National foreword

This British Standard is the UK implementation of ISO 21496‑1:2025.

The UK participation in its preparation was entrusted to Technical Committee CPW/42, Photography.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2025.

Foreword

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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.

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.

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

3 Terms, definitions, and acronyms

4 Gain map requirements

4.1 General

4.2 Gain map dimensions

4.3 Gain map colour components

4.4 Gain map quantization

4.5 Orientation

5 Metadata

5.1 General

5.2 Gain map metadata

5.3 Colorimetry metadata

6 Gain map application

6.1 General

6.2 Processing the gain map

6.3 Applying the gain map

Bibliography

BS ISO 21496-1:2025

Digital photography. Gain map metadata for image conversion - Dynamic range conversion

Current

Published:

31 Jul 2025