ISO/IEC 18181-2:2024
(Main)Information technology — JPEG XL image coding system — Part 2: File format
Information technology — JPEG XL image coding system — Part 2: File format
This document specifies the transport and container formats for JPEG XL codestreams as specified in ISO/IEC 18181-1. This document specifies how to add metadata and extensions to JPEG XL codestreams. A file as described by this document is called a JPEG XL file.
Technologies de l'information - Systѐme de codage d'images JPEG XL — Partie 2: Format de fichiers
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Standards Content (Sample)
International
Standard
ISO/IEC 18181-2
Second edition
Information technology — JPEG XL
2024-06
image coding system —
Part 2:
File format
Technologies de l'information - Systѐme de codage d'images
JPEG XL —
Partie 2: Format de fichiers
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 . 1
4 General . 2
5 File organization . 2
6 Data types and numerical values . 3
7 Graphical descriptions . 3
8 Binary format of a box . . 4
9 Box types . 4
9.1 JPEG XL Signature box .4
9.2 File Type box .5
9.3 Level box .5
9.4 JUMBF box .5
9.5 Exif box .5
9.6 XML box .6
9.7 Brotli-compressed box .6
9.8 Frame Index box .6
9.9 JPEG XL Codestream box .7
9.10 JPEG XL Partial Codestream box .7
9.11 JPEG Bitstream Reconstruction Data box .8
Annex A (normative) JPEG Bitstream Reconstruction procedure .11
Annex B (normative) JPEG XL Media Type registration .15
Bibliography . 17
© ISO/IEC 2024 – All rights reserved
iii
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).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). ISO and IEC take 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 and IEC had not
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 and https://patents.iec.ch. ISO and IEC 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.
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 18181-2:2021), which has been technically
revised.
The main changes are as follows:
— Cross-references to ISO/IEC 18181-1 are updated to match its second edition;
— The JPEG bitstream reconstruction procedure was moved to Annex A and revised to improve clarity;
— Annex B was added, specifying the image/jxl media type registration.
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
www.iec.ch/national-committees.
© ISO/IEC 2024 – All rights reserved
iv
International Standard ISO/IEC 18181-2:2024(en)
Information technology — JPEG XL image coding system —
Part 2:
File format
1 Scope
This document specifies the transport and container formats for JPEG XL codestreams as specified in
ISO/IEC 18181-1. This document specifies how 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 18181-1:2024, Information technology — JPEG XL Image Coding System — Part 1: Core coding system
ISO/IEC 10918-1:1994, Information technology — Digital compression and coding of continuous-tone still
images: Requirements and guidelines
ISO/IEC 19566-5, Information technologies — JPEG systems — Part 5: JPEG universal metadata box format (JUMBF)
1)
IETF RFC 7932, Brotli Compressed Data Format
3 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
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
file format
set of data structures for the storage of metadata and extensions of a codestream
1) https:// www .rfc -editor .org/ info/ rfc7932
© ISO/IEC 2024 – All rights reserved
3.5
JPEG XL file
data file encoded in the file format defined by this document
3.6
superbox
box that carries other boxes as payload data
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 Clauses 6 to 9. 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.
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.
The JPEG XL media type registration for image/jxl is specified in Annex B.
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.
NOTE This box-based file format is based on the same syntax as described in ISO/IEC 15444-1:2019, Annex I or
ISO/IEC 15444-2:2021, Annex M, or ISO/IEC 21122-3. The binary format of a box is also described in Clause 8.
Boxes of different types contain different types of data, such as the file signature, metadata and the
codestream. Clause 9 defines 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.
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.
Tables 1 and 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 ‘…’, optional boxes are indicated with
brackets and required boxes are indicated in bold. These figures are only an indication and do not imply
© ISO/IEC 2024 – All rights reserved
any ordering or counting requirements for the boxes. The decoder shall not make any assumptions about the
ordering of any boxes after the first two, except where ind
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