MAM2016: Eurographics Workshop on Material Appearance Modeling

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https://diglib.eg.org/handle/10.2312/2630839

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Browsing MAM2016: Eurographics Workshop on Material Appearance Modeling by Title

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    Exploring Material Recognition for Estimating Reflectance and Illumination From a Single Image
    (The Eurographics Association, 2016) Weinmann, Michael; Klein, Reinhard; Reinhard Klein and Holly Rushmeier
    In this paper, we propose a novel approach for recovering illumination and reflectance from a single image. Our approach relies on the assumption that the surface geometry has already been reconstructed and a-priori knowledge in form of a database of digital material models is available. The first step of our technique consists in recognizing the respective material in the image using synthesized training data based on the given material database. Subsequently, the illumination conditions are estimated based on the recognized material and the surface geometry. Using this novel strategy we demonstrate that reflectance and illumination can be estimated reliably for several materials that are beyond simple Lambertian surface reflectance behavior because of exhibiting mesoscopic effects such as interreflections and shadows.
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    Gaze Analysis of BRDF Distortions
    (The Eurographics Association, 2016) Filip, J.; Havran, V.; Myszkowski, K.; Reinhard Klein and Holly Rushmeier
    BRDFs are currently used as a standard representation of material surface reflectance properties either in the from of tabulated measurements or a parametric model. However, the compression of tabulated representations as well as their fitting into such a parametric model typically introduces some visual degradations. We describe our analysis of the human gaze behavior in two types of standard visual experiments, where the common task is to compare a pair of BRDFs. The analysis was carried out across six different isotropic/anisotropic materials and three application-relevant BRDF degradation models.
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    Interactive Appearance Prediction for Cloudy Beverages
    (The Eurographics Association, 2016) Dal Corso, Alessandro; Frisvad, Jeppe Revall; Kjeldsen, Thomas Kim; Bærentzen, Jakob Andreas; Reinhard Klein and Holly Rushmeier
    Juice appearance is important to consumers, so digital juice with a slider that varies a production parameter or changes juice content is useful. It is however challenging to render juice with scattering particles quickly and accurately. As a case study, we create an appearance model that provides the optical properties needed for rendering of unfiltered apple juice. This is a scattering medium that requires volume path tracing as the scattering is too much for single scattering techniques and too little for subsurface scattering techniques. We investigate techniques to provide a progressive interactive appearance prediction tool for this type of medium. Our renderings are validated by qualitative and quantitative comparison with photographs. Visual comparisons using our interactive tool enable us to estimate the apple particle concentration of a photographed apple juice.
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    Isotropic BRDF Measurements with Quantified Uncertainties
    (The Eurographics Association, 2016) Hegedus, R.; Lucat, A.; Redon, J.; Pacanowski, R.; Reinhard Klein and Holly Rushmeier
    Image-based BRDF measurements on spherical material samples present a great opportunity to shorten significantly the acquisition time with respect to more traditional, non-multiplexed measurement methods for isotropic BRDFs. However, it has never been analyzed deeply, what measurement accuracy can be achieved in such a setup; what are the main contributing uncertainty factors and how do they relate to calibration procedures. In this paper we present a new set of isotropic BRDF measurements with their radiometric and geometric uncertainties acquired within such an imaging setup.We discuss the most prominent optical phenomena that a ect measurement accuracy and pave the way for more thorough uncertainty analysis in forthcoming image-based BRDF measurements. Our newly acquired data with their quantified uncertainties will be helpful for comparing the quality and accuracy of the di erent experimental setups and for designing other such image-based BRDF measurement devices.
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    MAM 2016: Frontmatter
    (Eurographics Association, 2016) Reinhard Klein; Holly Rushmeier;
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    Practical Experiences with Using Autocollimator for Surface Reflectance Measurement
    (The Eurographics Association, 2016) Havran, Vlastimil; Reinhard Klein and Holly Rushmeier
    We present our experiences with using an autocollimator to set up the surface reflectance measurement for both BRDF and BTF. Assuming the measured material appearance is put on a locally flat surface, the autocollimator allows us to set the perpendicularity of the measured sample in stationary measurement setups. The principle works also vice versa, we can align the measurement setup against a stationary sample for on-site measurements. The autocollimator requires to use a collimated beam of light, a mirror, a beam splitter, and a detector. We describe the autocollimator principle, problems, and the issues involved when using an autocollimator for surface reflectance measurement setups.
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    Sparse Sampling for Image-Based SVBRDF Acquisition
    (The Eurographics Association, 2016) Yu, Jiyang; Xu, Zexiang; Mannino, Matteo; Jensen, Henrik Wann; Ramamoorthi, Ravi; Reinhard Klein and Holly Rushmeier
    We acquire the data-driven spatially-varying (SV)BRDF of a flat sample from only a small number of images (typically 20). We generalize the homogenous BRDF acquisition work of Nielsen et al., who derived an optimal minmal set of lighting/view directions, treating a 4 degree-of-freedom spherical gantry as a gonioreflectometer. In contrast, we benefit from using the full 2D camera image from the gantry to enable SVBRDF acquisition. Like Nielsen et al, our method is data-driven, based on the MERL database of isotropic BRDFs, and finds the optimal directions by minimizing the condition number of the acquisition matrix. We extend their approach to SVBRDFs by modifying the optimal incident/outgoing directions to avoid grazing angles that reduce resolution and make alignment of different views difficult. Another key practical issue is aligning multiple viewpoints, and correcting for near-field effects. We demonstrate our method on SVBRDF measurements of new flat materials, showing that full data-driven SVBRDF acquisition is now possible from a sparse set of only about 20 light-view pairs.
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    Weathering of Urban Scenes: Challenges and Possible Solutions
    (The Eurographics Association, 2016) Muñoz-Pandiella, I.; Bosch, C.; Mérillou, N.; Pueyo, X.; Mérillou, S; Patow, G.; Reinhard Klein and Holly Rushmeier
    In this paper, we propose to discuss on one of the main challenges in realistic rendering of urban scenes: changes in appearance over time within a urban context. After studying the previous work on weathering techniques, we have found that there is a lack of estimation for some important environmental parameters (such as sun radiation) that have a wrong impact on weathering phenomena simulation and, thus, on the appearance of virtual objects. We also think that such a problem needs to be addressed on large urban models. Here, we discuss some possible solutions we have studied in our research. These solutions are focused on screen-space techniques, in order to efficiently compute those factors and use them to interactively generate weathering effects.