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Item Geometry and Attribute Compression for Voxel Scenes(The Eurographics Association and John Wiley & Sons Ltd., 2016) Dado, Bas; Kol, Timothy R.; Bauszat, Pablo; Thiery, Jean-Marc; Eisemann, Elmar; Joaquim Jorge and Ming LinVoxel-based approaches are today's standard to encode volume data. Recently, directed acyclic graphs (DAGs) were successfully used for compressing sparse voxel scenes as well, but they are restricted to a single bit of (geometry) information per voxel. We present a method to compress arbitrary data, such as colors, normals, or reflectance information. By decoupling geometry and voxel data via a novel mapping scheme, we are able to apply the DAG principle to encode the topology, while using a palette-based compression for the voxel attributes, leading to a drastic memory reduction. Our method outperforms existing state-of-the-art techniques and is well-suited for GPU architectures. We achieve real-time performance on commodity hardware for colored scenes with up to 17 hierarchical levels (a 128K3 voxel resolution), which are stored fully in core.Item Compressed Multiresolution Hierarchies for High-Quality Precomputed Shadows(The Eurographics Association and John Wiley & Sons Ltd., 2016) Scandolo, Leonardo; Bauszat, Pablo; Eisemann, Elmar; Joaquim Jorge and Ming LinThe quality of shadow mapping is traditionally limited by texture resolution. We present a novel lossless compression scheme for high-resolution shadow maps based on precomputed multiresolution hierarchies. Traditional multiresolution trees can compactly represent homogeneous regions of shadow maps at coarser levels, but require many nodes for fine details. By conservatively adapting the depth map, we can significantly reduce the tree complexity. Our proposed method offers high compression rates, avoids quantization errors, exploits coherency along all data dimensions, and is well-suited for GPU architectures. Our approach can be applied for coherent shadow maps as well, enabling several applications, including high-quality soft shadows and dynamic lights moving on fixed-trajectories.Item An Interactive Information Visualization Approach to Physically-Based Rendering(The Eurographics Association, 2016) Simons, Gerard; Ament, Marco; Herholz, Sebastian; Dachsbacher, Carsten; Eisemann, Martin; Eisemann, Elmar; Matthias Hullin and Marc Stamminger and Tino WeinkaufIn this work, we present a novel information visualization tool to gain insight into the light transport in a physically-based rendering setting. The tool consists of a sampling-based data reduction technique, an extended interactive parallel coordinates plot providing an overview of the attributes linked to each light sample, 2D and 3D heat maps to represent different aspects of the rendering process, as well as a three-dimensional view to display and animate the light path transportation throughout the scene. We show several applications including differential light transport visualization for scene analysis, lighting and material optimization, reduction of rendering artifacts, and user-guided importance sampling.Item Merged Multiresolution Hierarchies for Shadow Map Compression(The Eurographics Association and John Wiley & Sons Ltd., 2016) Scandolo, Leonardo; Bauszat, Pablo; Eisemann, Elmar; Eitan Grinspun and Bernd Bickel and Yoshinori DobashiMultiresolution Hierarchies (MH) and Directed Acyclic Graphs (DAG) are two recent approaches for the compression of highresolution shadow information. In this paper, we introduce Merged Multiresolution Hierarchies (MMH), a novel data structure that unifies both concepts. An MMH leverages both hierarchical homogeneity exploited in MHs, as well as topological similarities exploited in DAG representations. We propose an efficient hash-based technique to quickly identify and remove redundant subtree instances in a modified relative MH representation. Our solution remains lossless and significantly improves the compression rate compared to both preceding shadow map compression algorithms, while retaining the full run-time performance of traditional MH representations.Item Hierarchical Stochastic Neighbor Embedding(The Eurographics Association and John Wiley & Sons Ltd., 2016) Pezzotti, Nicola; Höllt, Thomas; Lelieveldt, Boudewijn P. F.; Eisemann, Elmar; Vilanova, Anna; Kwan-Liu Ma and Giuseppe Santucci and Jarke van WijkIn recent years, dimensionality-reduction techniques have been developed and are widely used for hypothesis generation in Exploratory Data Analysis. However, these techniques are confronted with overcoming the trade-off between computation time and the quality of the provided dimensionality reduction. In this work, we address this limitation, by introducing Hierarchical Stochastic Neighbor Embedding (Hierarchical-SNE). Using a hierarchical representation of the data, we incorporate the wellknown mantra of Overview-First, Details-On-Demand in non-linear dimensionality reduction. First, the analysis shows an embedding, that reveals only the dominant structures in the data (Overview). Then, by selecting structures that are visible in the overview, the user can filter the data and drill down in the hierarchy. While the user descends into the hierarchy, detailed visualizations of the high-dimensional structures will lead to new insights. In this paper, we explain how Hierarchical-SNE scales to the analysis of big datasets. In addition, we show its application potential in the visualization of Deep-Learning architectures and the analysis of hyperspectral images.Item VarVis: Visualizing Anatomical Variation in Branching Structures(The Eurographics Association, 2016) Smit, Noeska; Kraima, Annelot; Jansma, Daniel; deRuiter, Marco; Eisemann, Elmar; Vilanova, Anna; Enrico Bertini and Niklas Elmqvist and Thomas WischgollAnatomical variations are naturally-occurring deviations from typical human anatomy. While these variations are considered normal and non-pathological, they are still of interest in clinical practice for medical specialists such as radiologists and transplantation surgeons. The complex variations in branching structures, for instance in arteries or nerves, are currently visualized side-by-side in illustrations or expressed using plain text in medical publications. In this work, we present a novel way of visualizing anatomical variations in complex branching structures for educational purposes: VarVis. VarVis consists of several linked views that reveal global and local similarities and differences in the variations. We propose a novel graph representation to provide an overview of the topological changes. Our solution involves a topological similarity measure, which allows the user to select variations at a global level based on their degree of similarity. After a selection is made, local topological differences can be interactively explored using illustrations and topology graphs. We also incorporate additional information regarding the probability of the various cases. Our solution has several advantages over traditional approaches, which we demonstrate in an evaluation.Item The Online Anatomical Human: Web-based Anatomy Education(The Eurographics Association, 2016) Smit, Noeska; Hofstede, Cees-Willem; Kraima, Annelot; Jansma, Daniel; deRuiter, Marco; Eisemann, Elmar; Vilanova, Anna; Beatriz Sousa Santos and Jean-Michel DischlerThe Online Anatomical Human (OAH) is a web-based viewer for studying anatomy. It is based on real human anatomy and incorporates medical image data in linked 2D and 3D views that students can freely interact with. Our application is the only to support 2D and 3D views based on real medical imaging data. The main goal of this anatomical online resource is to serve as an educational platform available to anyone with access to a modern web browser. Users can annotate regions, add comments, and provide hyperlinks to additional media. By making our work accessible to medical experts, we can ensure an increasing amount of information, leading to an evergrowing gain in educational value. The OAH will be used in an upcoming Massive Open Online Course (MOOC) to teach anatomy of the pelvis and will be made available to students worldwide via the web.Item Harvesting Dynamic 3D Worlds from Commodity Sensor Clouds(The Eurographics Association, 2016) Boubekeur, Tamy; Cignoni, Paolo; Eisemann, Elmar; Goesele, Michael; Klein, Reinhard; Roth, Stefan; Weinmann, Michael; Wimmer, Michael; Chiara Eva Catalano and Livio De LucaThe EU FP7 FET-Open project ''Harvest4D: Harvesting Dynamic 3D Worlds from Commodity Sensor Clouds'' deals with the acquisition, processing, and display of dynamic 3D data. Technological progress is offering us a wide-spread availability of sensing devices that deliver different data streams, which can be easily deployed in the real world and produce streams of sampled data with increased density and easier iteration of the sampling process. These data need to be processed and displayed in a new way. The Harvest4D project proposes a radical change in acquisition and processing technology: instead of a goaldriven acquisition that determines the devices and sensors, its methods let the sensors and resulting available data determine the acquisition process. A variety of challenging problems need to be solved: huge data amounts, different modalities, varying scales, dynamic, noisy and colorful data. This short contribution presents a selection of the many scientific results produced by Harvest4D. We will focus on those results that could bring a major impact to the Cultural Heritage domain, namely facilitating the acquisition of the sampled data or providing advanced visual analysis capabilities.Item Split-Depth Image Generation and Optimization(The Eurographics Association and John Wiley & Sons Ltd., 2016) Liao, Jingtang; Eisemann, Martin; Eisemann, Elmar; Jernej Barbic and Wen-Chieh Lin and Olga Sorkine-HornungSplit-depth images use an optical illusion, which can enhance the 3D impression of a 2D animation. In split-depth images (also often called split-depth GIFs due to the commonly used file format), static virtual occluders in form of vertical or horizontal bars are added to a video clip, which leads to occlusions that are interpreted by the observer as a depth cue. In this paper, we study different factors that contribute to the illusion and propose a solution to generate split-depth images for a given RGB + depth image sequence. The presented solution builds upon a motion summarization of the object of interest (OOI) through space and time. It allows us to formulate the bar positioning as an energy-minimization problem, which we solve efficiently. We take a variety of important features into account, such as the changes of the 3D effect due to changes in the motion topology, occlusion, the proximity of bars or the OOI, and scene saliency. We conducted a number of psycho-visual experiments to derive an appropriate energy formulation. Our method helps in finding optimal positions for the bars and, thus, improves the 3D perception of the original animation. We demonstrate the effectiveness of our approach on a variety of examples. Our study with novice users shows that our approach allows them to quickly create satisfying results even for complex animations.Item Efficient Ray Tracing Through Aspheric Lenses and Imperfect Bokeh Synthesis(The Eurographics Association and John Wiley & Sons Ltd., 2016) Joo, Hyuntae; Kwon, Soonhyeon; Lee, Sangmin; Eisemann, Elmar; Lee, Sungkil; Elmar Eisemann and Eugene FiumeWe present an efficient ray-tracing technique to render bokeh effects produced by parametric aspheric lenses. Contrary to conventional spherical lenses, aspheric lenses do generally not permit a simple closed-form solution of ray-surface intersections. We propose a numerical root-finding approach, which uses tight proxy surfaces to ensure a good initialization and convergence behavior. Additionally, we simulate mechanical imperfections resulting from the lens fabrication via a texture-based approach. Fractional Fourier transform and spectral dispersion add additional realism to the synthesized bokeh effect. Our approach is well-suited for execution on graphics processing units (GPUs) and we demonstrate complex defocus-blur and lens-flare effects.