ISO 21496-1:2025
(Main)Digital photography — Gain map metadata for image conversion — Part 1: Dynamic range conversion
Digital photography — Gain map metadata for image conversion — Part 1: Dynamic range conversion
This document defines a gain map used in HDR digital photography applications, for dynamic range conversion between two image representations. This includes the definition of the gain map metadata and its attributes, how to specify the gain map and associated metadata, and how to apply the gain map using this metadata.
Photographie numérique — Carte de gain pour la conversion d’images — Partie 1: Conversion de plage de dynamique
General Information
Buy Standard
Standards Content (Sample)
International
Standard
ISO 21496-1
First edition
Digital photography — Gain map
2025-07
metadata for image conversion —
Part 1:
Dynamic range conversion
Photographie numérique — Carte de gain pour la conversion
d’images —
Partie 1: Conversion de plage de dynamique
Reference number
© ISO 2025
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, and acronyms . 1
4 Gain map requirements . 2
4.1 General .2
4.2 Gain map dimensions.3
4.3 Gain map colour components .3
4.4 Gain map quantization .3
4.5 Orientation .4
5 Metadata . 4
5.1 General .4
5.2 Gain map metadata .4
5.2.1 General .4
5.2.2 Dimensions .4
5.2.3 Quantization .4
5.2.4 Number of gain map components .4
5.2.5 Per-component metadata .4
5.2.6 Baseline high dynamic range headroom.5
5.2.7 Alternate HDR headroom .5
5.2.8 Version tag .5
5.3 Colorimetry metadata .5
5.3.1 General .5
5.3.2 Baseline image colorimetry metadata .5
5.3.3 Alternate image colorimetry metadata .6
5.3.4 Gain map application space colour primaries metadata .6
6 Gain map application . . 6
6.1 General .6
6.2 Processing the gain map .6
6.2.1 Unnormalizing the gain map .6
6.2.2 Resampling the gain map .7
6.3 Applying the gain map .7
Annex A (informative) Computing the gain map . 8
Annex B (normative) Colour conversion .10
Annex C (normative) Storing the gain map .11
Bibliography .15
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. 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 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 Technical Committee ISO/TC 42, Photography.
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.
iv
Introduction
High dynamic range (HDR) images, that have been produced for HDR displays, can provide a better user
experience. One challenge is ensuring that there is no image quality regression when displaying an HDR
image on a display with limited or no headroom, such as a standard dynamic range (SDR) display.
This can be solved by creating a standardized solution that includes storing in the same file a baseline image
and a gain map, to convert between the baseline and the alternate representations with different dynamic
ranges. Compared with storing both representations, the benefit of this solution is the optimization of the
file size, obtained by minimizing the amount of redundant data stored. It also avoids the logistical issues
caused by having separate files.
v
International Standard ISO 21496-1:2025(en)
Digital photography — Gain map metadata for image
conversion —
Part 1:
Dynamic range conversion
1 Scope
This document defines a gain map used in HDR digital photography applications, for dynamic range
conversion between two image representations.
This includes the definition of the gain map metadata and its attributes, how to specify the gain map and
associated metadata, and how to apply the gain map using this metadata.
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.
CIPA DC-007-Translation-2025 Multi-Picture Format
CIPA DC-008-Translation-2024 Exchangeable image file format for digital still cameras : Exif Version 3.0
ISO/IEC 10918-5, Information technology — Digital compression and coding of continuous-tone still images:
JPEG File Interchange Format (JFIF) — Part 5:
ISO/IEC 23091-2, Information technology — Coding-independent code points — Part 2: Video
3 Terms, definitions, and acronyms
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
alternate image
data structure that contains pixels and obtained by combining the baseline image and the gain map in the file
Note 1 to entry: The data is structured in accordance with the requirements of this document.
3.2
baseline image
data structure that contains pixels and image-related data, and is stored in the file as the main image
3.3
gain map
data structure that contains local quotients, and is used for conversion between two image representations,
the baseline image (3.2) and the alternate image (3.1)
3.4
gain map application space
linear RGB colour space in which the gain map (3.3) is applied
Note 1 to entry: This space is scaled such that the value of each of the 3 {R,G,B} colour components of the HDR reference
white is 1,0. Its colour primaries are either the colour primaries of the baseline image, or the colour primaries of the
alternate image (see 5.3.4 and B.2).
3.5
high dynamic range and wide colour gamut encoding
HDR/WCG encoding
colour image encoding that can contain wider variations in brightness, with a dynamic range significantly
...
FINAL DRAFT
International
Standard
ISO/FDIS 21496-1
ISO/TC 42
Digital photography — Gain map
Secretariat: ANSI
metadata for image conversion —
Voting begins on:
Part 1:
Dynamic range conversion
Voting terminates on:
Photographie numérique — Carte de gain pour la conversion
d’images —
Partie 1: Conversion de plage de dynamique
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 21496-1:2025(en) © ISO 2025
ISO/FDIS 21496-1:2025(en)
© ISO 2025
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO/FDIS 21496-1:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, and acronyms . 1
4 Gain map requirements . 2
4.1 General .2
4.2 Gain map dimensions.3
4.3 Gain map colour components .3
4.4 Gain map quantization .3
4.5 Orientation .4
5 Metadata . 4
5.1 General .4
5.2 Gain map metadata .4
5.2.1 General .4
5.2.2 Dimensions .4
5.2.3 Quantization .4
5.2.4 Number of gain map components .4
5.2.5 Per-component metadata .4
5.2.6 Baseline high dynamic range headroom.5
5.2.7 Alternate HDR headroom .5
5.2.8 Version tag .5
5.3 Colorimetry metadata .5
5.3.1 General .5
5.3.2 Baseline image colorimetry metadata .5
5.3.3 Alternate image colorimetry metadata .6
5.3.4 Gain map application space colour primaries metadata .6
6 Gain map application . . 6
6.1 General .6
6.2 Processing the gain map .6
6.2.1 Unnormalizing the gain map .6
6.2.2 Resampling the gain map .7
6.3 Applying the gain map .7
Annex A (informative) Computing the gain map . 8
Annex B (normative) Colour conversion .10
Annex C (normative) Storing the gain map .11
Bibliography .15
iii
ISO/FDIS 21496-1:2025(en)
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. 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 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 Technical Committee ISO/TC 42, Photography.
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.
iv
ISO/FDIS 21496-1:2025(en)
Introduction
High dynamic range (HDR) images, that have been produced for HDR displays, can provide a better user
experience. One challenge is ensuring that there is no image quality regression when displaying an HDR
image on a display with limited or no headroom, such as a standard dynamic range (SDR) display.
This can be solved by creating a standardized solution that includes storing in the same file a baseline image
and a gain map, to convert between the baseline and the alternate representations with different dynamic
ranges. Compared with storing both representations, the benefit of this solution is the optimization of the
file size, obtained by minimizing the amount of redundant data stored. It also avoids the logistical issues
caused by having separate files.
v
FINAL DRAFT International Standard ISO/FDIS 21496-1:2025(en)
Digital photography — Gain map metadata for image
conversion —
Part 1:
Dynamic range conversion
1 Scope
This document defines a gain map used in HDR digital photography applications, for dynamic range
conversion between two image representations.
This includes the definition of the gain map metadata and its attributes, how to specify the gain map and
associated metadata, and how to apply the gain map using this metadata.
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.
CIPA DC-007-Translation-2025 Multi-Picture Format
CIPA DC-008-Translation-2024 Exchangeable image file format for digital still cameras : Exif Version 3.0
ISO/IEC 10918-5, Information technology — Digital compression and coding of continuous-tone still images:
JPEG File Interchange Format (JFIF) — Part 5:
ISO/IEC 23091-2, Information technology — Coding-independent code points — Part 2: Video
3 Terms, definitions, and acronyms
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
alternate image
data structure that contains pixels and obtained by combining the baseline image and the gain map in the file
Note 1 to entry: The data is structured in accordance with the requirements of this document.
3.2
baseline image
data structure that contains pixels and image-related data, and is stored in the file as the main image
3.3
gain map
data structure that contains local quotients, and is used for conversion between two image representations,
the baseline image (3.2) and the alternate image (3.1)
...
Formatted: Left
Style Definition
ISO/FDIS 21496-1:2025(en) .
Formatted: Font: 14 pt, Bold, Font color: Auto, French
ISO /TC 42
(France)
Formatted: zzCover large
Secretariat: ANSI
Formatted: Right: 1.5 cm, Bottom: 1 cm, Gutter: 0 cm,
Date: 2025-05-03XX Section start: New page, Header distance from edge:
1.27 cm, Footer distance from edge: 1.27 cm
Formatted: French (France)
Formatted
...
Formatted: French (France)
Digital photography — Gain map metadata for image conversion
— —
Formatted: Regular, Font: Bold, French (France)
Part 1:
Formatted: Cover Title_A2, Adjust space between Latin
Dynamic range conversion
and Asian text, Adjust space between Asian text and
numbers
Photographie numérique — Carte de gain pour la conversion d’images —
Formatted
...
Partie 1: Conversion de plage de dynamique
FDIS stage
Formatted: Left
ISO/FDIS 21496-1:2025(en)
Formatted: Font: Bold
Formatted: HeaderCentered
Commented [eXtyles1]: The reference "ISO 2025" is to a
withdrawn standard
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
Formatted: Default Paragraph Font
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 Formatted: Default Paragraph Font
at the address below or ISO’s member body in the country of the requester.
Formatted: No page break before, Adjust space
between Latin and Asian text, Adjust space between
ISO copyright office
Asian text and numbers
CP 401 • Ch. de Blandonnet 8
Formatted: Adjust space between Latin and Asian text,
CH-1214 Vernier, Geneva
Adjust space between Asian text and numbers
Phone: + 41 22 749 01 11
EmailE-mail: copyright@iso.org
Formatted: French (France)
Website: www.iso.orgwww.iso.org
Formatted: French (France)
Published in Switzerland
Formatted: French (France)
Formatted: Font: 10 pt
Formatted: Font: 10 pt
Formatted: FooterPageRomanNumber, Space After: 0
pt, Line spacing: single
Formatted: Font: 11 pt
ii © ISO 2024 2025 – All rights reserved
ii
ISO/FDIS 21496-1:2025(en)
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Contents
Foreword . vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, and acronyms . 1
4 Gain map requirements . 3
4.1 General . 3
4.2 Gain map dimensions . 3
4.3 Gain map colour components . 4
4.4 Gain map quantization . 4
4.5 Orientation . 4
5 Metadata . 4
5.1 General . 4
5.2 Gain map metadata . 4
5.3 Colorimetry metadata . 6
6 Gain map application . 6
6.1 General . 6
6.2 Processing the gain map . 7
6.3 Applying the gain map . 7
Annex A (informative) Computing the gain map . 9
Annex B (normative) Colour conversion . 11
Annex C (normative) Storing the gain map . 12
Bibliography . 17
Foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, and acronyms . 6
3.1 alternate image . 6
3.2 baseline image . 6
3.3 gain map . 7
3.4 gain map application space . 7
3.5 high dynamic range and wide colour gamut encoding . 7
3.6 high dynamic range headroom . 7
Formatted: Font: 10 pt
3.7 high dynamic range image . 7
3.8 image . 7
Formatted: FooterCentered, Left, Space Before: 0 pt,
3.9 nominal peak luminance . 7
Tab stops: Not at 17.2 cm
3.10 reference diffuse white . 7
Formatted: Font: 10 pt
4 Gain map requirements . 8
Formatted: Font: 10 pt
4.1 General . 8
Formatted: Font: 11 pt
4.2 Gain map dimensions . 8
4.3 Gain map colour components . 8
Formatted: FooterPageRomanNumber, Left, Space
After: 0 pt, Tab stops: Not at 17.2 cm
© ISO 2025 – All rights reserved
iii
ISO/FDIS 21496-1:2025(en)
Formatted: Font: Bold
Formatted: HeaderCentered
4.4 Gain map quantization . 9
4.5 Orientation . 9
5 Metadata . 9
5.1 General . 9
5.2 Gain map metadata . 9
5.2.1 General . 9
5.2.2 Dimensions . 9
5.2.3 Quantization . 9
5.2.4 Number of gain map components. 9
5.2.5 Per-component metadata . 10
5.2.6 Baseline HDR headroom . 10
5.2.7 Alternate HDR headroom . 11
5.2.8 Version tag . 11
5.3 Colorimetry metadata . 11
5.3.1 General . 11
Baseline image colorimetry metadata . 11
5.3.2 11
Alternate image colorimetry metadata . 11
5.3.3 11
5.3.4 Gain map application space colour primaries metadata . 11
6 Gain map application . 11
6.1 General . 11
6.2 Processing the gain map . 12
6.2.1 Unnormalizing the gain map . 12
6.2.2 Resampling the gain map. 12
6.3 Applying the gain map . 12
Annex A (informative) Computing the gain map . 14
A.1 General . 14
A.2 Computing the gain map . 14
A.3 Processing the gain map . 14
A.3.1 General . 14
A.3.2 Resampling the gain map. 14
A.3.3 Normalizing the gain map . 15
A.3.4 Applying a gamma to the gain map . 15
Annex B (normative) Colour conversion . 16
B.1 General . 16
B.2 Colour primary conversions . 16
Annex C (normative) Storing the gain map .
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.