ISO 22028-5

Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 5: High dynamic range and wide colour gamut encoding for still images (HDR/WCG)

This document defines a set of colour image encodings for use in storage, transmission, and display of high dynamic range and wide colour gamut (HDR/WCG) digital still images. It defines the colour encodings, the mandatory and optional metadata, and the reference viewing conditions for HDR/WCG images.

Photographie et technologie graphique — Codages par couleurs étendues pour stockage, manipulation et échange d'image numérique — Partie 5: Plage dynamique élevée et codage large de la gamme de couleurs pour les images fixes (HDR/WCG)

General Information

• Status: Not Published
• ICS: 37.040.99 - Other standards related to photography
• ICS: 37.100.01 - Graphic technology in general
• Technical Committee: ISO/TC 42 - Photography
• Drafting Committee: ISO/TC 42/WG 23 - Joint ISO/TC 42 - ISO/TC 130 - CIE WG: Extended colour encodings for digital image storage, manipulation and interchange
• Current Stage: 6000 - International Standard under publication
• Start Date: 14-Apr-2026
• Completion Date: 18-Apr-2026

Relations

• Revises: ISO/TS 22028-5:2023 - Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 5: High dynamic range and wide colour gamut encoding for still images (HDR/WCG)
• Effective Date: 16-Sep-2023

Overview

ISO 22028-5:2026 defines standardized colour image encodings for high dynamic range (HDR) and wide colour gamut (WCG) digital still images. Developed by the International Organization for Standardization (ISO/TC42 Photography), this part of the ISO 22028 series specifies methods to encode, store, transmit, and display digital still images with expanded brightness and colour capabilities. It establishes both baseline and extended colour encoding options, along with required and optional metadata, ensuring consistent visual results across different imaging systems and devices.

With the expanding prevalence of HDR cameras, HDR/WCG displays (such as modern smartphones, televisions, and computer monitors), and enhanced consumer expectations for image fidelity, this standard supports the creation of high-quality, interoperable image content. It aims to unify image encoding formats for the digital still imaging industry, facilitating better colour reproduction, dynamic range, and compatibility with various display technologies.

Keywords: ISO 22028-5, HDR imaging, wide colour gamut, digital photography standards, image encoding, metadata for images, display compatibility

Key Topics

• HDR/WCG Colour Encoding:
  Provides specifications for baseline and extended encodings, referencing ITU-R BT.2100-3 for compatibility with global video and movie ecosystems. Supports both industry-standard signal formats and colour gamuts (such as P3-D65).

• Transfer Functions:
  Includes hybrid log-gamma (HLG) and perceptual quantization (PQ) encoding techniques for mapping and reconstructing scene and display-referred image data for HDR/WCG content.

• Reference Display and Viewing Conditions:
  Defines reference display primaries (P3-D65), nominal peak luminance (1000 cd/m²), black point luminance, HDR reference white, and controlled viewing conditions to ensure uniformity in image appearance.

• Comprehensive Metadata:
  Specifies mandatory and optional metadata, such as Coding-Independent Code Points (CICP), mastering display colour volume (MDCV), content colour volume (CCV), content light level (CLL), HDR reference white luminance, and scene-referred indicators for image states.

• Colour Mapping and Conversion:
  Recommends algorithms and workflows for colour space conversions and gamut mapping, ensuring optimal viewing experiences on displays with various capabilities-including tone mapping strategies from HDR to SDR outputs.

Applications

ISO 22028-5 enables robust, long-term, and interoperable support for HDR/WCG still image workflows in several practical contexts:

• Digital Photography and Image Editing:
  Standardizes how HDR/WCG images are captured, processed, and exchanged between cameras, editing software, and archival systems, enabling better preservation and rendering of detail in highlights and shadows.

• Professional and Consumer Imaging Devices:
  Ensures manufacturers of cameras, monitors, televisions, and other display equipment can implement a consistent level of colour accuracy and dynamic range, irrespective of hardware differences.

• Content Distribution and Archiving:
  Facilitates consistent results in the storage and transmission of image files with enhanced dynamic ranges, supporting integration with multimedia file formats and metadata frameworks.

• Media Production Ecosystems:
  Harmonizes with existing standards used in HDR/WCG television, film, and broadcast production, allowing seamless interchange between still images and video workflows.

• Colour Management and Printing:
  Helps colour management systems and digital printers accurately interpret HDR/WCG images, maintaining intended visual quality across different technologies.

Related Standards

• ISO 22028-1: Photography and graphic technology - Extended colour encodings for digital image storage, manipulation and interchange - Part 1: Architecture and requirements.
• ITU-R BT.2100-3: Image parameter values for high dynamic range television for use in production and international programme exchange.
• ISO/IEC 23091-2, 23091-4: Coding-independent code points - Video signal type identification and usage.
• ISO/IEC 23000-22 (MIAF): Media file format specification supporting HDR/WCG metadata.
• SMPTE ST 2113: Colorimetry of P3 Color Spaces.
• SMPTE ST 2086: Metadata for mastering display colour volume.

By adopting ISO 22028-5, organizations and creators across the imaging industry can ensure future-proof compatibility, optimal visual results, and a stronger HDR/WCG image ecosystem.

Standards Content (Sample)

DRAFT
International
Standard
ISO/DIS 22028-5
ISO/TC 42
Photography and graphic
Secretariat: ANSI
technology — Extended colour
Voting begins on:
encodings for digital image storage,
2025-10-14
manipulation and interchange —
Voting terminates on:
2026-01-06
Part 5:
High dynamic range and wide
colour gamut encoding for still
images (HDR/WCG)
Photographie et technologie graphique — Codages par couleurs
étendues pour stockage, manipulation et échange d'image
numérique —
Partie 5: Plage dynamique élevée et codage large de la gamme de
couleurs pour les images fixes (HDR/WCG)
ICS: 37.040.99; 37.100.01
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
This document has not been edited by the ISO Central Secretariat.
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
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 SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 22028-5:2025(en)
DRAFT
ISO/DIS 22028-5:2025(en)
International
Standard
ISO/DIS 22028-5
ISO/TC 42
Photography and graphic
Secretariat: ANSI
technology — Extended colour
Voting begins on:
encodings for digital image storage,
manipulation and interchange —
Voting terminates on:
Part 5:
High dynamic range and wide
colour gamut encoding for still
images (HDR/WCG)
Photographie et technologie graphique — Codages par couleurs
étendues pour stockage, manipulation et échange d'image
numérique —
Partie 5: Plage dynamique élevée et codage large de la gamme de
couleurs pour les images fixes (HDR/WCG)
ICS: 37.040.99; 37.100.01
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
This document has not been edited by the ISO Central Secretariat. BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 22028-5:2025(en)
ii
ISO/DIS 22028-5:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and acronyms . 1
4 Requirements . 4
4.1 General introduction .4
4.2 Colour image encoding .4
4.2.1 General .4
4.2.2 Colour primaries and white point .4
4.2.3 Baseline colour encoding .5
4.3 Transfer functions .6
4.3.1 General .6
4.3.2 Hybrid Log-Gamma (HLG) system .6
4.3.3 Perceptual quantizer (PQ) system .7
4.4 Reference viewing environment .7
4.5 Reference display .7
4.5.1 General .7
4.5.2 Default reference display colour primaries .8
4.5.3 Default nominal peak luminance .8
4.5.4 Default black point .8
4.5.5 Default HDR reference white luminance .8
4.6 Metadata .8
4.6.1 General .8
4.6.2 Coding-independent code points for video signal type identification: CICP
metadata .9
4.6.3 Viewing environment metadata .9
4.6.4 Colour volume metadata .9
4.6.5 HDR reference white luminance metadata .10
4.6.6 Scene-referred metadata .10
5 Colour mapping . 10
5.1 General .10
5.2 Colour conversions . .10
Annex A (normative) Extended HDR/WCG colour encoding .12
Annex B (informative) ITU-R transfer functions .13
Annex C (informative) HDR signalling . 14
Annex D (informative) Workflows for the different transfer functions .15
Annex E (informative) Image states and linear light colorimetric interpretations . 17
Annex F (informative) Display tone mapping . 19
Annex G (informative) Tone mapping to SDR display .20
Bibliography .25

iii
ISO/DIS 22028-5:2025(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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO 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).
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.
A list of all parts in the ISO 22028 series can be found on the ISO website.
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/DIS 22028-5:2025(en)
Introduction
This document has been developed to meet the industry need for a complete, fully documented, publicly
available specification of high dynamic range (HDR) and wide colour gamut (WCG) image encodings for
digital still images.
High dynamic range images, that have been produced to look correct on high dynamic range displays, can
provide a better user experience than standard dynamic range images. High dynamic range images allow
a greater range of shadow and highlight detail to be conveyed, with sufficient precision and acceptable
artefacts, including sufficient separation of diffuse white and specular highlights.
Wide colour gamut images, in addition, can represent a wider range of colours and allow for better colour
reproduction. These two features are commonly bundled together. In this document, for simplicity, we will
refer to both such features using the HDR/WCG acronym.
ITU-R has published requirements and guidelines for HDR/WCG television production and exchange, the
foundation of the blooming HDR/WCG video and movie ecosystems. There are now a growing number of
HDR/WCG displays (Smartphones, TVs, computer displays) that consumers use in their daily life, but a
limited amount of HDR/WCG still image content is available.
In parallel, digital cameras improve over time and capture more and more dynamic range. To overcome the
limitations of sensing technology, HDR images can be generated by fusing several images captured with
different exposures. But so far, the digital still imaging industry has not settled on a reference HDR/WCG
image encoding for consumers.
The purpose of this document is to provide requirements and guidelines for colour encoding of HDR/WCG
still images. The digital still imaging industry will benefit from these requirements and guidelines. They
will help establish a standard and open HDR/WCG ecosystem, to take better advantage of HDR cameras and
displays. These colour encoding requirements and guidelines can be leveraged in the specification of HDR/
WCG file formats.
The encoding and decoding methods specified in this document are from ITU-R BT.2100, to ensure full
compatibility with existing HDR/WCG devices and the associated video and movie ecosystems. Metadata
is specified in this document to support the communication of scene-referred and display-referred image
states in accordance with ISO 22028-1.
The outline of this document is as follows. The scope is defined in Clause 1, the normative references are
listed in Clause 2. Clause 3 lists the terms, definitions, and acronyms. Clause 4 covers the colour image
encoding requirements. Clause 5 covers colour conversion algorithms recommended to render HDR/WCG
images for displays with various characteristics and in various viewing environments.
Annex A (normative) specifies the extended HDR/WCG colour encoding.
Annex B (informative) lists a selection of highly relevant ITU-R Rec. BT.2100 tables.
Annex C (informative) lists relevant ISO/IEC 23000-22 tables, that are related to metadata recommended in
this document.
Annex D (informative) presents different HDR workflows.
Annex E (informative) provides information about ISO 22028-1 image states and the linear light
interpretations of HDR image signal values specified in ITU-R BT.2100.
Annex F (informative) presents tone mapping options.
Annex G (informative) describes a default HDR to SDR tone mapping algorithm.

v
DRAFT International Standard ISO/DIS 22028-5:2025(en)
Photography and graphic technology — Extended colour
encodings for digital image storage, manipulation and
interchange —
Part 5:
High dynamic range and wide colour gamut encoding for still
images (HDR/WCG)
1 Scope
This document defines a set of colour image encodings for use in storage, transmission, and display of high
dynamic range and wide colour gamut (HDR/WCG) digital still images. It defines the colour encodings, the
mandatory and optional metadata, and the reference viewing conditions for HDR/WCG images.
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 22028-1, Photography and graphic technology — Extended colour encodings for digital image storage,
manipulation and interchange — Part 1: Architecture and requirements
ISO/IEC 23091-2, Information technology — Coding-independent code points — Part 2: Video
ISO/IEC/TR 23091-4, Information technology — Coding-independent code points — Part 4: Usage of video
signal type code points
Recommendation ITU-R BT.2100: Image parameter values for high dynamic range television for use in
production and international programme exchange
SMPTE ST 2113, SMPTE Standard — Colorimetry of P3 Color Spaces
3 Terms, definitions and acronyms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological 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
coding-independent code points for video signal type identification
CICP
metadata that describes the colour image characteristics of the associated picture

ISO/DIS 22028-5:2025(en)
3.2
colour image encoding
digital encoding of the colour values for a digital image, including the specification of a colour space encoding,
together with any information necessary to properly interpret the colour values such as the image state, the
intended image viewing environment, and the reference medium
[SOURCE: ISO 22028-1:2016, 3.9, modified — Notes to entry were deleted.]
3.3
colour volume
space of all colours and intensities that a device or signal can reproduce or convey
[SOURCE: ISO/IEC TR 23091-4:2021, 3.6/ITU-T H.SUPPLEMENT 19]
3.4
content colour volume
CCV
metadata that describes the colour volume (colour primaries, white point, and luminance range)
characteristics of the associated picture
3.5
content light level
CLL
metadata that describes the light level characteristics (maximum and average) of the associated picture
3.6
display light
image values that result from applying the reference EOTF to the encoded image signal values
3.7
display viewing colorimetry
colorimetry appropriate for a targeted display with specified viewing conditions
Note 1 to entry: The display viewing colorimetry typically depends on the creative intent for the content.
3.8
display referred
image state associated with image data that represents the colour-space coordinates of the elements of an
image that has undergone colour-rendering appropriate for a specified display and viewing conditions
3.9
electrical-electrical transfer function
EETF
transfer function that adjusts the electronic signal, e.g. to tone map it to a lower display range
3.10
electro-optical transfer function
EOTF
transfer function which converts the non-linear signal into display light
3.11
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
higher than that of a standard dynamic range encoding, and a wider range of colours with more saturated
colours than standard colour gamut encodings
3.12
high dynamic range image
HDR image
image that contains wider variations in brightness, with a dynamic range significantly higher than that of a
standard dynamic range image
ISO/DIS 22028-5:2025(en)
3.13
HDR reference white
HDR signal level that would typically result from a 100 % Lambertian reflector placed at the centre of
interest within a scene under controlled lighting
Note 1 to entry: This is commonly referred to as diffuse white in the HDR content.
Note 2 to entry: The HDR reference white can be used as an anchor for HDR and SDR content compositing. The HDR
reference white is the HDR signal level typically reached by nominal peak SDR.
3.14
HDR reference white luminance
Luminance in cd/m resulting from the HDR reference white
Note 1 to entry: The HDR reference white results in a nominal luminance of 203 cd/m2 on the reference display
defined in 4.5.
3.15
highlights
image pixels with signal levels higher than the HDR reference white
3.16
image
data structure that contains pixels and image-related data
[SOURCE: ISO/IEC 12087-1:1995, 3.1.3]
3.17
mastering display
a display that is used or targeted for viewing while authoring the content
3.18
mastering display colour volume
MDCV
metadata that identifies the colour volume (the colour primaries, white point chromaticity, and luminance
range) of a mastering display
[SOURCE: SMPTE ST 2086]
3.19
nominal peak luminance
luminance resulting on a display from the specified encoding peak white signal level
Note 1 to entry: The peak white signal level is specified to be lower than the peak signal level for narrow range
encodings.
3.20
opto-electronic transfer function
OETF
transfer function that converts scene light into non-linear signal values
3.21
opto-optical transfer function
OOTF
transfer function that converts scene light to display light
3.22
scene light
image values that result from applying the inverse reference OETF to the encoded image signal values
3.23
transfer function
single variable, monotonic mathematical function applied individually to one or more colour channels

ISO/DIS 22028-5:2025(en)
3.24
wide colour gamut
WCG
gamut that has saturated colour primaries and includes a broad range of saturated colours
Note 1 to entry: It is wider than a standard colour gamut such as sRGB.
Note 2 to entry: WCG encodings provide a means to encode images with more saturated colours than standard colour
gamut encodings, to represent a wider range of colours and allow for better colour reproduction.
4 Requirements
4.1 General introduction
The colour image encodings specified in this document conform to the requirements defined in
ISO 22028-1:2016, Clause 5, and include a colour space representation, associated metadata, a reference
viewing environment, and a reference medium.
Colour image encoding and transfer functions are specified in 4.2 and 4.3 respectively. The reference viewing
environment and the reference display are defined in 4.4 and in 4.5 respectively. These subclauses provide
context for interpreting the intended colour appearance of the encoded image colorimetry. The associated
metadata are specified in 4.6. The most relevant ITU-R BT.2100 properties are referred to in Annex B of this
document.
4.2 Colour image encoding
4.2.1 General
Two sets of colour encodings are defined, baseline and extended. Images shall conform either to the baseline
colour encoding defined in 4.2.3, or to the extended colour encoding defined in Annex A. Image readers shall
support the baseline colour encoding, and may support the extended colour encoding.
The baseline colour encoding is recommended for cameras, TVs, and image readers on other consumer
devices. It is fully compatible with ITU-R BT.2100 and recommended for image exchanges with wider
viewing compatibility. The extended colour encoding is intended for applications where dedicated hardware
and/or software are used.
4.2.2 Colour primaries and white point
Images shall use the colour primaries and white point, as defined in Table 2, System colorimetry, of
ITU-R BT.2100-3.
Table 1 reproduces the chromaticity coordinates of the RGB primaries and white point of the colour encoding
space specified in ITU-R BT.2100.

ISO/DIS 22028-5:2025(en)
Table 1 — Chromaticity coordinates of the RGB primaries and white point of the colour encoding space
Values
Chromaticity coordinates
Parameter
(CIE, 1931)
Optical spectrum (informative)
x y
Red primary (R) monochromatic 630 nm 0,708 0,292
Primary
Green primary (G) monochromatic 532 nm 0,170 0,797
colours
Blue primary (B) monochromatic 467 nm 0,131 0,046
CIE standard illuminant D65 per ISO/
Reference White 0,312 7 0,329 0
CIE 11664-2
Colour matching functions CIE 1931
4.2.3 Baseline colour encoding
Images conforming to the baseline colour encoding shall comply with the specifications defined in Table 9 in
ITU-R BT.2100-3. Images shall use the non-constant luminance Y', C' , C' signal format defined in Table 6 in
B R
ITU-R BT.2100-3.
Table 2 partially reproduces the Table 9 of ITU-R BT.2100-3.
Table 2 — Baseline colour encoding specification
Parameter Value
Coded signal Y', C' , C'
B R
Coding format n = 10, 12 bits per component
Quantization of Y' Narrow range Full range
(resulting values that exceed the
n−8 n
video data range should be clipped
D = Round [(219 × E′ + 16) × 2 ] D = Round [(2 -1) × E′]
to the video data range)
Quantization of C' , C'
B R,
(resulting values that exceed the
n−8 n n-1
D = Round [(224 × E′ + 128) × 2 ] D = Round [(2 -1) × E′ + 2 ]
video data range should be clipped
to the video data range)
Quantization levels 10-bit coding 12-bit coding 10-bit coding 12-bit coding
Black
(Y' = 0) 64 256 0 0
DY'
Nominal Peak
(Y' = 1) 940 3 760 1 023 4 095
DY'
Achromatic
(C' = C' = 0) 512 2 048 512 2 048
B R
DC' , DC'
B R
Nominal Peak
(C' = C' = +0,5) 960 3 840 1 023 4 095
B R
DC' , DC'
B R
Nominal Peak
(C' = C' = -0,5) 64 256 1 1
B R
DC' , DC'
B R
4 through 16 through 0 through 0 through
Video data range
1 019 4 079 1 023 4 095
ISO/DIS 22028-5:2025(en)
Where:
Round( x ) Sign( x ) * Floor( | x | + 0,5 )
Floor( x ) the largest integer less than or equal to x
Sign( x )= 10; x>


00; x=


−<10; x

NOTE The narrow range representation is in widespread use in the video and broadcasting industries. The full
range representation is commonly used in the photographic industry.
4.3 Transfer functions
4.3.1 General
Two HDR/WCG colour encodings specified in ITU-R BT.2100 are widely adopted by video HDR/WCG
ecosystems: the hybrid log-gamma (HLG) encoding and perceptual quantization (PQ) encoding.
These encodings use the same colour primaries and white point but different transfer functions. Images
conforming to this document shall be encoded using an HLG transfer function (see 4.3.2), or a PQ transfer
function (see 4.3.3). Diagrams of the workflows using the different transfer functions are provided in
Annex D.
The HLG and PQ systems are designed to encode images for viewing on HDR/WCG displays: Scene light
captured by the camera may be adjusted to produce a desired image appearance when viewed on a display.
However, in some cases, imaging systems communicate estimated scene-referred colorimetry. This scene-
referred colorimetry should be indicated by using scene-referred metadata (Annex E provides details).
NOTE Scene-referred colorimetry images can be used in applications such as digital archiving, virtual scenes,
photorealistic compositing, some types of medical imaging, and machine vision.
4.3.2 Hybrid Log-Gamma (HLG) system
When scene light values are mapped into HLG signal values, this mapping shall be as specified by the HLG
Reference OETF defined in ITU-R BT.2100. When values are mapped in the inverse direction, this mapping
shall be according to the inverse of the HLG Reference OETF defined in ITU-R BT.2100.
When HLG signal values are mapped into display light values, this mapping shall be as specified by the HLG
Reference EOTF defined in ITU-R BT.2100.
When values are mapped in the inverse direction, this mapping shall be according to the inverse of the HLG
Reference EOTF defined in ITU-R BT.2100.
If the MDCV metadata is present, as defined in 4.6.4.2, its minimum and maximum luminance parameters
should be used for the derivation of the EOTF. When the MDCV metadata is not present, the minimum and
maximum luminance parameters of the reference display, as defined in 4.5, should be used for the derivation
of the EOTF.
ISO/DIS 22028-5:2025(en)
If the HLG signal values represent estimated scene colorimetry, this should be indicated using scene-referred
metadata. The inverse of the reference HLG opto-electronic transfer function (OETF) can be applied to the
encoded scene colorimetry to revert to linear light colorimetry (D.2, D.3, and Annex E provide details).
NOTE While the HLG encoding as defined in ITU-R BT.2100 is by default scene-referred, with a fixed OETF and
a variable OOTF/EOTF that adapts to different display dynamic ranges, in practice the OETF might be adjusted by
the content creator based on viewing the resulting image on a display. Alternatively, the OETF might be adjusted
by automatic image tuning algorithms in the camera image processing pipeline or in the post processing software.
Consequently, HLG images encoded as defined by ITU-R BT.2100 do not necessarily represent the colorimetry of the
actual scene.
4.3.3 Perceptual quantizer (PQ) system
When PQ signal values are mapped into display light values, this mapping shall be as specified by the
Reference PQ EOTF defined in ITU-R BT.2100. When values are mapped in the inverse direction, this
mapping shall be according to the inverse of the Reference PQ EOTF defined in ITU-R BT.2100.
When scene light values are mapped into PQ signal values, this mapping shall be as specified by the Reference
PQ OETF defined in ITU-R BT.2100. When values are mapped in the inverse direction, this mapping shall be
according to
...

International
Standard
First edition
Photography and graphic
2026-05
technology — Extended colour
encodings for digital image storage,
manipulation and interchange —
Part 5:
High dynamic range and wide
colour gamut encoding for still
images (HDR/WCG)
Photographie et technologie graphique — Codages par couleurs
étendues pour stockage, manipulation et échange d'image
numérique —
Partie 5: Plage dynamique élevée et codage large de la gamme de
couleurs pour les images fixes (HDR/WCG)
PROOF/ÉPREUVE
Reference number
© ISO 2026
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and acronyms . 1
4 Requirements . 4
4.1 Overview .4
4.2 Colour image encoding .4
4.2.1 General .4
4.2.2 Colour primaries and white point .4
4.2.3 Baseline colour encoding .5
4.3 Transfer functions .6
4.3.1 General .6
4.3.2 Hybrid Log-Gamma (HLG) system .6
4.3.3 Perceptual quantizer (PQ) system .7
4.4 Reference viewing environment .7
4.5 Reference display .7
4.5.1 General .7
4.5.2 Default reference display colour primaries .8
4.5.3 Default nominal peak luminance .8
4.5.4 Default black point .8
4.5.5 Default HDR reference white luminance .8
4.6 Metadata .8
4.6.1 General .8
4.6.2 Coding-independent code points for video signal type identification – CICP
metadata .9
4.6.3 Viewing environment metadata .9
4.6.4 Colour volume metadata .9
4.6.5 HDR reference white luminance metadata .10
4.6.6 Scene-referred metadata .10
5 Colour mapping . 10
5.1 General .10
5.2 Colour conversions . .10
Annex A (normative) Extended HDR/WCG colour encoding .12
Annex B (informative) ITU-R transfer functions .13
Annex C (informative) HDR signalling . 14
Annex D (informative) Workflows for the different transfer functions .15
Annex E (informative) Image states and linear light colorimetric interpretations . 17
Annex F (informative) Display tone mapping . 19
Annex G (informative) Tone mapping to SDR display .20
Bibliography .25
PROOF/ÉPREUVE
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 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. 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 const-
5te 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.
This first edition of ISO 22028-5 cancels and replaces the first edition (ISO/TS 22028-5:2023), which has
been technically revised.
A list of all parts in the ISO 22028 series can be found on the ISO website.
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.
PROOF/ÉPREUVE
iv
Introduction
This document has been developed to meet the industry need for a complete, fully documented, publicly
available specification of high dynamic range (HDR) and wide colour gamut (WCG) image encodings for
digital still images.
High dynamic range images, that have been produced to look correct on high dynamic range displays, can
provide a better user experience than standard dynamic range images. High dynamic range images allow
a greater range of shadow and highlight details to be conveyed, with sufficient precision and acceptable
artefacts, including sufficient separation of diffuse white and specular highlights.
Wide colour gamut images, in addition, can represent a wider range of colours and allow for better colour
reproduction. These two features are commonly bundled together. This document, for simplicity, refers to
both such features using the HDR/WCG acronym.
ITU-R has published requirements and guidelines for HDR/WCG television production and exchange, the
foundation of the blooming HDR/WCG video and movie ecosystems. There are now a growing number of
HDR/WCG displays (Smartphones, TVs, computer displays) that consumers use in their daily life, but a
limited amount of HDR/WCG still image content is available.
In parallel, digital cameras improve over time and capture more and more dynamic range. To overcome the
limitations of sensing technology, HDR images can be generated by fusing several images captured with
different exposures. But so far, the digital still imaging industry has not settled on a reference HDR/WCG
image encoding for consumers.
The purpose of this document is to provide requirements and guidelines for colour encoding of HDR/WCG
still images. The digital still imaging industry will benefit from these requirements and guidelines. They
will help establish a standard and open HDR/WCG ecosystem, to take better advantage of HDR cameras and
displays. These colour encoding requirements and guidelines can be leveraged in the specification of HDR/
WCG file formats.
The encoding and decoding methods specified in this document are from ITU-R BT.2100-3, to ensure full
compatibility with existing HDR/WCG devices and the associated video and movie ecosystems. Metadata
is specified in this document to support the communication of scene-referred and display-referred image
states in accordance with ISO 22028-1.
PROOF/ÉPREUVE
v
International Standard ISO 22028-5:2026(en)
Photography and graphic technology — Extended colour
encodings for digital image storage, manipulation and
interchange —
Part 5:
High dynamic range and wide colour gamut encoding for still
images (HDR/WCG)
1 Scope
This document defines a set of colour image encodings for use in storage, transmission, and display of high
dynamic range and wide colour gamut (HDR/WCG) digital still images. It defines the colour encodings, the
mandatory and optional metadata, and the reference viewing conditions for HDR/WCG images.
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 23091-2, Information technology — Coding-independent code points — Part 2: Video
ISO/IEC/TR 23091-4, Information technology — Coding-independent code points — Part 4: Usage of video
signal type code points
Recommendation ITU-R BT.2100-3:2025, Image parameter values for high dynamic range television for use in
production and international programme exchange
SMPTE ST 2113, SMPTE Standard — Colorimetry of P3 Color Spaces
3 Terms, definitions and acronyms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological 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
coding-independent code points for video signal type identification
CICP
metadata that describes the colour image characteristics of the associated picture
PROOF/ÉPREUVE
3.2
colour image encoding
digital encoding of the colour values for a digital image, including the specification of a colour space encoding,
together with any information necessary to properly interpret the colour values such as the image state, the
intended image viewing environment, and the reference medium
[SOURCE: ISO 22028-1:2016, 3.9, modified — Notes to entry were deleted.]
3.3
colour volume
space of all colours and intensities that a device or signal can reproduce or convey
[SOURCE: ISO/IEC TR 23091-4:2021, 3.6]
3.4
content colour volume
CCV
metadata that describes the colour volume (colour primaries, white point, and luminance range)
characteristics of the associated picture
3.5
content light level
CLL
metadata that describes the light level characteristics (maximum and average) of the associated picture
3.6
display light
image values that result from applying the reference EOTF to the encoded image signal values
3.7
display viewing colorimetry
colorimetry appropriate for a targeted display with specified viewing conditions
Note 1 to entry: The display viewing colorimetry typically depends on the creative intent for the content.
3.8
display referred
image state associated with image data that represents the colour-space coordinates of the elements of an
image that has undergone colour-rendering appropriate for a specified display and viewing conditions
3.9
electrical-electrical transfer function
EETF
transfer function that adjusts the electronic signal, e.g. to tone map it to a lower display range
3.10
electro-optical transfer function
EOTF
transfer function which converts the non-linear signal into display light (3.6)
3.11
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
higher than that of a standard dynamic range encoding, and a wider range of colours with more saturated
colours than standard colour gamut encodings
3.12
high dynamic range image
HDR image
image that contains wider variations in brightness, with a dynamic range significantly higher than that of a
standard dynamic range image
PROOF/ÉPREUVE
3.13
HDR reference white
HDR signal level that would typically result from a 100 % Lambertian reflector placed at the centre of
interest within a scene under controlled lighting
Note 1 to entry: This is commonly referred to as diffuse white in the HDR content.
Note 2 to entry: The HDR reference white can be used as an anchor for HDR and SDR content compositing. The HDR
reference white is the HDR signal level typically reached by nominal peak SDR.
3.14
HDR reference white luminance
luminance in cd/m resulting from the HDR reference white
Note 1 to entry: The HDR reference white results in a nominal luminance of 203 cd/m2 on the reference display
defined in 4.5.
3.15
highlights
image pixels with signal levels higher than the HDR reference white
3.16
image
data structure that contains pixels and image-related data
[SOURCE: ISO/IEC 12087-1:1995, 3.1.3]
3.17
mastering display
display that is used or targeted for viewing while authoring the content
3.18
mastering display colour volume
MDCV
metadata that identifies the colour volume (the colour primaries, white point chromaticity, and luminance
range) of a mastering display
[SOURCE: SMPTE ST 2086:2018]
3.19
nominal peak luminance
luminance resulting on a display from the specified encoding peak white signal level
Note 1 to entry: The peak white signal level is specified to be lower than the peak signal level for narrow range
encodings.
3.20
opto-electronic transfer function
OETF
transfer function that converts scene light into non-linear signal values
3.21
opto-optical transfer function
OOTF
transfer function that converts scene light to display light (3.6)
3.22
scene light
image values that result from applying the inverse reference OETF to the encoded image signal values
3.23
transfer function
single variable, monotonic mathematical function applied individually to one or more colour channels
PROOF/ÉPREUVE
3.24
wide colour gamut
WCG
gamut that has saturated colour primaries and includes a broad range of saturated colours
Note 1 to entry: It is wider than a standard colour gamut such as sRGB.
Note 2 to entry: WCG encodings provide a means to encode images with more saturated colours than standard colour
gamut encodings, to represent a wider range of colours and allow for better colour reproduction.
4 Requirements
4.1 Overview
The colour image encodings specified in this document conform to the requirements defined in
ISO 22028-1:2016, Clause 5, and include a colour space representation, associated metadata, a reference
viewing environment, and a reference medium.
Colour image encoding and transfer functions are specified in 4.2 and 4.3 respectively. The reference viewing
environment and the reference display are defined in 4.4 and in 4.5 respectively. These subclauses provide
context for interpreting the intended colour appearance of the encoded image colorimetry. The associated
metadata are specified in 4.6. The most relevant ITU-R BT.2100-3 properties are referred to in Annex B.
4.2 Colour image encoding
4.2.1 General
Two sets of colour encodings are defined, baseline and extended. Images shall conform either to the baseline
colour encoding defined in 4.2.3, or to the extended colour encoding defined in Annex A. Image readers shall
support the baseline colour encoding and may support the extended colour encoding.
The baseline colour encoding is recommended for cameras, TVs, and image readers on other consumer
devices. It is fully compatible with ITU-R BT.2100-3 and recommended for image exchanges with wider
viewing compatibility. The extended colour encoding is intended for applications where dedicated hardware
and/or software are used.
4.2.2 Colour primaries and white point
Images shall use the colour primaries and white point, as defined in Table 2, System colorimetry, of
ITU-R BT.2100-3.
Table 1 reproduces the chromaticity coordinates of the RGB primaries and white point of the colour encoding
space specified in ITU-R BT.2100-3.
PROOF/ÉPREUVE
Table 1 — Chromaticity coordinates of the RGB primaries and white point of the colour encoding
space
Values
Chromaticity coordinates
Parameter
(CIE, 1931)
Optical spectrum (informative)
x y
Red primary (R) monochromatic 630 nm 0,708 0,292
Primary
Green primary (G) monochromatic 532 nm 0,170 0,797
colours
Blue primary (B) monochromatic 467 nm 0,131 0,046
CIE standard illuminant D65 per ISO/
Reference White 0,312 7 0,329 0
CIE 11664-2
Colour matching functions CIE 1931
4.2.3 Baseline colour encoding
Images conforming to the baseline colour encoding shall comply with the specifications defined in
ITU-R BT.2100-3:2025, Table 9. Images shall use the non-constant luminance Y', C' , C' signal format defined
B R
in ITU-R BT.2100-3:2025, Table 6.
Table 2 partially reproduces the ITU-R BT.2100-3:2025, Table 9.
Table 2 — Baseline colour encoding specification
Parameter Value
Coded signal Y', C' , C'
B R
Coding format n = 10, 12 bits per component
Quantization of Y' Narrow range Full range
(resulting values that exceed the
n−8 n
video data range should be clipped
D = Round [(219 × E′ + 16) × 2 ] D = Round [(2 -1) × E′]
to the video data range)
Quantization of C' , C'
B R,
(resulting values that exceed the
n−8 n n-1
D = Round [(224 × E′ + 128) × 2 ] D = Round [(2 -1) × E′ + 2 ]
video data range should be clipped
to the video data range)
Quantization levels 10-bit coding 12-bit coding 10-bit coding 12-bit coding
Black
(Y' = 0) 64 256 0 0
DY'
Nominal peak
(Y' = 1) 940 3 760 1 023 4 095
DY'
Achromatic
(C' = C' = 0) 512 2 048 512 2 048
B R
DC' , DC'
B R
Nominal peak
(C' = C' = +0,5) 960 3 840 1 023 4 095
B R
DC' , DC'
B R
Nominal peak
(C' = C' = -0,5) 64 256 1 1
B R
DC' , DC'
B R
4 through 16 through 0 through 0 through
Video data range
1 019 4 079 1 023 4 095
PROOF/ÉPREUVE
where:
Round (x) = Sign(x) × Floor(|x| + 0,5)
Floor (x) is the largest integer less than or equal to x
Sign (x) =

10; x 


00; x 


10; x


NOTE The narrow range representation is in widespread use in the video and broadcasting industries. The full
range representation is commonly used in the photographic industry.
4.3 Transfer functions
4.3.1 General
Two HDR/WCG colour encodings specified in ITU-R BT.2100-3 are widely adopted by video HDR/WCG
ecosystems: the hybrid log-gamma (HLG) encoding and perceptual quantization (PQ) encoding.
These encodings use the same colour primaries and white point but different transfer functions. Images
conforming to this document shall be encoded using an HLG transfer function (see 4.3.2), or a PQ transfer
function (see 4.3.3). Diagrams of the workflows using the different transfer functions are provided in
Annex D.
The HLG and PQ systems are designed to encode images for viewing on HDR/WCG displays: Scene light
captured by the camera may be adjusted to produce a desired image appearance when viewed on a display.
However, in some cases, imaging systems communicate estimated scene-referred colorimetry. This scene-
referred colorimetry should be indicated by using scene-referred metadata (Annex E provides details).
NOTE Scene-referred colorimetry images can be used in applications such as digital archiving, virtual scenes,
photorealistic compositing, some types of medical imaging, and machine vision.
4.3.2 Hybrid Log-Gamma (HLG) system
When scene light values are mapped into HLG signal values, this mapping shall be as specified by the HLG
Reference OETF defined in ITU-R BT.2100-3. When values are mapped in the inverse direction, this mapping
shall be according to the inverse of the HLG Reference OETF defined in ITU-R BT.2100-3.
When HLG signal values are mapped into display light values, this mapping shall be as specified by the HLG
Reference EOTF defined in ITU-R BT.2100-3.
When values are mapped in the inverse direction, this mapping shall be according to the inverse of the HLG
Reference EOTF defined in ITU-R BT.2100-3.
If the MDCV metadata is present, as defined in 4.6.4.2, its minimum and maximum luminance parameters
should be used for the derivation of the EOTF. When the MDCV metadata is not present, the minimum and
maximum luminance parameters of the reference display, as defined in 4.5, should be used for the derivation
of the EOTF.
PROOF/ÉPREUVE
If the HLG signal values represent estimated scene colorimetry, this should be indicated using scene-referred
metadata. The inverse of the reference HLG opto-electronic transfer function (OETF) can be applied to the
encoded scene colorimetry to revert to linear light colorimetry (D.2, D.3, and Annex E provide details).
NOTE While the HLG encoding as defined in ITU-R BT.2100-3 is by default scene-referred, with a fixed OETF
and a variable OOTF/EOTF that adapts to different display dynamic ranges, in practice the OETF can be adjusted
by the content creator based on viewing the resulting image on a display. Alternatively, the OETF can be adjusted
by automatic image tuning algorithms in the camera image processing pipeline or in the post processing software.
Consequently, HLG images encoded as defined by ITU-R BT.2100-3 do not necessarily represent the colorimetry of the
actual scene.
4.3.3 Perceptual quantizer (PQ) system
When PQ signal values are mapped into display light values, this mapping shall be as specified by the
reference PQ EOTF defined in ITU-R BT.2100-3. When values are mapped in the inverse direction, this
mapping shall be according to the inverse of the reference PQ EOTF defined in ITU-R BT.2100-3.
When scene light values are mapped into PQ signal values, this mapping shall be as specified by the reference
PQ OETF defined in ITU-R BT.2100-3. When values are mapped in the inverse direction, this mapping shall
be according to the inverse of the reference PQ OETF defined in ITU-R BT.2100-3.
If the PQ signal values represent estimated scene colorimetry, this should be indicated by using scene-
referred metadata. When decoding the signal, the inverse of the reference PQ OETF can be applied to the
encoded scene colorimetry to revert to linear light colorimetry (D.4, D.5 and Annex E provide details).
NOTE The PQ encoding as defined in ITU-R BT.2100-3 is by default display-referred.
4.4 Reference viewing environment
Table 3 specifies parameters to establish a reference viewing environment in which images with
display viewing colorimetry and conforming to this document are intended to be viewed, as required in
ISO 22028-1:2016, 5.4.4.
Table 3 — Reference viewing environment specification
Parameter Value
Colour temperature
Neutral grey at CIE standard illuminant D65
of surround and periphery
Luminance of surround 5 cd/m
Luminance of periphery ≤5 cd/m
Spatial distribution No direct specular light sources shall be incident upon the eyes of
of ambient lighting the observer or the display.
NOTE 1 This reference viewing environment applies to display-viewing colorimetry, not to scene-referred
colorimetry.
NOTE 2 “surround” is the area surrounding a display that can affect the adaptation of the eye, typically the wall or
curtain behind the display; “periphery” is the remaining environment outside of the surround.
4.5 Reference display
4.5.1 General
Different high dynamic range and wide colour gamut displays can serve as reference media for HDR/
WCG images. While ITU-R BT.2100-3 defines minimal requirements for HDR reference displays,
ISO/IEC TR 23091-4 provides several HDR mastering display colour volume, i.e. MDCV, (see SMPTE ST 2086
and ISO/IEC 23000-22) descriptions for HDR reference displays, which represent displays widely used in
production and video content workflows. When such metadata is present, its information should be used
PROOF/ÉPREUVE
for the determination of the reference display’s parameters, such as its colour primaries, white point
chro
...

ISO/PRF 22028-5:2026(en)
ISO /TC 42
Secretariat: ANSI
Date: 2026-02-18xx
Photography and graphic technology — Extended colour encodings
for digital image storage, manipulation and interchange — —
Part 5:
High dynamic range and wide colour gamut encoding for still images
(HDR/WCG)
Photographie et technologie graphique — Codages par couleurs étendues pour stockage, manipulation et
échange d'image numérique —
Partie 5: Plage dynamique élevée et codage large de la gamme de couleurs pour les images fixes (HDR/WCG)
PROOF
ISO/PRF 22028-5:2026(en)
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
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO/PRF 22028-5:2026(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and acronyms . 1
4 Requirements . 4
4.1 Overview . 4
4.2 Colour image encoding . 4
4.3 Transfer functions . 6
4.4 Reference viewing environment . 7
4.5 Reference display . 8
4.6 Metadata . 8
5 Colour mapping . 10
5.1 General . 10
5.2 Colour conversions . 11
Annex A (normative) Extended HDR/WCG colour encoding . 12
Annex B (informative) ITU-R transfer functions . 13
Annex C (informative) HDR signalling . 14
Annex D (informative) Workflows for the different transfer functions . 15
Annex E (informative) Image states and linear light colorimetric interpretations . 18
Annex F (informative) Display tone mapping . 20
Annex G (informative) Tone mapping to SDR display . 21
Bibliography . 26

iii
ISO/PRF 22028-5:2026(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(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 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. 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 const-
5te 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.
This first edition of ISO 22028-5 cancels and replaces the first edition (ISO/TS 22028-5:2023), which has been
technically revised.
A list of all parts in the ISO 22028 series can be found on the ISO website.
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/PRF 22028-5:2026(en)
Introduction
This document has been developed to meet the industry need for a complete, fully documented, publicly
available specification of high dynamic range (HDR) and wide colour gamut (WCG) image encodings for digital
still images.
High dynamic range images, that have been produced to look correct on high dynamic range displays, can
provide a better user experience than standard dynamic range images. High dynamic range images allow a
greater range of shadow and highlight details to be conveyed, with sufficient precision and acceptable
artefacts, including sufficient separation of diffuse white and specular highlights.
Wide colour gamut images, in addition, can represent a wider range of colours and allow for better colour
reproduction. These two features are commonly bundled together. This document, for simplicity, refers to
both such features using the HDR/WCG acronym.
ITU-R has published requirements and guidelines for HDR/WCG television production and exchange, the
foundation of the blooming HDR/WCG video and movie ecosystems. There are now a growing number of
HDR/WCG displays (Smartphones, TVs, computer displays) that consumers use in their daily life, but a limited
amount of HDR/WCG still image content is available.
In parallel, digital cameras improve over time and capture more and more dynamic range. To overcome the
limitations of sensing technology, HDR images can be generated by fusing several images captured with
different exposures. But so far, the digital still imaging industry has not settled on a reference HDR/WCG image
encoding for consumers.
The purpose of this document is to provide requirements and guidelines for colour encoding of HDR/WCG still
images. The digital still imaging industry will benefit from these requirements and guidelines. They will help
establish a standard and open HDR/WCG ecosystem, to take better advantage of HDR cameras and displays.
These colour encoding requirements and guidelines can be leveraged in the specification of HDR/WCG file
formats.
The encoding and decoding methods specified in this document are from ITU-R BT.2100-3, to ensure full
compatibility with existing HDR/WCG devices and the associated video and movie ecosystems. Metadata is
specified in this document to support the communication of scene-referred and display-referred image states
in accordance with ISO 22028-1.
The outline of this document is as follows. The scope is defined in Clause 1, the normative references are listed
in Clause 2. Clause 3 lists the terms, definitions, and acronyms. Clause 4 covers the colour image encoding
requirements. Clause 5 covers colour conversion algorithms recommended to render HDR/WCG images for
displays with various characteristics and in various viewing environments.
Annex A (normative) specifies the extended HDR/WCG colour encoding.
Annex B (informative) lists a selection of highly relevant ITU-R Rec. BT.2100-3 tables.
Annex C (informative) lists relevant ISO/IEC 23000-22 tables, that are related to metadata recommended in
this document.
Annex D (informative) presents different HDR workflows.
Annex E (informative) provides information about ISO 22028-1 image states and the linear light
interpretations of HDR image signal values specified in ITU-R BT.2100-3.
Annex F (informative) presents tone mapping options.
v
ISO/PRF 22028-5:2026(en)
Annex G (informative) describes a default HDR to SDR tone mapping algorithm.
vi
ISO/PRF 22028-5:2026(en)
Photography and graphic technology — Extended colour encodings
for digital image storage, manipulation and interchange — —
Part 5:
High dynamic range and wide colour gamut encoding for still images
(HDR/WCG)
1 Scope
This document defines a set of colour image encodings for use in storage, transmission, and display of high
dynamic range and wide colour gamut (HDR/WCG) digital still images. It defines the colour encodings, the
mandatory and optional metadata, and the reference viewing conditions for HDR/WCG images.
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 23091--2, Information technology — Coding-independent code points — Part 2: Video
ISO/IEC/TR 23091--4, Information technology — Coding-independent code points — Part 4: Usage of video
signal type code points
Recommendation ITU-R BT.2100-3:2025, Image parameter values for high dynamic range television for use in
production and international programme exchange
SMPTE ST 2113, SMPTE Standard — Colorimetry of P3 Color Spaces
3 Terms, definitions and acronyms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological 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 3.1
coding-independent code points for video signal type identification
CICP
metadata that describes the colour image characteristics of the associated picture
3.2 3.2
colour image encoding
digital encoding of the colour values for a digital image, including the specification of a colour space encoding,
together with any information necessary to properly interpret the colour values such as the image state, the
intended image viewing environment, and the reference medium
[SOURCE: ISO 22028-1:2016, 3.9, modified — Notes to entry were deleted.]
ISO/PRF 22028-5:2026(en)
3.3 3.3
colour volume
space of all colours and intensities that a device or signal can reproduce or convey
[SOURCE: ISO/IEC TR 23091-4:2021, 3.6]
3.4 3.4
content colour volume
CCV
metadata that describes the colour volume (colour primaries, white point, and luminance range)
characteristics of the associated picture
3.5 3.5
content light level
CLL
metadata that describes the light level characteristics (maximum and average) of the associated picture
3.6 3.6
display light
image values that result from applying the reference EOTF to the encoded image signal values
3.7 3.7
display viewing colorimetry
colorimetry appropriate for a targeted display with specified viewing conditions
Note 1 to entry: The display viewing colorimetry typically depends on the creative intent for the content.
3.8 3.8
display referred
image state associated with image data that represents the colour-space coordinates of the elements of an
image that has undergone colour-rendering appropriate for a specified display and viewing conditions
3.9 3.9
electrical-electrical transfer function
EETF
transfer function that adjusts the electronic signal, e.g. to tone map it to a lower display range
3.10 3.10
electro-optical transfer function
EOTF
transfer function which converts the non-linear signal into display light (3.6(3.6))
3.11 3.11
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
higher than that of a standard dynamic range encoding, and a wider range of colours with more saturated
colours than standard colour gamut encodings
3.12 3.12
high dynamic range image
HDR image
image that contains wider variations in brightness, with a dynamic range significantly higher than that of a
standard dynamic range image
ISO/PRF 22028-5:2026(en)
3.13 3.13
HDR reference white
HDR signal level that would typically result from a 100 % Lambertian reflector placed at the centre of interest
within a scene under controlled lighting
Note 1 to entry: This is commonly referred to as diffuse white in the HDR content.
Note 2 to entry: The HDR reference white can be used as an anchor for HDR and SDR content compositing. The HDR
reference white is the HDR signal level typically reached by nominal peak SDR.
3.14 3.14
HDR reference white luminance
luminance in cd/m resulting from the HDR reference white
Note 1 to entry: The HDR reference white results in a nominal luminance of 203 cd/m2 on the reference display defined
in 4.54.5.
3.15 3.15
highlights
image pixels with signal levels higher than the HDR reference white
3.16 3.16
image
data structure that contains pixels and image-related data
[SOURCE: ISO/IEC 12087-1:1995, 3.1.3]
3.17 3.17
mastering display
a display that is used or targeted for viewing while authoring the content
3.18 3.18
mastering display colour volume
MDCV
metadata that identifies the colour volume (the colour primaries, white point chromaticity, and luminance
range) of a mastering display
[SOURCE: SMPTE ST 2086:2018]
3.19 3.19
nominal peak luminance
luminance resulting on a display from the specified encoding peak white signal level
Note 1 to entry: The peak white signal level is specified to be lower than the peak signal level for narrow range
encodings.
3.20 3.20
opto-electronic transfer function
OETF
transfer function that converts scene light into non-linear signal values
3.21 3.21
opto-optical transfer function
OOTF
transfer function that converts scene light to display light (3.6(3.6))
ISO/PRF 22028-5:2026(en)
3.22 3.22
scene light
image values that result from applying the inverse reference OETF to the encoded image signal values
3.23 3.23
transfer function
single variable, monotonic mathematical function applied individually to one or more colour channels
3.24 3.24
wide colour gamut
WCG
gamut that has saturated colour primaries and includes a broad range of saturated colours
Note 1 to entry: It is wider than a standard colour gamut such as sRGB.
Note 2 to entry: WCG encodings provide a means to encode images with more saturated colours than standard colour
gamut encodings, to represent a wider range of colours and allow for better colour reproduction.
4 Requirements
4.1 Overview
The colour image encodings specified in this document conform to the requirements defined in ISO 22028-
1:2016, Clause 5, and include a colour space representation, associated metadata, a reference viewing
environment, and a reference medium.
Colour image encoding and transfer functions are specified in 4.24.2 and 4.34.3 respectively. The reference
viewing environment and the reference display are defined in 4.44.4 and in 4.54.5 respectively. These
subclauses provide context for interpreting the intended colour appearance of the encoded image colorimetry.
The associated metadata are specified in 4.64.6. The most relevant ITU-R BT.2100-3 properties are referred
to in Annex BAnnex B.
4.2 Colour image encoding
4.2.1 General
Two sets of colour encodings are defined, baseline and extended. Images shall conform either to the baseline
colour encoding defined in 4.2.34.2.3,, or to the extended colour encoding defined in Annex AAnnex A. Image
readers shall support the baseline colour encoding and may support the extended colour encoding.
The baseline colour encoding is recommended for cameras, TVs, and image readers on other consumer
devices. It is fully compatible with ITU-R BT.2100-3 and recommended for image exchanges with wider
viewing compatibility. The extended colour encoding is intended for applications where dedicated hardware
and/or software are used.
4.2.2 Colour primaries and white point
Images shall use the colour primaries and white point, as defined in Table 2Table 2,, System colorimetry, of
ITU--R BT.2100-3.
Table 1Table 1 reproduces the chromaticity coordinates of the RGB primaries and white point of the colour
encoding space specified in ITU-R BT.2100-3.
ISO/PRF 22028-5:2026(en)
Table 1 — Chromaticity coordinates of the RGB primaries and white point of the colour encoding
space
Values
Chromaticity coordinates
Parameter
(CIE, 1931)
Optical spectrum (informative)
x y
Red primary (R) monochromatic 630 nm 0,708 0,292
Primary
Green primary (G) monochromatic 532 nm 0,170 0,797
colours
Blue primary (B) monochromatic 467 nm 0,131 0,046
CIE standard illuminant D65 per
Reference White 0,312 7 0,329 0
ISO/CIE 11664-2
Colour matching functions CIE 1931
4.2.3 Baseline colour encoding
Images conforming to the baseline colour encoding shall comply with the specifications defined in Table 9 in
ITU-R BT.2100-3.:2025, Table 9. Images shall use the non-constant luminance Y', C' , C' signal format defined
B R
in Table 6 in ITU-R BT.2100-3:2025, Table 6.
Table 2Table 2 partially reproduces the Table 9 of ITU-R BT.2100-3:2025, Table 9.
Table 2 — Baseline colour encoding specification
Parameter Value
Coded signal Y', C'B, C'R
Coding format n = 10, 12 bits per component
Quantization of Y' Narrow range Full range
(resulting values that exceed the
n−8 n
video data range should be
D = Round [(219 × E′ + 16) × 2 ] D = Round [(2 -1) × E′]
clipped to the video data range)
Quantization of C' , C'
B R,
(resulting values that exceed the
n−8 n n-1
D = Round [(224 × E′ + 128) × 2 ] D = Round [(2 -1) × E′ + 2 ]
video data range should be
clipped to the video data range)
Quantization levels 10-bit coding 12-bit coding 10-bit coding 12-bit coding
Black
(Y' = 0) 64 256 0 0
DY'
Nominal peak
(Y' = 1) 940 3 760 1 023 4 095
DY'
Achromatic
(C'B = C'R = 0) 512 2 048 512 2 048
DC'B, DC'R
Nominal peak
960 3 840 1 023 4 095
(C'B = C'R = +0,5)
ISO/PRF 22028-5:2026(en)
Parameter Value
DC'B, DC'R
Nominal peak
(C'B = C'R = -0,5) 64 256 1 1
DC'B, DC'R
4 through 16 through 0 through 0 through
Video data range
1 019 4 079 1 023 4 095
where:
Round( (x Sign( x ) *) × Floor( | (|x | + 0,5 )
)) =
Floor( (x ) is the largest integer less than or equal to x
1 ; 𝑥𝑥 > 0
Sign( (x )=) =
{ 0 ; 𝑥𝑥 = 0
−1 ; 𝑥𝑥 < 0
NOTE The narrow range representation is in widespread use in the video and broadcasting industries. The full range
representation is commonly used in the photographic industry.
4.3 Transfer functions
4.3.1 General
Two HDR/WCG colour encodings specified in ITU-R BT.2100-3 are widely adopted by video HDR/WCG
ecosystems: the hybrid log-gamma (HLG) encoding and perceptual quantization (PQ) encoding.
These encodings use the same colour primaries and white point but different transfer functions. Images
conforming to this document shall be encoded using an HLG transfer function (see 4.3.24.3.2),), or a PQ
transfer function (see 4.3.34.3.3).). Diagrams of the workflows using the different transfer functions are
provided in Annex DAnnex D.
The HLG and PQ systems are designed to encode images for viewing on HDR/WCG displays: Scene light
captured by the camera may be adjusted to produce a desired image appearance when viewed on a display.
However, in some cases, imaging systems communicate estimated scene-referred colorimetry. This scene-
referred colorimetry should be indicated by using scene-referred metadata (Annex E(Annex E provides
details).
NOTE Scene-referred colorimetry images can be used in applications such as digital archiving, virtual scenes,
photorealistic compositing, some types of medical imaging, and machine vision.
4.3.2 Hybrid Log-Gamma (HLG) system
When scene light values are mapped into HLG signal values, this mapping shall be as specified by the HLG
Reference OETF defined in ITU-R BT.2100-3. When values are mapped in the inverse direction, this mapping
shall be according to the inverse of the HLG Reference OETF defined in ITU-R BT.2100-3.
When HLG signal values are mapped into display light values, this mapping shall be as specified by the HLG
Reference EOTF defined in ITU-R BT.2100-3.
When values are mapped in the inverse direction, this mapping shall be according to the inverse of the HLG
Reference EOTF defined in ITU-R BT.2100-3.
ISO/PRF 22028-5:2026(en)
If the MDCV metadata is present, as defined in 4.6.4.24.6.4.2,, its minimum and maximum luminance
parameters should be used for the derivation of the EOTF. When the MDCV metadata is not present, the
minimum and maximum luminance parameters of the reference display, as defined in 4.54.5,, should be used
for the derivation of the EOTF.
If the HLG signal values represent estimated scene colorimetry, this should be indicated using scene-referred
metadata. The inverse of the reference HLG opto-electronic transfer function (OETF) can be applied to the
encoded scene colorimetry to revert to linear light colorimetry (D.2, D.3(D.2, D.3,, and Annex EAnnex E
provide details).
NOTE While the HLG encoding as defined in ITU-R BT.2100-3 is by default scene-referred, with a fixed OETF and a
variable OOTF/EOTF that adapts to different display dynamic ranges, in practice the OETF mightcan be adjusted by the
content creator based on viewing the resulting image on a display. Alternatively, the OETF mightcan be adjusted by
automatic image tuning algorithms in the camera image processing pipeline or in the post processing software.
Consequently, HLG images encoded as defined by ITU-R BT.2100-3 do not necessarily represent the colorimetry of the
actual scene.
4.3.3 Perceptual quantizer (PQ) system
When PQ signal values are mapped into display light values, this mapping shall be as specified by the reference
PQ EOTF defined in ITU-R BT.2100-3. When values are mapped in the inverse direction, this mapping shall be
according to the inverse of the reference PQ EOTF defined in ITU-R BT.2100-3.
When scene light values are mapped into PQ signal values, this mapping shall be as specified by the reference
PQ OETF defined in ITU-R BT.2100-3. When values are mapped in the inverse direction, this mapping shall be
according to the inverse of the reference PQ OETF defined in ITU-R BT.2100-3.
If the PQ signal values represent estimated scene colorimetry, this should be indicated by using scene-referred
metadata. When decoding the signal, the inverse of the reference PQ OETF can be applied to the encoded scene
colorimetry to revert to linear light colorimetry (D.4(D.4, Annex D.5, D.5 and Annex EAnnex E provide details).
NOTE The PQ encoding as defined in ITU-R BT.2100-3 is by default display-referred.
4.4 Reference viewing environment
Table 3Table 3 specifies parameters to establish a reference viewing environment in which images with
display viewing colorimetry and conforming to this document are intended to be viewed, as required in
ISO 22028-1:2016, 5.4.4.
Table 3 — Reference viewing environment specification
Parameter Value
Colour temperature
Neutral grey at CIE standard illuminant D65
of surround and periphery
Luminance of surround 5 cd/m
Luminance of periphery ≤5 cd/m
Spatial distribution No direct specular light sources shall be incident upon the eyes of
of ambient lighting the observer or the display.
NOTE 1 This reference viewing environment applies to display-viewing colorimetry, not to scene-referred
colorimetry.
NOTE 2 “surround” is the area surrounding a display that can affect the adaptation of the eye, typically the wall or
curtain behind the display; “periphery” is the remaining environment outside of the surround.
ISO/PRF 22028-5:2026(en)
4.5 Reference display
4.5.1 General
Different high dynamic range and wide colour gamut displays can serve as reference media for HDR/WCG
images. While ITU-R BT.2100-3 defines minimal requirements for HDR reference displays,
ISO/IEC TR 23091-4 provides several HDR mastering display colour volume, i.e. MDCV, (see SMPTE ST 2086
and ISO/IEC 23000-22) descriptions for HDR reference displays, which represent displays widely used in
production and video content workflows. When such metadata is present, its information should be used for
the determination of the reference display’s parameters, such as its colour primaries, white point
chromaticity, and luminance range (maximum and minimum).
In the following clausessubclauses, a default reference display is specified. It provides a default context for
interpreting the intended colour appearance of the encoded image colorimetry. 4.5.24.5.2 defines the default
reference display colour volume, 4.5.44.5.4 the default nominal peak luminance, and 4.5.54.5.5 the default
black point. Then, 4.5.54.5.5 defines the default HDR reference white luminance.
NOTE This default reference display does not necessarily apply to scene-referred images.
4.5.2 Default reference display colour primaries
The default display colour primaries shall be the P3-D65 colour primaries in accordance with SMPTE ST 2113.
If a different display is used as a mastering display, the colour primaries of that display should be indicated
using metadata, as defined in 4.6.4.24.6.4.2.
4.5.3 Default nominal peak luminance
The nominal peak luminance of the default reference display shall be 1 000 cd/m .
If a different display is used as a mastering display, the nominal peak luminance of that display should be
indicated using metadata, as defined in 4.6.4.24.6.4.2
4.5.4 Default black point
The minimum luminance of the default reference display shall be 0,000 5 cd/m .
If a different display is used as a mastering display, the minimum luminance of that display should be indicated
using metadata, as defined in 4.6.4.24.6.4.2
4.5.5 Default HDR reference white luminance
The default HDR reference white luminance shall be 203 cd/m .
NOTE This default HDR reference white luminance value is defined in ITU-R BT.2408-5 as the HDR reference white.
If the HDR reference white luminance for specific content has a different value, the HDR reference white
luminance for that content should be indicated using metadata, as defined in 4.6.54.6.5.
4.6 Metadata
4.6.1 General
This sub clausesubclause covers mandatory and optiona
...