Browsing by Author "Klein, Reinhard"
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Item Frontmatter: Eurographics 2018 Workshop on Material Appearance Modeling(The Eurographics Association, 2018) Klein, Reinhard; Rushmeier, Holly; Reinhard Klein and Holly RushmeierItem Hierarchical Additive Poisson Disk Sampling(The Eurographics Association, 2018) Dieckmann, Alexander; Klein, Reinhard; Beck, Fabian and Dachsbacher, Carsten and Sadlo, FilipGenerating samples of point clouds and meshes with blue noise characteristics is desirable for many applications in rendering and geometry processing. Working with laser-scanned or lidar point clouds, we usually find region with artifacts called scanlines and scan-edges. These regions are problematic for geometry processing applications, since it is not clear how many points should be selected to define a proper neighborhood. We present a method to construct a hierarchical additive poisson disk sampling from densely sampled point sets, which yield better point neighborhoods. It can be easily implemented using an octree data structure where each octree node contains a grid, called Modifiable Nested Octree [Sch14]. The generation of the sampling amounts to distributing the points over a hierarchy (octree) of resolution levels (grids) in a greedy manner. Propagating the distance constraint r through the hierarchy while drawing samples from the point set leads to a hierarchy of well distributed, random samplings. This ensures that in a disk with radius r, around a point, no other point upwards in the hierarchy is found. The sampling is additive in the sense that the union of points sets up to a certain hierarchy depth D is a poisson disk sampling. This makes it easy to select a resolution where the scan-artifacts have a lower impact on the processing result. The generated sampling can be made sensitive to surface features by a simple preprocessing step, yielding high quality low resolution poisson samplings of point clouds.Item Interactive Interpolation of Metallic Effect Car Paints(The Eurographics Association, 2018) Golla, Tim; Klein, Reinhard; Beck, Fabian and Dachsbacher, Carsten and Sadlo, FilipMetallic 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.Item MAM 2019: Frontmatter(Eurographics Association, 2019) Klein, Reinhard; Rushmeier, Holly; Klein, Reinhard and Rushmeier, HollyItem Neural Appearance Synthesis and Transfer(The Eurographics Association, 2019) Mazlov, Ilya; Merzbach, Sebastian; Trunz, Elena; Klein, Reinhard; Klein, Reinhard and Rushmeier, HollyAppearance 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.Item 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, PradeepIridescence 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.Item 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, HelwigPlant 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.Item VMV 2017 - Vision, Modeling and Visualization: Frontmatter(Eurographics Association, 2017) Hullin, Matthias; Klein, Reinhard; Schultz, Thomas; Yao, Angela; Matthias Hullin and Reinhard Klein and Thomas Schultz and Angela Yao