Gain Map
Images optimized for High Dynamic Range (HDR) displays have brighter highlights and more detailed shadows, resulting in an increased sense of realism and a greater impact. However, a major issue with the HDR content is the inconsistent appearance across different devices. There are several reasons, including varying capabilities of HDR displays and the different tone mapping methods implemented across software and platforms. Consequently, HDR content authors can neither control nor predict how their images will appear in other applications.
Gain Map provides a solution for a consistent and adaptive display of HDR images. Conceptually, this method combines both SDR and HDR renditions within a single image and interpolates between the two dynamically at display time. A Gain Map represents the quotient between the two renditions. The image file stores a Base rendition (SDR or HDR), the Gain Map, and some associated metadata. At display time, the Base image is combined with the scaled version of the Gain map, where the scale factor depends on the image metadata and the HDR capacity of the display. Gain Maps can be downsampled and compressed to save space.
An effort to standardize Gain Maps via ISO 21496-1 is currently under development.
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The Gain Map method has several advantages:
- It adapts dynamically to the current display and viewing conditions.
- It provides creative control to the image author instead of leaving the tone mapping to platform-specific behavior.
- It supports spatially-varying adjustments (local adaptation).
- It provides backward compatibility with the existing software.
- Its runtime display logic is simple and GPU-friendly.
Gain Map Specification Patent License
Adobe is the publisher of the Gain Map Specification describing a Gain Map-based approach for the storage, display, and tone mapping of High Dynamic Range images. Adobe provides the Gain Map Specification to the public to encourage the implementation of this file format in a compliant manner. This License is a patent license granted by Adobe to individuals and organizations that desire to develop, market, and/or distribute hardware and software that reads and/or writes image files compliant with the Gain Map Specification.
Grant of Rights
Subject to all the terms below and solely to permit the reading and writing of image files that comply with the Gain Map Specification, Adobe hereby grants, to all individuals and organizations who use the Gain Map Specification, a worldwide, royalty-free, nontransferable, nonexclusive right under all Essential Claims to make, have made, use, sell, offer to sell, import, and distribute only Compliant Implementations (and no other portion or function of any product or service).
“Compliant Implementation” means only any portion of any software or hardware product that reads or writes computer files compliant with the Gain Map Specification, solely for the implementation of, and solely to the extent any such product implements, the Gain Map Specification, excluding all Non-Gain Map Spec Functions performed by such portion or product.
“Non-Gain Map Spec Functions” means any function of any product that is not the implementation of any mandatory or optional feature of the Gain Map Specification. “Gain Map Specification” means any version of the Adobe Gain Map Specification made publicly available by Adobe (for example, version 1.0, dated February 2023).
“Essential Claim” means a claim of a patent, whenever and wherever issued, that Adobe has the right to license, without payment of royalty or other fees to any individual or organization, that is unavoidably infringed by implementation of the Gain Map Specification. A claim is unavoidably infringed by the Gain Map Specification only when it is not possible to avoid infringing that claim when conforming with such specification because there is no technically possible non-infringing alternative for achieving such conformity. “
Essential Claim” does not include any claim that is infringed by implementation of (a) enabling technology that may be necessary to make or use any product or portion thereof that complies with the Gain Map Specification but is not itself expressly set forth in the Gain Map Specification (for example, compiler technology and basic operating system technology), (b) technology not developed by Adobe and merely incorporated by reference in the Gain Map Specification, or (c) the implementation of or compliance with file formats other than that specified in the Gain Map Specification
Revocation
Adobe may revoke the rights granted under this License to any individual or organizational licensee in the event that such licensee or any of its affiliates brings any patent claim against Adobe, its affiliates, or any products or services of any of them, related to the reading or writing of files that comply with the Gain Map Specification or any other Compliant Implementation.
Any Compliant Implementation distributed under this License must include the following notice displayed in a prominent manner within its source code and documentation: "This product includes Gain Map technology under license by Adobe.”
No Warranty
The rights granted in this License are provided on an as-is basis without warranty of any kind, including without limitation any warranty of title or noninfringement. Nothing in this License shall be construed as (a) requiring the maintenance of any patent, (b) a warranty or representation as to the validity or scope of any patent, (c) a warranty or representation that the Gain Map Specification, or any product or service, will be free from infringement of any patent, (d) an agreement to bring or prosecute actions against any infringers of any patent, (e) conferring any right or license under any patent claim other than Essential Claims, or (f) authorizing any activity other than that expressly set forth in the Grant of Right.
Reservation of Rights
All rights not expressly granted herein by Adobe or any Adobe affiliate are reserved to them. By conducting any activity authorized by the Grant of Rights, the licensee acknowledges that, other than the rights expressly granted therein, no rights of any kind in, under, or related to, any patent held or controlled by Adobe or any Adobe affiliate, are granted by this License, and no activity of any kind is authorized under or with respect to any such patent, other than the activities expressly authorized under the Grant of Rights, solely to the extent set forth therein.