• Weight
• Color
• Roughness
• IOR
• Roughness Anisotropy
• Anisotropy Tangent

Weight

The Specular Weight modulates the brightness of the specular Fresnel reflection (i.e. highlight) from the base dielectric.

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Color

A color tint applied to the specular highlight. For metals, this is a realistic effect where near the grazing edge the metal has a different color tint to the metal viewed straight on. For non-metals, this is not physically realistic (as non-metallic, dielectric surfaces do not have a colored specular highlight) but it can be useful artistically in some cases.

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Roughness

Controls the glossiness of the specular reflections. The roughness value controls the roughness of the "microsurface" which reflects the incoming light. This microsurface detail has the most noticeable effect on specular reflections. As in the diagram below, incoming rays tend to diverge more when reflected from rougher surfaces, thus the reflected light appears more blurry with smeared highlights.

_{In the limit of zero roughness a perfectly sharp mirror reflection occurs, while roughness 1 will create reflections that are close to a diffuse reflection.}

The brightness of the specular highlight is automatically linked to its size due to the energy-conserving nature of OpenPBR Surface. In the example below (with a map connected to the Specular Roughness to get variation in the specular highlight), all of the materials are reflecting the same amount of light. The rougher surface is spreading it out in multiple directions, while the smoother surface is reflecting a more concentrated amount of light.

_{'Microsurface' detail Varying the Specular Roughness of a metal).}

To get variation in the highlights of the surface, a map should be connected to the Specular Roughness. This will influence not only the brightness of the highlight but also its size and the sharpness of the environmental reflection.

_{Fingerprint texture -> Specular Roughness}

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IOR

The Specular IOR defines the index of refraction (IOR) of the base dielectric. Higher IORs produce a stronger specular reflection.

Note that the IOR value does not apply to metals (i.e. when Base Metalness is 1), whose reflectivity is controlled entirely by Base Color and Specular Color.

As well as the reflection strength, the Specular IOR determines the refraction into the interior of the base dielectric, affecting the look of non-metallic surfaces.

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Roughness Anisotropy

Roughness anisotropy refers to a directional bias in the surface roughness, which causes materials to appear rougher or glossier in certain directions. The default value for Anisotropy is 0 (or "isotropic") which means there is no directional bias. As you move the control towards 1.0, the surface is made more anisotropic in the U axis (so highlights are stretched along U, aligned with the local tangent defined by the Anisotropy Tangent).

Anisotropy is suitable for materials that have a clear brush direction such as brushed metal which has tiny grooves which form a 'stretched' anisotropic reflection. For example, the displaced ridges below shows how anisotropic surface geometry leads to a stretched highlight.

_{Many small ridges form together to create an effect which is the anisotropic highlight}

More information about Specular Anisotropy can be found here.

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Anisotropy Tangent

The tangent used to define the direction of the corresponding specular lobe when using Anisotropy.

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