ISO/IEC 21122-2:2022
(Main)Information technology — JPEG XS low-latency lightweight image coding system — Part 2: Profiles and buffer models
Information technology — JPEG XS low-latency lightweight image coding system — Part 2: Profiles and buffer models
This document defines a number of subsets of the syntax specified in ISO/IEC 21122-1 as profiles. It also defines lower bounds on the throughput in the decoded domain via levels and the encoded domain via sublevels that a conforming decoder implementation shall support. Furthermore, it defines a buffer model to ensure interoperability between implementations in the presence of a latency constraint.
Technologies de l'information — Système de codage d'images léger à faible latence JPEG XS — Partie 2: Profils et modèles tampons
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INTERNATIONAL ISO/IEC
STANDARD 21122-2
Second edition
2022-03
Information technology — JPEG XS
low-latency lightweight image coding
system —
Part 2:
Profiles and buffer models
Technologies de l'information — Système de codage d'images léger à
faible latence JPEG XS —
Partie 2: Profils et modèles tampons
Reference number
© ISO/IEC 2022
© ISO/IEC 2022
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© ISO/IEC 2022 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 4
3.3 Symbols . 4
4 Conventions . 6
4.1 Conformance language . 6
4.2 Operators . 6
4.2.1 Arithmetic operators . 6
4.2.2 Logical operators . 6
4.2.3 Relational operators . 6
4.2.4 Precedence order of operators . 6
4.2.5 Mathematical functions . 7
5 Buffer model . 7
5.1 General system block diagram . 7
5.2 Influencing variables on the required buffer sizes . 8
5.3 Role of the buffer model . 9
6 Interpretation of Bayer data . 9
Annex A (normative) Profiles, levels and sublevels .11
Annex B (normative) Packet-based JPEG XS decoder model .25
Annex C (normative) Packet-based constant bit rate buffer model .31
Annex D (informative) Encoder model, latency bounds and codestream conformance
properties for the packet-based constant bit rate buffer model .37
Annex E (informative) JPEG XS latency analysis .42
Bibliography .49
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© ISO/IEC 2022 – All rights reserved
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 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 21122-2:2019), which has been
technically revised.
The main changes are as follows:
— addition of new profiles to compress colour filter array images (CFA images), to allow mathematically
lossless image compression, and to compress 4:2:0 colour sampled images.
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 2022 – All rights reserved
Introduction
This document is part of a series of standards for a low-latency lightweight image coding system,
denoted as JPEG XS.
While ISO/IEC 21122-1 specifies a full set of compression coding tools needed to satisfy all of the
requirements of JPEG XS, a targeted application can often work with a simpler and reduced set
of coding tools, and with or without tighter constraints, to meet its targeted goals. For this reason,
profiles, levels, and sublevels are defined in this document. These three concepts facilitate partial and
reduced complexity implementations of ISO/IEC 21122-1 for such specific application use cases, while
also safeguarding interoperability.
This document specifies a limited number of profiles to represent interoperability subsets of the
codestream syntax specified in ISO/IEC 21122-1 with each profile serving specific application use
cases. In other word, profiles select a subset of the available coding tools. In addition, levels and
sublevels provide limits to the maximum throughput in respectively the encoded (codestream) and the
decoded (spatial/pixel) domains. In this way, profiles, levels and sublevels allow designing cost-efficient
implementations that serve the needs of the desired applications.
In addition to being light-weight, another major requirement of JPEG XS is to allow low end-to-end
latency, limited to a fraction of the frame size. To ensure this low-latency property, this document
also specifies a buffer model, consisting of a decoder model and a transmission channel model. The
models show the interaction of a hypothetical reference decoder, including its smoothing buffer with a
constant bitrate channel feeding this buffer. The size of the decoder smoothing buffer is computed from
the profile, level, and sublevel. Codestreams are formed such that the buffer of a decoder, operating
according to this buffer model, never overflows or underflows. In effect, the buffer model provides
encoders with the necessary information to generate codestreams that can be decoded by an arbitrary
decoder implementation, ensuring system interoperability.
In addition to the size of the decoder smoothing buffer, end-to-end latency also depends on the latency
inherent to each processing step of the encoding-decoding chain whose methods are described in
ISO/IEC 21122-1. To help implementers estimate the latency of their device, this document gives extra
information on the minimum latency that can be achieved by the different methods described in
ISO/IEC 21122-1.
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© ISO/IEC 2022 – All rights reserved
INTERNATIONAL STANDARD ISO/IEC 21122-2:2022(E)
Information technology — JPEG XS low-latency lightweight
image coding system —
Part 2:
Profiles and buffer models
1 Scope
This document defines a number of subsets of the syntax specified in ISO/IEC 21122-1 as profiles. It
also defines lower bounds on the throughput in the decoded domain via levels and the encoded domain
via sublevels that a conforming decoder implementation shall support. Furthermore, it defines a buffer
model to ensure interoperability between implementations in the presence of a latency constraint.
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, JPEG XS low-latency lightweight image coding system — Part 1: Core coding system
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 21122-1 and the following
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
blanking codestream fragment
placeholder codestream fragment representing blanking periods
3.1.2
buffer model
combination of a decoder model and a channel model whose behaviour can be defined by a set of
parameters
3.1.3
buffer model instance
specific configuration of a buffer model specified by the assignment of well-defined values to the buffer
model parameters
3.1.4
channel model
model describing the temporal behaviour of the transmission channel connecting an encoder and a
decoder
© ISO/IEC 2022 – All rights reserved
3.1.5
coded codestream fragment
continuous sequence of bits in the codestream containing exactly one packet body and a well-defined
number of packet headers, markers and marker segments
3.1.6
codestream fragment
either coded codestream fragment, or blanking codestream fragment
3.1.7
cycle
single clock period of an encoder or decoder clocked implementation
3.1.8
decoder model
combination of a decoder unit and a decoder smoothing buffer
3.1.9
decoder smoothing buffer
memory buffer that is used to level out changes in the number of bits read by a decoder unit per time
unit
3.1.10
decoder unit
module reading a variable number of bits per time unit to generate decoded output pixels with a fixed
rate
3.1.11
decompositio
...
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