ISO/IEC 10918-4:2024

Information technology - Digital compression and coding of continuous-tone still images - Part 4: APPn markers

This document provides definitions for JPEG application specific markers found in Rec. ITU‑T T.81 | ISO/IEC 10918-1 and Rec. ITU-T T.84 | ISO/IEC 10918-3.

Technologies de l'information — Compression numérique et codage des images fixes à modelé continu — Partie 4: Marqueurs APPn

General Information

• Status: Published
• Publication Date: 16-May-2024
• 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 - Coding of audio, picture, multimedia and hypermedia information
• Current Stage: 6060 - International Standard published
• Start Date: 17-May-2024
• Due Date: 02-Mar-2024
• Completion Date: 17-May-2024

Relations

• Revises: ISO/IEC 10918-4:1999 - Information technology - Digital compression and coding of continuous-tone still images: Registration of JPEG profiles, SPIFF profiles, SPIFF tags, SPIFF colour spaces, APPn markers, SPIFF compression types and Registration Authorities (REGAUT) - Part 4:
• Effective Date: 24-Sep-2022
• Revises: ISO/IEC 10918-4:1999/Amd 1:2013 - Information technology - Digital compression and coding of continuous-tone still images: Registration of JPEG profiles, SPIFF profiles, SPIFF tags, SPIFF colour spaces, APPn markers, SPIFF compression types and Registration Authorities (REGAUT) - Part 4: - Amendment 1: Application specific marker list
• Effective Date: 24-Sep-2022

Overview

ISO/IEC 10918-4:2024 (ITU‑T Rec. T.86) defines the use and meaning of APPn (application‑specific) markers in JPEG codestreams. It provides precise definitions (including the notion of an identifier string) and publishes a consolidated list of reserved APPn marker/identifier pairs (Annex A). This second edition replaces ISO/IEC 10918-4:1999 (with Amendment 2013) and removes the original registration‑authority procedures. The document is intended to ensure predictable, interoperable handling of application metadata and extension markers in JPEG images.

Key topics and technical requirements

• Scope and references: Works together with Rec. ITU‑T T.81 | ISO/IEC 10918‑1 (JPEG requirements) and Rec. ITU‑T T.84 | ISO/IEC 10918‑3 (extensions).
• Identifier string: Defined as the first m bytes of APPn application data (zero‑terminated or multi‑glyph), used to disambiguate marker segments.
• Reserved APPn list (Annex A): Enumerates known marker/identifier pairs (e.g., APP0 JFIF/JFXX, APP1 EXIF/XMP, APP2 ICC_PROFILE/MPF, APP13 Photoshop IRB, APP14 Adobe, etc.). Many entries indicate multi‑segment usage where applicable.
• Parsing and interoperability guidance:
  • Applications should skip APPn segments they do not understand.
  • Implementations should preserve unknown APPn segments when updating images.
  • Use of APPn markers must not prevent codestream expansion if a marker is unrecognized, though functionality may be limited.
• Multi‑segment support: Several APPn usages (e.g., ICC_PROFILE, XMP, MPF) are explicitly multi‑segment and described in the annex.
• Normative cross‑references: Identifier encoding per ITU‑T T.50 or ISO/IEC 10646; related metadata standards cited (EXIF, XMP, ICC).

Applications and who uses it

ISO/IEC 10918-4 is essential for:

• JPEG codec and image‑processing software developers (parsing/preservation of metadata).
• Camera and imaging device manufacturers (embedding EXIF, MPF, maker notes).
• Color management and publishing vendors (ICC_PROFILE in APP2).
• Digital archivists, forensic analysts, and content‑management systems that need reliable handling of JPEG APPn metadata.
• Tool vendors implementing JFIF, XMP, MPF or Photoshop‑related markers.

Practical benefits include improved interoperability, predictable handling of metadata blocks (thumbnail, color profiles, multi‑picture containers), and reduced risk of marker collisions across implementations.

Related standards

• ISO/IEC 10918‑1 (Rec. ITU‑T T.81) - JPEG core format
• ISO/IEC 10918‑3 (Rec. ITU‑T T.84) - JPEG extensions / SPIFF
• ISO/IEC 10918‑5 (Rec. ITU‑T T.871) - JFIF
• ISO 15076‑1 - ICC_PROFILE
• ISO 16684‑1 - XMP
• CIPA DC‑010‑2020 - EXIF
• ISO/IEC 10646 - character encoding

Keywords: ISO/IEC 10918-4, JPEG APPn markers, APPn, JFIF, EXIF, XMP, ICC_PROFILE, JPEG metadata, image markers, Annex A reserved markers.

Standards Content (Sample)

International
Standard
ISO/IEC 10918-4
Second edition
Information technology — Digital
2024-05
compression and coding of
continuous-tone still images —
Part 4:
APPn markers
Technologies de l'information — Compression numérique et
codage des images fixes à modelé continu —
Partie 4: Marqueurs APPn
Reference number
© ISO/IEC 2024
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© ISO/IEC 2024 – All rights reserved
ii
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
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In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by ITU-T (as ITU-T Rec T.86) and drafted in accordance with its editorial rules,
in collaboration with 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 10918-4:1999), which has been technically
revised. It also incorporates the Amendment ISO/IEC 10918-4:1999/Amd 1:2013.
The main changes are as follows:
— cancels the provisions concerning the registration authority processes originally defined in the first
edition.
A list of all parts in the ISO/IEC 10918 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
iii
CONTENTS
Page
1 Scope . 1
2 Normative references . 1
2.1 Identical ITU-T Recommendations | International Standards . 1
3 Definitions . 1
4 Abbreviations and symbols . 1
5 Conventions . 1
6 General . 1
7 Purpose of an APPn marker . 2
Annex A – Application-specific marker list . 3
Bibliography . 4
© ISO/IEC 2024 – All rights reserved
Rec. ITU-T T.86 (V2) (02/2024)
iv
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information technology – Digital compression and coding of continuous-tone still images:
APPn markers
1 Scope
This Recommendation | International Standard provides definitions for JPEG application specific markers found in
Rec. ITU-T T.81 | ISO/IEC 10918-1 and Rec. ITU-T T.84 | ISO/IEC 10918-3.
2 Normative references
The following Recommendations and International Standards contain provisions which, through references in this text,
constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated
were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition
of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid
ITU-T Recommendations.
2.1 Identical ITU-T Recommendations | International Standards
– Recommendation ITU-T T.81 | ISO/IEC 10918-1, Information technology – Digital compression and
coding of continuous-tone still images: Requirements and guidelines.
– Recommendation ITU-T T.84 | ISO/IEC 10918-3, Information technology – Digital compression and
coding of continuous-tone still images: Extensions.
3 Definitions
The definitions used in Rec. ITU-T T.81 | ISO/IEC 10918-1, R
...