MAM2019: Eurographics Workshop on Material Appearance Modeling

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

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    Comparative Study of Layered Material Models
    (The Eurographics Association, 2019) Bati, Mégane; Pacanowski, Romain; Barla, Pascal; Klein, Reinhard and Rushmeier, Holly
    The accurate reproduction of layered materials is an important part of physically-based rendering applications. Since no exact analytical model exists for any configuration of layer stacks, available models make approximations. In this paper, we propose to evaluate them with a numerical approach: we simulate BRDFs and BTDFs for layered materials in order to compare existing models against a common reference. We show that: (1) no single model always outperforms the others and (2) significant differences remain between simulated and modeled materials. We analyse the reasons for these discrepancies and introduce immediate corrections.
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    What is the Reddening Effect and does it really exist?
    (The Eurographics Association, 2019) Clausen, Olaf; Marroquim, Ricardo; Fuhrmann, Arnulph; Weigand, Holger; Klein, Reinhard and Rushmeier, Holly
    The simulation of light-matter interaction is a major challenge in computer graphics. Particularly challenging is the modelling of light-matter interaction of rough surfaces, which contain several different scales of roughness where many different scattering phenomena take place. There are still appearance critical phenomena that are weakly approximated or even not included at all by current BRDF models. One of these phenomena is the reddening effect, which describes a tilting of the reflectance spectra towards long wavelengths especially in the specular reflection. The observation that the reddening effect takes place on rough surfaces is new and the characteristics and source of the reddening effect have not been thoroughly researched and explained. Furthermore, it was not even clear whether the reddening really exists or the observed effect resulted from measurement errors. In this work we give a short introduction to the reddening effect and show that it is indeed a property of the material reflectance function, and does not originate from measurement errors or optical aberrations.
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    MAM 2019: Frontmatter
    (Eurographics Association, 2019) Klein, Reinhard; Rushmeier, Holly; Klein, Reinhard and Rushmeier, Holly
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    On Visual Attractiveness of Anisotropic Effect Coatings
    (The Eurographics Association, 2019) Filip, Jiří; Kolafová, Martina; Klein, Reinhard and Rushmeier, Holly
    With the global trend in customer preference towards achromatic car colors, color designers in coating industry strive to create novel design-critical appearances based on novel effect pigments. At microscopic scale, the pigment particles allow to create specific optical effects like sparkle under directed lighting along with a specific texture in diffuse lighting, while at a macroscopic scale they create the appearance of angle-dependent color and a strong luminance contrast. Although individual particles in effect coatings exhibit anisotropic behavior, the majority of effect coatings exhibit isotropic appearance at a macroscopic scale due to a random orientation of the particles which can be explained with the manufacturing process of the coating. This paper demonstrates an visual appearances achievable by using anisotropic effect coatings based on magnetic pigments. In a psychophysical study, we assessed visual attractiveness of these coatings on a car-like shape for different viewing angles.
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    Neural Appearance Synthesis and Transfer
    (The Eurographics Association, 2019) Mazlov, Ilya; Merzbach, Sebastian; Trunz, Elena; Klein, Reinhard; Klein, Reinhard and Rushmeier, Holly
    Appearance acquisition is a challenging problem. Existing approaches require expensive hardware and acquisition times are long. Alternative ''in-the-wild'' few-shot approaches provide a limited reconstruction quality. Furthermore, there is a fundamental tradeoff between spatial resolution and the physical sample dimensions that can be captured in one measurement. In this paper, we investigate how neural texture synthesis and neural style transfer approaches can be applied to generate new materials with high spatial resolution from high quality SVBRDF measurements. We perform our experiments on a new database of measured SVBRDFs.
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    Estimating Homogeneous Data-driven BRDF Parameters from a Reflectance Map under Known Natural Lighting
    (The Eurographics Association, 2019) Cooper, Victoria L.; Bieron, James C.; Peers, Pieter; Klein, Reinhard and Rushmeier, Holly
    In this paper we demonstrate robust estimation of the model parameters of a fully-linear data-driven BRDF model from a reflectance map under known natural lighting. To regularize the estimation of the model parameters, we leverage the reflectance similarities within a material class. We approximate the space of homogeneous BRDFs using a Gaussian mixture model, and assign a material class to each Gaussian in the mixture model. Next, we compute a linear solution per material class. Finally, we select the best candidate as the final estimate. We demonstrate the efficacy and robustness of our method using the MERL BRDF database under a variety of natural lighting conditions.
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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.
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    Spectral Rendering with the Bounded MESE and sRGB Data
    (The Eurographics Association, 2019) Peters, Christoph; Merzbach, Sebastian; Hanika, Johannes; Dachsbacher, Carsten; Klein, Reinhard and Rushmeier, Holly
    In a recent journal paper, we introduced a technique to represent reflectance spectra by an arbitrary number of Fourier coefficients. As a special case, we converted tristimulus data to three Fourier coefficients. After summarizing this work, we introduce the Fourier sRGB color space. It is defined in terms of Fourier coefficients but designed to behave similar to sRGB. Textures stored in Fourier sRGB support efficient spectral rendering but can be compressed with techniques designed for sRGB textures. Compression errors are similar to sRGB.