Browsing by Author "Golla, Tim"

Now showing 1 - 3 of 3
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    Interactive Interpolation of Metallic Effect Car Paints
    (The Eurographics Association, 2018) Golla, Tim; Klein, Reinhard; Beck, Fabian and Dachsbacher, Carsten and Sadlo, Filip
    Metallic car paints are visually complex materials that, among others effects, exhibit a view-dependent metallic sparkling, which is particularly difficult to recreate in computer graphics. While capturing real-world metallic paints is possible with specialized devices, creating these materials computationally poses a difficult problem. We present a method that allows for interactive interpolation between measured metallic automotive paints, which can be used to generate new realistic-looking metallic paint materials. By clustering the color information present in the measured bidirectional texture function (BTF) responsible for the metallic sparkling effect, we set up an optimal transport problem between metallic paints' appearances. The design of the problem facilitates efficiently finding a solution, based on which we generate a representation that allows for real-time generation of interpolated realistic materials. Interpolation happens smoothly, no flickering or other visual artifacts can be observed. The developed approach also enables to separately interpolate the larger-scale reflective properties, including the basic color hue, the local color hue, and the sparkling intensity of the metallic paint. Our method can be used intuitively in order to generate automotive paints with a novel appearance and explore the space of possible metallic paints spanned by given real-world measurements. The resulting materials are also well suited for real-time rendering in standard engines.
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    Real-time Image-based Lighting of Microfacet BRDFs with Varying Iridescence
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Kneiphof, Tom; Golla, Tim; Klein, Reinhard; Boubekeur, Tamy and Sen, Pradeep
    Iridescence is a natural phenomenon that is perceived as gradual color changes, depending on the view and illumination direction. Prominent examples are the colors seen in oil films and soap bubbles. Unfortunately, iridescent effects are particularly difficult to recreate in real-time computer graphics. We present a high-quality real-time method for rendering iridescent effects under image-based lighting. Previous methods model dielectric thin-films of varying thickness on top of an arbitrary micro-facet model with a conducting or dielectric base material, and evaluate the resulting reflectance term, responsible for the iridescent effects, only for a single direction when using real-time image-based lighting. This leads to bright halos at grazing angles and over-saturated colors on rough surfaces, which causes an unnatural appearance that is not observed in ground truth data. We address this problem by taking the distribution of light directions, given by the environment map and surface roughness, into account when evaluating the reflectance term. In particular, our approach prefilters the first and second moments of the light direction, which are used to evaluate a filtered version of the reflectance term. We show that the visual quality of our approach is superior to the ones previously achieved, while having only a small negative impact on performance.
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    Temporal Upsampling of Point Cloud Sequences by Optimal Transport for Plant Growth Visualization
    (© 2020 Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd, 2020) Golla, Tim; Kneiphof, Tom; Kuhlmann, Heiner; Weinmann, Michael; Klein, Reinhard; Benes, Bedrich and Hauser, Helwig
    Plant growth visualization from a series of 3D scanner measurements is a challenging task. Time intervals between successive measurements are typically too large to allow a smooth animation of the growth process. Therefore, obtaining a smooth animation of the plant growth process requires a temporal upsampling of the point cloud sequence in order to obtain approximations of the intermediate states between successive measurements. Additionally, there are suddenly arising structural changes due to the occurrence of new plant parts such as new branches or leaves. We present a novel method that addresses these challenges via semantic segmentation and the generation of a segment hierarchy per scan, the matching of the hierarchical representations of successive scans and the segment‐wise computation of optimal transport. The transport problems' solutions yield the information required for a realistic temporal upsampling, which is generated in real time. Thereby, our method does not require shape templates, good correspondences or huge databases of examples. Newly grown and decayed parts of the plant are detected as unmatched segments and are handled by identifying corresponding bifurcation points and introducing virtual segments in the previous, respectively successive time step. Our method allows the generation of realistic upsampled growth animations with moderate computational effort.