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Item Microtiles: Extracting Building Blocks from Correspondences(The Eurographics Association and Blackwell Publishing Ltd., 2012) Kalojanov, Javor; Bokeloh, Martin; Wand, Michael; Guibas, Leonidas; Seidel, Hans-Peter; Slusallek, Philipp; Eitan Grinspun and Niloy MitraIn this paper, we develop a theoretical framework for characterizing shapes by building blocks. We address two questions: First, how do shape correspondences induce building blocks? For this, we introduce a new representation for structuring partial symmetries (partial self-correspondences), which we call "microtiles". Starting from input correspondences that form point-wise equivalence relations, microtiles are obtained by grouping connected components of points that share the same set of symmetry transformations. The decomposition is unique, requires no parameters beyond the input correspondences, and encodes the partial symmetries of all subsets of the input. The second question is: What is the class of shapes that can be assembled from these building blocks? Here, we specifically consider r-similarity as correspondence model, i.e., matching of local r-neighborhoods. Our main result is that the microtiles of the partial r-symmetries of an object S can build all objects that are (r+e)-similar to S for any e>0. Again, the construction is unique. Furthermore, we give necessary conditions for a set of assembly rules for the pairwise connection of tiles. We describe a practical algorithm for computing microtile decompositions under rigid motions, a corresponding prototype implementation, and conduct a number of experiments to visualize the structural properties in practice.Item Optimizing Disparity for Motion in Depth(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kellnhofer, Petr; Ritschel, Tobias; Myszkowski, Karol; Seidel, Hans-Peter; Nicolas Holzschuch and Szymon RusinkiewiczBeyond the careful design of stereo acquisition equipment and rendering algorithms, disparity post-processing has recently received much attention, where one of the key tasks is to compress the originally large disparity range to avoid viewing discomfort. The perception of dynamic stereo content however, relies on reproducing the full disparity-time volume that a scene point undergoes in motion. This volume can be strongly distorted in manipulation, which is only concerned with changing disparity at one instant in time, even if the temporal coherence of that change is maintained. We propose an optimization to preserve stereo motion of content that was subject to an arbitrary disparity manipulation, based on a perceptual model of temporal disparity changes. Furthermore, we introduce a novel 3D warping technique to create stereo image pairs that conform to this optimized disparity map. The paper concludes with perceptual studies of motion reproduction quality and task performance in a simple game, showing how our optimization can achieve both viewing comfort and faithful stereo motion.Item Pattern Search in Flows based on Similarity of Stream Line Segments(The Eurographics Association, 2014) Wang, Zhongjie; Esturo, Janick Martinez; Seidel, Hans-Peter; Weinkauf, Tino; Jan Bender and Arjan Kuijper and Tatiana von Landesberger and Holger Theisel and Philipp UrbanWe propose a method that allows users to define flow features in form of patterns represented as sparse sets of stream line segments. Our approach finds ''similar'' occurrences in the same or other time steps. Related approaches define patterns using dense, local stencils or support only single segments. Our patterns are defined sparsely and can have a significant extent, i.e., they are integration-based and not local. This allows for a greater flexibility in defining features of interest. Similarity is measured using intrinsic curve properties only, which enables invariance to location, orientation, and scale. Our method starts with splitting stream lines using globally-consistent segmentation criteria. It strives to maintain the visually apparent features of the flow as a collection of stream line segments. Most importantly, it provides similar segmentations for similar flow structures. For user-defined patterns of curve segments, our algorithm finds similar ones that are invariant to similarity transformations. We showcase the utility of our method using different 2D and 3D flow fields.Item Interactive Motion Mapping for Real-time Character Control(The Eurographics Association and John Wiley and Sons Ltd., 2014) Rhodin, Helge; Tompkin, James; Kim, Kwang In; Varanasi, Kiran; Seidel, Hans-Peter; Theobalt, Christian; B. Levy and J. KautzAbstract It is now possible to capture the 3D motion of the human body on consumer hardware and to puppet in real time skeleton-based virtual characters. However, many characters do not have humanoid skeletons. Characters such as spiders and caterpillars do not have boned skeletons at all, and these characters have very different shapes and motions. In general, character control under arbitrary shape and motion transformations is unsolved - how might these motions be mapped? We control characters with a method which avoids the rigging-skinning pipeline - source and target characters do not have skeletons or rigs. We use interactively-defined sparse pose correspondences to learn a mapping between arbitrary 3D point source sequences and mesh target sequences. Then, we puppet the target character in real time. We demonstrate the versatility of our method through results on diverse virtual characters with different input motion controllers. Our method provides a fast, flexible, and intuitive interface for arbitrary motion mapping which provides new ways to control characters for real-time animation.Item Virtual Passepartouts(The Eurographics Association, 2012) Ritschel, Tobias; Templin, Krzysztof; Myszkowski, Karol; Seidel, Hans-Peter; Paul Asente and Cindy GrimmIn traditional media, such as photography and painting, a cardboard sheet with a cutout (called passepartout) is frequently placed on top of an image. One of its functions is to increase the depth impression via the ''looking-through-a-window'' metaphor. This paper shows how an improved 3D effect can be achieved by using a virtual passepartout: a 2D framing that selectively masks the 3D shape and leads to additional occlusion events between the virtual world and the frame. We introduce a pipeline to design virtual passepartouts interactively as a simple post-process on RGB images augmented with depth information. Additionally, an automated approach finds the optimal virtual passepartout for a given scene. Virtual passepartouts can be used to enhance depth depiction in images and videos with depth information, renderings, stereo images and the fabrication of physical passepartoutsItem Partial Symmetry Detection in Volume Data(The Eurographics Association, 2011) Kerber, Jens; Wand, Michael; Krüger, Jens; Seidel, Hans-Peter; Peter Eisert and Joachim Hornegger and Konrad PolthierIn this paper, we present an algorithm for detecting partial Euclidean symmetries in volume data. Our algorithm finds subsets in voxel data that map to each other approximately under translations, rotations, and reflections. We implement the search for partial symmetries efficiently and robustly using a feature-based approach: We first reduce the volume to salient line features and then create transformation candidates from matching only local configurations of these line networks. Afterwards, only a shortlist of transformation candidates need to be verified using expensive dense volume matching. We apply our technique on both synthetic test scenes as well as real CT scans and show that we can recover a large amount of partial symmetries for complexly structured volume data sets.Item Dynamic Display of BRDFs(The Eurographics Association and Blackwell Publishing Ltd., 2011) Hullin, Matthias B.; Lensch, Hendrik P. A.; Raskar, Ramesh; Seidel, Hans-Peter; Ihrke, Ivo; M. Chen and O. DeussenThis paper deals with the challenge of physically displaying reflectance, i.e., the appearance of a surface and its variation with the observer position and the illuminating environment. This is commonly described by the bidirectional reflectance distribution function (BRDF). We provide a catalogue of criteria for the display of BRDFs, and sketch a few orthogonal approaches to solving the problem in an optically passive way. Our specific implementation is based on a liquid surface, on which we excite waves in order to achieve a varying degree of anisotropic roughness. The resulting probability density function of the surface normal is shown to follow a Gaussian distribution similar to most established BRDF models.Item Real-time Reflective and Refractive Novel-view Synthesis(The Eurographics Association, 2014) Lochmann, Gerrit; Reinert, Bernhard; Ritschel, Tobias; Müller, Stefan; Seidel, Hans-Peter; Jan Bender and Arjan Kuijper and Tatiana von Landesberger and Holger Theisel and Philipp UrbanWe extend novel-view image synthesis from the common diffuse and opaque image formation model to the reflective and refractive case. Our approach uses a ray tree of RGBZ images, where each node contains one RGB light path which is to be warped differently depending on the depth Z and the type of path. Core of our approach are two efficient procedures for reflective and refractive warping. Different from the diffuse and opaque case, no simple direct solution exists for general geometry. Instead, a per-pixel optimization in combination with informed initial guesses warps an HD image with reflections and refractions in 18 ms on a current mobile GPU. The key application is latency avoidance in remote rendering in particular for head-mounted displays. Other applications are single-pass stereo or multi-view, motion blur and depth-of-field rendering as well as their combinations.Item Deep Shading: Convolutional Neural Networks for Screen Space Shading(The Eurographics Association and John Wiley & Sons Ltd., 2017) Nalbach, Oliver; Arabadzhiyska, Elena; Mehta, Dushyant; Seidel, Hans-Peter; Ritschel, Tobias; Zwicker, Matthias and Sander, PedroIn computer vision, convolutional neural networks (CNNs) achieve unprecedented performance for inverse problems where RGB pixel appearance is mapped to attributes such as positions, normals or reflectance. In computer graphics, screen space shading has boosted the quality of real-time rendering, converting the same kind of attributes of a virtual scene back to appearance, enabling effects like ambient occlusion, indirect light, scattering and many more. In this paper we consider the diagonal problem: synthesizing appearance from given per-pixel attributes using a CNN. The resulting Deep Shading renders screen space effects at competitive quality and speed while not being programmed by human experts but learned from example images.Item Efficient Multi-image Correspondences for On-line Light Field Video Processing(The Eurographics Association and John Wiley & Sons Ltd., 2016) Dąbała, Łukasz; Ziegler, Matthias; Didyk, Piotr; Zilly, Frederik; Keinert, Joachim; Myszkowski, Karol; Seidel, Hans-Peter; Rokita, Przemysław; Ritschel, Tobias; Eitan Grinspun and Bernd Bickel and Yoshinori DobashiLight field videos express the entire visual information of an animated scene, but their shear size typically makes capture, processing and display an off-line process, i. e., time between initial capture and final display is far from real-time. In this paper we propose a solution for one of the key bottlenecks in such a processing pipeline, which is a reliable depth reconstruction possibly for many views. This is enabled by a novel correspondence algorithm converting the video streams from a sparse array of off-the-shelf cameras into an array of animated depth maps. The algorithm is based on a generalization of the classic multi-resolution Lucas-Kanade correspondence algorithm from a pair of images to an entire array. Special inter-image confidence consolidation allows recovery from unreliable matching in some locations and some views. It can be implemented efficiently in massively parallel hardware, allowing for interactive computations. The resulting depth quality as well as the computation performance compares favorably to other state-of-the art light field-to-depth approaches, as well as stereo matching techniques. Another outcome of this work is a data set of light field videos that are captured with multiple variants of sparse camera arrays.