up to the most significant, non-empty
bitplane
3.1.6
bitplane count subpacket
subset of a packet which decodes to the bitplane counts of all code groups within a packet, followed by
padding and optional filler bytes
Note 1 to entry: See subclause C.5.3.
3.1.7
byte
group of 8 bits
3.1.8
colour filter array
CFA
rectangular array of sensor elements yielding a 1-component image where the colour to which a sensor
element is sensitive to depends on the position of the sensor element
3.1.9
codestream
compressed image data representation that includes all necessary data to allow a (full or approximate)
reconstruction of the sample values of a digital image
3.1.10
code group
group of quantization indices in sign-magnitude representation before inverse quantization
3.1.11
coefficient
input value to the inverse wavelet transformation resulting from inverse quantization
3.1.12
coefficient group
number of horizontally adjacent wavelet coefficients from the same band
3.1.13
column
set of vertically aligned precincts
3.1.14
component
two-dimensional array of samples having the same designation such as red, green or blue in the output or
display device
3.1.15
compression
process of reducing the number of bits used to represent source image data
© ISO/IEC 2024 – All rights reserved
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