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Now showing 1 - 10 of 116
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    Recent Advances in Adaptive Sampling and Reconstruction for Monte Carlo Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zwicker, Matthias; Jarosz, Wojciech; Lehtinen, Jaakko; Moon, Bochang; Ramamoorthi, Ravi; Rousselle, Fabrice; Sen, Pradeep; Soler, Cyril; Yoon, Sungeui E.; K. Hormann and O. Staadt
    Monte Carlo integration is firmly established as the basis for most practical realistic image synthesis algorithms because of its flexibility and generality. However, the visual quality of rendered images often suffers from estimator variance, which appears as visually distracting noise. Adaptive sampling and reconstruction algorithms reduce variance by controlling the sampling density and aggregating samples in a reconstruction step, possibly over large image regions. In this paper we survey recent advances in this area. We distinguish between “a priori” methods that analyze the light transport equations and derive sampling rates and reconstruction filters from this analysis, and “a posteriori” methods that apply statistical techniques to sets of samples to drive the adaptive sampling and reconstruction process. They typically estimate the errors of several reconstruction filters, and select the best filter locally to minimize error. We discuss advantages and disadvantages of recent state-of-the-art techniques, and provide visual and quantitative comparisons. Some of these techniques are proving useful in real-world applications, and we aim to provide an overview for practitioners and researchers to assess these approaches. In addition, we discuss directions for potential further improvements.
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    Skeleton-Intrinsic Symmetrization of Shapes
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zheng, Qian; Hao, Zhuming; Huang, Hui; Xu, Kai; Zhang, Hao; Cohen-Or, Daniel; Chen, Baoquan; Olga Sorkine-Hornung and Michael Wimmer
    Enhancing the self-symmetry of a shape is of fundamental aesthetic virtue. In this paper, we are interested in recovering the aesthetics of intrinsic reflection symmetries, where an asymmetric shape is symmetrized while keeping its general pose and perceived dynamics. The key challenge to intrinsic symmetrization is that the input shape has only approximate reflection symmetries, possibly far from perfect. The main premise of our work is that curve skeletons provide a concise and effective shape abstraction for analyzing approximate intrinsic symmetries as well as symmetrization. By measuring intrinsic distances over a curve skeleton for symmetry analysis, symmetrizing the skeleton, and then propagating the symmetrization from skeleton to shape, our approach to shape symmetrization is skeleton-intrinsic. Specifically, given an input shape and an extracted curve skeleton, we introduce the notion of a backbone as the path in the skeleton graph about which a self-matching of the input shape is optimal. We define an objective function for the reflective self-matching and develop an algorithm based on genetic programming to solve the global search problem for the backbone. The extracted backbone then guides the symmetrization of the skeleton, which in turn, guides the symmetrization of the whole shape. We show numerous intrinsic symmetrization results of hand drawn sketches and artist-modeled or reconstructed 3D shapes, as well as several applications of skeleton-intrinsic symmetrization of shapes.
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    A Virtual and Augmented Reality Course Based on Inexpensive Interaction Devices and Displays
    (The Eurographics Association, 2015) Santos, Beatriz Sousa; Dias, Paulo; Madeira, Joaquim; M. Bronstein and M. Teschner
    In the last years a plethora of affordable displays, sensors, and interaction devices has reached the market, fostering the application of Virtual and Augmented Reality to many new situations. Yet, creating such applications requires a good understanding of the field and specific technical skills typically not provided by current Computer Science and Engineering education. This paper presents a graduate level course offered to MSc. Programs in Computer and Electrical Engineering which introduces the main concepts, techniques and tools in Virtual and Augmented Reality. The aim is to provide students with enough background to understand, design, implement and test such applications. The course organization, the main issues addressed and bibliography, the sensors, interaction devices and displays used, and a sample of the practical projects are briefly described. Major issues are discussed and conclusions are drawn.
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    Separation of Manga Line Drawings and Screentones
    (The Eurographics Association, 2015) Ito, Kota; Matsui, Yusuke; Yamasaki, Toshihiko; Aizawa, Kiyoharu; B. Bickel and T. Ritschel
    Screentones are unique expressions of Japanese comics (manga), which enrich their visual expression. However, such screentones have a very different visual nature from that of line drawing areas; this prevents us from applying various kinds of image processing techniques to manga. We propose a method for extracting line drawings and removing screentones. We employ Laplacians of Gaussian filters and flow-based differences of Gaussian filters, one for removing screentones and the other for preserving lines, and make a binary mask for separating line drawings from manga by merging the results of the two filters. We show that the proposed method successfully separates line drawings and is better than existing methods in comparative studies.
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    Guided Analysis of Cardiac 4D PC-MRI Blood Flow Data
    (The Eurographics Association, 2015) Köhler, Benjamin; Preim, Uta; Grothoff, Matthias; Gutberlet, Matthias; Fischbach, Katharina; Preim, Bernhard; H.-C. Hege and T. Ropinski
    Four-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) allows the non-invasive acquisition of temporally resolved, three-dimensional blood flow information. Quantitative and qualitative data analysis helps to assess the cardiac function, severity of diseases and find indications of different cardiovascular pathologies. However, various steps are necessary to achieve expressive visualizations and reliable results. This comprises the correction of special MR-related artifacts, the segmentation of vessels, flow integration with feature extraction and the robust quantification of clinically important measures. A fast and easy-to-use processing pipeline is essential since the target user group are physicians. We present a system that offers such a guided workflow for cardiac 4D PC-MRI data. The aorta and pulmonary artery can be analyzed within ten minutes including vortex extraction and robust determination of the stroke volume as well as the percentaged backflow. 64 datasets of healthy volunteers and of patients with variable diseases such as aneurysms, coarctations and insufficiencies were processed so far.
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    Self Tuning Texture Optimization
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kaspar, Alexandre; Neubert, Boris; Lischinski, Dani; Pauly, Mark; Kopf, Johannes; Olga Sorkine-Hornung and Michael Wimmer
    The goal of example-based texture synthesis methods is to generate arbitrarily large textures from limited exemplars in order to fit the exact dimensions and resolution required for a specific modeling task. The challenge is to faithfully capture all of the visual characteristics of the exemplar texture, without introducing obvious repetitions or unnatural looking visual elements. While existing non-parametric synthesis methods have made remarkable progress towards this goal, most such methods have been demonstrated only on relatively low-resolution exemplars. Real-world high resolution textures often contain texture details at multiple scales, which these methods have difficulty reproducing faithfully. In this work, we present a new general-purpose and fully automatic selftuning non-parametric texture synthesis method that extends Texture Optimization by introducing several key improvements that result in superior synthesis ability. Our method is able to self-tune its various parameters and weights and focuses on addressing three challenging aspects of texture synthesis: (i) irregular large scale structures are faithfully reproduced through the use of automatically generated and weighted guidance channels; (ii) repetition and smoothing of texture patches is avoided by new spatial uniformity constraints; (iii) a smart initialization strategy is used in order to improve the synthesis of regular and near-regular textures, without affecting textures that do not exhibit regularities. We demonstrate the versatility and robustness of our completely automatic approach on a variety of challenging high-resolution texture exemplars.
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    Real-time Content Adaptive Depth Retargeting for Light Field Displays
    (The Eurographics Association, 2015) Adhikarla, Vamsi Kiran; Marton, Fabio; Barsi, Attila; Kovács, Péter Tamás; Balogh, Tibor; Gobbetti, Enrico; B. Solenthaler and E. Puppo
    Light field display systems present visual scenes using a set of directional light beams emitted from multiple light sources as if they are emitted from points in a physical scene. These displays offer better angular resolution and therefore provide more depth of field than other automultiscopic displays. However in some cases the size of a scene may still exceed the available depth range of a light field display. Thus, rendering on these displays requires suitable adaptation of 3D content for providing comfortable viewing experience. We propose a content adaptive depth retargeting method to automatically modify the scene depth to suit to the needs of a light field display. By analyzing the scene and using display specific parameters, we formulate and solve an optimization problem to non-linearly adapt the scene depth to display depth. Our method synthesizes the depth retargeted light field content in real-time for supporting interactive visualization and also preserves the 3D appearance of the displayed objects as much as possible.
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    Augmented Reality as a Tool to Deliver e-Learning based Blended Content in and out of the Class-room
    (The Eurographics Association, 2015) Erdt, Marius; Maroothynaden, Jason; Peng, Junming; Müller-Wittig, Wolfgang; Gagnon, Paul; M. Bronstein and M. Teschner
    In this paper, we present a mobile Augmented Reality application that can be used for undergraduate anatomical education. It can be used in and out of the classroom. In the classroom, the application can track and augment 3D objects such as a cadaveric solid organ (e.g. heart) specimens as well as 3D plastic anatomical models without the use of observable markers. Out-side the classroom, virtual representations of the hearts were computed and added as an offline version to the application allowing students to self-learn. To allow students to ''sense-make'' concepts and add additional educational value to offline content, the application can also track 2D content like printed posters. Augmentation in 2D and 3D views via various digital content modalities supports students in learning and ''sense-making'' anatomical terms and concepts.
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    A Cut-Cell Geometric Multigrid Poisson Solver for Fluid Simulation
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Weber, Daniel; Mueller-Roemer, Johannes; Stork, André; Fellner, Dieter W.; Olga Sorkine-Hornung and Michael Wimmer
    We present a novel multigrid scheme based on a cut-cell formulation on regular staggered grids which generates compatible systems of linear equations on all levels of the multigrid hierarchy. This geometrically motivated formulation is derived from a finite volume approach and exhibits an improved rate of convergence compared to previous methods. Existing fluid solvers with voxelized domains can directly benefit from this approach by only modifying the representation of the non-fluid domain. The necessary building blocks are fully parallelizable and can therefore benefit from multi- and many-core architectures.
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    High-Order Recursive Filtering of Non-Uniformly Sampled Signals for Image and Video Processing
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Gastal, Eduardo S. L.; Oliveira, Manuel M.; Olga Sorkine-Hornung and Michael Wimmer
    We present a discrete-time mathematical formulation for applying recursive digital filters to non-uniformly sampled signals. Our solution presents several desirable features: it preserves the stability of the original filters; is well-conditioned for low-pass, high-pass, and band-pass filters alike; its cost is linear in the number of samples and is not affected by the size of the filter support. Our method is general and works with any non-uniformly sampled signal and any recursive digital filter defined by a difference equation. Since our formulation directly uses the filter coefficients, it works out-of-the-box with existing methodologies for digital filter design. We demonstrate the effectiveness of our approach by filtering non-uniformly sampled signals in various image and video processing tasks including edge-preserving color filtering, noise reduction, stylization, and detail enhancement. Our formulation enables, for the first time, edge-aware evaluation of any recursive infinite impulse response digital filter (not only low-pass), producing high-quality filtering results in real time.