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Now showing 1 - 10 of 91
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    Extracting Microfacet-based BRDF Parameters from Arbitrary Materials with Power Iterations
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Dupuy, Jonathan; Heitz, Eric; Iehl, Jean-Claude; Poulin, Pierre; Ostromoukhov, Victor; Jaakko Lehtinen and Derek Nowrouzezahrai
    We introduce a novel fitting procedure that takes as input an arbitrary material, possibly anisotropic, and automatically converts it to a microfacet BRDF. Our algorithm is based on the property that the distribution of microfacets may be retrieved by solving an eigenvector problem that is built solely from backscattering samples. We show that the eigenvector associated to the largest eigenvalue is always the only solution to this problem, and compute it using the power iteration method. This approach is straightforward to implement, much faster to compute, and considerably more robust than solutions based on nonlinear optimizations. In addition, we provide simple conversion procedures of our fits into both Beckmann and GGX roughness parameters, and discuss the advantages of microfacet slope space to make our fits editable. We apply our method to measured materials from two large databases that include anisotropic materials, and demonstrate the benefits of spatially varying roughness on texture mapped geometric models.
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    CoWRadar: Visual Quantification of the Circle of Willis in Stroke Patients
    (The Eurographics Association, 2015) Miao, Haichao; Mistelbauer, Gabriel; Našel, Christian; Gröller, M. Eduard; Katja Bühler and Lars Linsen and Nigel W. John
    This paper presents a method for the visual quantification of cerebral arteries, known as the Circle of Willis (CoW). The CoW is an arterial structure that is responsible for the brain's blood supply. Dysfunctions of this arterial circle can lead to strokes. The diagnosis relies on the radiologist's expertise and the software tools used. These tools consist of very basic display methods of the volumetric data without support of advanced technologies in medical image processing and visualization. The goal of this paper is to create an automated method for the standardized description of cerebral arteries in stroke patients in order to provide an overview of the CoW's configuration. This novel display provides visual indications of problematic areas as well as straightforward comparisons between multiple patients. Additionally, we offer a pipeline for extracting the CoW from Time-of-Flight Magnetic Resonance Angiography (TOF-MRA) data sets. An enumeration technique for the labeling of the arterial segments is therefore suggested. We also propose a method for detecting the CoW's main supplying arteries by analyzing the coronal, sagittal and transverse image planes of the data sets. We evaluated the feasibility of our visual quantification approach in a study of 63 TOF-MRA data sets and compared our findings to those of three radiologists. The obtained results demonstrate that our proposed techniques are effective in detecting the arteries of the CoW.
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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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    X-Dimensional Display: Superimposing 2D Cross-Sectional Image inside 3D Wireframe Aerial Image
    (The Eurographics Association, 2015) Furuyama, Yoshikazu; Makino, Yasutoshi; Shinoda, Hiroyuki; Masataka Imura and Pablo Figueroa and Betty Mohler
    In this paper, we propose a new interactive volumetric display which simultaneously shows a floating 3D image and its 2D cross sectional image inside it. This display enables users to see an arbitrary cross sectional image by inserting a hand-held semi-transparent screen into the 3D image floating in the mid-air. This system has following possibilities: doctors easily see MRI images inside the 3D body image, and designers check the internal structure of a 3D object in CAD. We construct a prototype device to demonstrate our proposed method by combining a 3D display and an aerial imaging technology. The spinning LED array constructs the volumetric image, and which is optically mirrored to appear in the free-space by the transmissive mirror called Aerial Imaging Plate (AIP). We find that a fine meshed silk screen can be inserted into the aerial image without disturbing the shape of it. Cross sectional images can be projected onto it together with the 3D image. We demonstrate how a silk screen diffuses a 3D aerial image and a projected 2D image.
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    Instant Visualization of Secondary Structures of Molecular Models
    (The Eurographics Association, 2015) Hermosilla, Pedro; Guallar, V.; Vinacua, Alvar; Vázquez, Pere-Pau; Katja Bühler and Lars Linsen and Nigel W. John
    Molecular Dynamics simulations are of key importance in the drug design field. Among all possible representations commonly used to inspect these simulations, Ribbons has the advantage of giving the expert a good overview of the conformation of the molecule. Although several techniques have been previously proposed to render ribbons, all of them have limitations in terms of space or calculation time, making them not suitable for real-time interaction with simulation software. In this paper we present a novel adaptive method that generates ribbons in real-time, taking advantage of the tessellation shader. The result is a fast method that requires no precomputation, and that generates high quality shapes and shading.
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    Surfel Octrees: A New Scheme for Interactive Inspection of Anatomy Atlases in Client-Server Applications
    (The Eurographics Association, 2015) Surinyac, Jordi; Brunet, Pere; Mateu Sbert and Jorge Lopez-Moreno
    Nowadays, an increasing interest on tele-medicine and tele-diagnostic solutions can be observed, with client/server architectures for remote inspection of volume image-based medical data which are becoming more and more popular. The use of portable devices is gradually spreading due to their portability and easy maintenance. In this paper, we present an efficient data model for segmented volume models based on a hierarchical data structure of surfels per anatomical structure. Surfel Octrees are compact enough for transmission through networks with limited bandwidth, and provide good visual quality in the client devices at a limited footprint. Anatomy atlases are represented as octree forests, supporting local interaction in the client device and selection of groups of medical organs. After presenting the octree generation and interaction algorithms, we present several examples and discuss the interest of the proposed approach in low-end devices such as mobiles and tablets.
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    Improved Sparse Seeding for 3D Electrostatic Field Lines
    (The Eurographics Association, 2015) Scharnowski, Katrin; Boblest, Sebastian; Ertl, Thomas; E. Bertini and J. Kennedy and E. Puppo
    We present an improved seeding strategy for sparse visualization of electrostatic fields. By analyzing the curvature of the field lines, we extract points of extremal field strength between charges of different sign and use them to seed field lines, which consequently connect the corresponding charges. The resulting sparse representation can be seen as an extension to classic vector field topology depicting properties otherwise hidden. Finally, by applying our method to a synthetic data set, we show its benefits over previously published work.
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    Visualizing High-Dimensional Data: Advances in the Past Decade
    (The Eurographics Association, 2015) Liu, Shusen; Maljovec, Dan; Wang, Bei; Bremer, Peer-Timo; Pascucci, Valerio; R. Borgo and F. Ganovelli and I. Viola
    Massive simulations and arrays of sensing devices, in combination with increasing computing resources, have generated large, complex, high-dimensional datasets used to study phenomena across numerous fields of study. Visualization plays an important role in exploring such datasets. We provide a comprehensive survey of advances in high-dimensional data visualization over the past 15 years. We aim at providing actionable guidance for data practitioners to navigate through a modular view of the recent advances, allowing the creation of new visualizations along the enriched information visualization pipeline and identifying future opportunities for visualization research.
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    Semi-Automatic Digital Epigraphy from Images with Normals
    (The Eurographics Association, 2015) Berkiten, Sema; Fan, Xinyi; Rusinkiewicz, Szymon; David Mould and Pierre Bénard
    We present a semi-automated system for converting photometric datasets (RGB images with normals) into geometry-aware non-photorealistic illustrations that obey the common conventions of epigraphy (black-and-white archaeological drawings of inscriptions). We focus on rock inscriptions formed by carving into or pecking out the rock surface: these are characteristically rough with shallow relief, making the problem very challenging for previous line drawing methods. Our system allows the user to easily outline the inscriptions on the rock surface, then segment out the inscriptions and create line drawings and shaded renderings in a variety of styles. We explore both constant-width and tilt-indicating lines, as well as locally shape-revealing shading. Our system produces more understandable illustrations than previous NPR techniques, successfully converting epigraphy from a manual and painstaking process into a user-guided semi-automatic process.
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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.