MAM2015: Eurographics Workshop on Material Appearance Modeling: Issues and Acquisition

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    Quality Assurance Based on Descriptive and Parsimonious Appearance Models
    (The Eurographics Association, 2015) Nielsen, J. B.; Eiriksson, E. R.; Kristensen, R. L.; Wilm, J.; Frisvad, J. R.; Conradsen, K.; Aanæs, H.; Reinhard Klein and Holly Rushmeier
    In this positional paper, we discuss the potential benefits of using appearance models in additive manufacturing, metal casting, wind turbine blade production, and 3D content acquisition. Current state of the art in acquisition and rendering of appearance cannot easily be used for quality assurance in these areas. The common denominator is the need for descriptive and parsimonious appearance models. By 'parsimonious' we mean with few parameters so that a model is useful both for fast acquisition, robust fitting, and fast rendering of appearance. The word 'descriptive' refers to the fact that a model should represent the main features of the acquired appearance data. The solution we propose is to reduce the degrees of freedom by greater use of multivariate statistics.
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    Frontmatter: Eurographics 2015 Workshop on Material Appearance Modeling
    (The Eurographics Association, 2015) Klein, Reinhard; Rushmeier, Holly; -
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    A Short Survey on Optical Material Recognition
    (The Eurographics Association, 2015) Weinmann, M.; Klein, R.; Reinhard Klein and Holly Rushmeier
    The complexity of visual material appearance as observed in the huge variation in material appearance under different viewing and illumination conditions makes material recognition a highly challenging task. In the scope of this paper, we discuss the facts that make material appearance that complex and provide a survey on technical achievements towards a reliable material recognition that have been presented in the literature so far. In addition, we discuss still open challenges that might be in the focus of future research.
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    Proposal for an Appearance Exchange Format
    (The Eurographics Association, 2015) Mueller, Gero; Lamy, Francis; Reinhard Klein and Holly Rushmeier
    In this short paper X-Rite proposes a new file format for exchanging digital material appearance. The format is a vital part of X-Rite's appearance initiative consisting of a new generation of appearance capturing devices currently under development. In order to make the usage of measured appearance as simple as possible for users, a broad support by software vendors is essential. Therefore, X-Rite aims to initiate the assembly of a consortium of hard- and software vendors, members of the scientific community and users, which would be responsible for the further development and standardization of the format.
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    The Material Definition Language
    (The Eurographics Association, 2015) Kettner, L.; Raab, M.; Seibert, D.; Jordan, J.; Keller, A.; Reinhard Klein and Holly Rushmeier
    We introduce the physically-based Material Definition Language (MDL). Based on the principle of strictly separating material definition and rendering algorithms, each MDL material is applicable across different rendering paradigms ranging from realtime over interactive solutions to advanced light transport simulation.
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    Linear Models for Material BTFs and Possible Applications
    (The Eurographics Association, 2015) Brok, D. den; Weinmann, M.; Klein, R.; Reinhard Klein and Holly Rushmeier
    Due to the richness of real-world materials, arguably one of the biggest challenges in rendering is to come up with models that describe their appearance well. The image-based bidirectional texture function (BTF) is known to be able to model many effects that are hard or impossible to reproduce with analytical reflectance models. This advantage comes at the price of demanding storage and acquisition requirements. In previous work, we have demonstrated that these requirements can be lifted to some extent by means of data-driven linear models. We give a more in-depth overview on our research on such models and summarize the applications we investigated so far, followed by an outlook on what might yet be achievable.
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    Identifying Diffraction Effects in Measured Reflectances
    (The Eurographics Association, 2015) Holzschuch, N.; Pacanowski, R.; Reinhard Klein and Holly Rushmeier
    There are two different physical models connecting the micro-geometry of a surface and its physical reflectance properties (BRDF). The first, Cook-Torrance, assumes geometrical optics: light is reflected and masked by the micro-facets. In this model, the BRDF depends on the probability distribution of micro-facets normals. The second, Church-Takacs, assumes diffraction by the micro-geometry. In this model, the BRDF depends on the power spectral distribution of the surface height. Measured reflectance have been fitted to either model but results are not entirely satisfying. In this paper, we assume that both models are valid in BRDFs, but correspond to different areas in parametric space. We present a simple test to classify, locally, parts of the BRDF into the Cook-Torrance model or the diffraction model. The separation makes it easier to fit models to measured BRDFs.
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    In Praise of an Alternative BRDF Parametrization
    (The Eurographics Association, 2015) Barla, P.; Belcour, L.; Pacanowski, R.; Reinhard Klein and Holly Rushmeier
    In this paper, we extend the work of Neumann et al. [NNSK99] and Stark et al. [SAS05] to a pair of 4D BRDF parameterizations with explicit changes of variables. We detail their mathematical properties and relationships to the commonly-used halfway/difference parametrization, and discuss their benefits and drawbacks using a few analytical test functions and measured BRDFs. Our preliminary study suggests that the alternative parametrization inspired by Stark et al. [SAS05] is superior, and should thus be considered in future work involving BRDFs.
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    Geometric Accuracy Analysis of Stationary BTF Gonioreflectometers
    (The Eurographics Association, 2015) Havran, V.; Reinhard Klein and Holly Rushmeier
    The accurate BTF data representation requires specialized measurement gantries, some of them designed as gonireflectometers. These consist of an illumination source and a camera mounted on two robotic arms, one degree of freedom possibly achieved by rotation stage which a measured sample is mounted on. While there are several variations of the gonioreflectometer gantry, the principle of all remains the same, positioning directly the illumination and detector on a hemispherical surface over a sample. We analyze the positioning error of such gonioreflectometers. The input parameters are the required spatial resolution of a BTF sample and the distance between the camera used as a detector and the BTF sample. Our analysis confirms that the requirements for mechatronic actuators for the positioning of the sample and arms are very high and near the limit of state of the art technology.