MAM2019: Eurographics Workshop on Material Appearance Modeling

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https://diglib.eg.org/handle/10.2312/2632807

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Browsing MAM2019: Eurographics Workshop on Material Appearance Modeling by Subject "Reflectance modeling"

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    Fresnel Equations Considered Harmful
    (The Eurographics Association, 2019) Hoffman, Naty; Klein, Reinhard and Rushmeier, Holly
    Microfacet shading models in film and game production have long used a simple approximation to the Fresnel equations, published by Schlick in 1994. Recently a growing number of film studios have transitioned to using the full Fresnel reflectance equations in lieu of Schlick's approximation. This transition has been facilitated by Gulbrandsen's 2014 parameterization which uses reflectance and edge tint instead of eta and kappa. Our recent investigations have found some unexpected drawbacks to this approach. In this presentation, we will show that in the context of RGB rendering (still by far the most common modality in film production), the Fresnel equations are actually less physically principled than Schlick's approximation. In addition, they are less robust in practice and less amenable to authoring. Most surprisingly, as commonly used the Fresnel equations result in less accurate matches to measured materials, compared to Schlick's approximation. The presentation primarily discusses metal reflectance, since our investigations so far have focused on metals.
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    Rendering Transparent Materials with a Complex Refractive Index: Semi-conductor and Conductor Thin Layers
    (The Eurographics Association, 2019) Gerardin, Morgane; Holzschuch, Nicolas; Martinetto, Pauline; Klein, Reinhard and Rushmeier, Holly
    During physical simulation of light transport, we separate materials between conductors and dielectrics. The former have a complex refractive index and are treated as opaque, the latter a real one and are treated as transparent. However, thin layers with a complex refractive index can become transparent if their thickness is small compared to the extinction coeffcient. This happens with thin metallic layers, but also with many pigments that are semiconductors: their extinction coeffcient (the imaginary part of their refractive index) is close to zero for part of the visible spectrum. Spectral effects inside these thin layers (attenuation and interference) result in dramatic color changes.