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KHR_materials_emissive_strength

Contributors

Copyright (C) 2021-2022 The Khronos Group Inc. All Rights Reserved. glTF is a trademark of The Khronos Group Inc. See Appendix for full Khronos Copyright Statement.

Status

Complete, Ratified by the Khronos Group

Dependencies

Written against the glTF 2.0 spec.

Exclusions

  • This extension must not be used on a material that also uses KHR_materials_unlit.

Overview

The core glTF 2.0 material model includes an emissiveFactor and an emissiveTexture to control the color and intensity of the light being emitted by the material, clamped to the range [0.0, 1.0]. However, in PBR environments with high-dynamic range reflections and lighting, stronger emission effects may be desirable.

In this extension, a new emissiveStrength scalar factor is supplied, that governs the upper limit of emissive strength per material.

Implementation Note: This strength can be colored and tempered using the core material's emissiveFactor and emissiveTexture controls, permitting the strength to vary across the surface of the material. Supplying values above 1.0 for emissiveStrength can have an influence on reflections, tonemapping, blooming, and more.

Physical Units

This extension supplies a unitless multiplier to the glTF 2.0 specification's emissive factor and texture. Including this multiplier does not alter the physical units defined in glTF 2.0's additional textures section, under the emissive texture.

Extending Materials

This section is non-normative.

Any material with an emissiveFactor (and optionally an emissiveTexture) can have its strength modulated or amplified by the inclusion of this extension. For example:

{
    "materials": [
        {
            "emissiveFactor": [
                1.0,
                1.0,
                1.0
            ],
            "emissiveTexture": {
                "index": 3
            },
            "extensions": {
                "KHR_materials_emissive_strength": {
                    "emissiveStrength": 5.0
                }
            }
        }
    ]
}

In the above example, the emissiveFactor has been set to its maximum value, to enable the emissiveTexture. The emissiveStrength has been set to 5.0, making the texture five times brighter than it otherwise would have been.

Parameters

The following parameters are contributed by the KHR_materials_emissive_strength extension:

Name Type Description Required
emissiveStrength number The strength adjustment to be multiplied with the material's emissive value. No, default: 1.0

Implementation Notes

This section is non-normative.

A typical (pseudocode) implementation might look like the following:

color += emissiveFactor.rgb * sRGB_to_Linear(emissiveTexture.rgb) * emissiveStrength;

Schema

Appendix: Full Khronos Copyright Statement

Copyright 2021-2022 The Khronos Group Inc.

This specification is protected by copyright laws and contains material proprietary to Khronos. Except as described by these terms, it or any components may not be reproduced, republished, distributed, transmitted, displayed, broadcast, or otherwise exploited in any manner without the express prior written permission of Khronos.

This specification has been created under the Khronos Intellectual Property Rights Policy, which is Attachment A of the Khronos Group Membership Agreement available at https://www.khronos.org/files/member_agreement.pdf. Khronos grants a conditional copyright license to use and reproduce the unmodified specification for any purpose, without fee or royalty, EXCEPT no licenses to any patent, trademark or other intellectual property rights are granted under these terms. Parties desiring to implement the specification and make use of Khronos trademarks in relation to that implementation, and receive reciprocal patent license protection under the Khronos IP Policy must become Adopters under the process defined by Khronos for this specification; see https://www.khronos.org/conformance/adopters/file-format-adopter-program.

Some parts of this Specification are purely informative and do not define requirements necessary for compliance and so are outside the Scope of this Specification. These parts of the Specification are marked as being non-normative, or identified as Implementation Notes.

Where this Specification includes normative references to external documents, only the specifically identified sections and functionality of those external documents are in Scope. Requirements defined by external documents not created by Khronos may contain contributions from non-members of Khronos not covered by the Khronos Intellectual Property Rights Policy.

Khronos makes no, and expressly disclaims any, representations or warranties, express or implied, regarding this specification, including, without limitation: merchantability, fitness for a particular purpose, non-infringement of any intellectual property, correctness, accuracy, completeness, timeliness, and reliability. Under no circumstances will Khronos, or any of its Promoters, Contributors or Members, or their respective partners, officers, directors, employees, agents or representatives be liable for any damages, whether direct, indirect, special or consequential damages for lost revenues, lost profits, or otherwise, arising from or in connection with these materials.

Khronos® and Vulkan® are registered trademarks, and ANARI™, WebGL™, glTF™, NNEF™, OpenVX™, SPIR™, SPIR‑V™, SYCL™, OpenVG™ and 3D Commerce™ are trademarks of The Khronos Group Inc. OpenXR™ is a trademark owned by The Khronos Group Inc. and is registered as a trademark in China, the European Union, Japan and the United Kingdom. OpenCL™ is a trademark of Apple Inc. and OpenGL® is a registered trademark and the OpenGL ES™ and OpenGL SC™ logos are trademarks of Hewlett Packard Enterprise used under license by Khronos. ASTC is a trademark of ARM Holdings PLC. All other product names, trademarks, and/or company names are used solely for identification and belong to their respective owners.