Volume 25 (2006)

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    Third Eurographics Symposium on Geometry Processing (in cooperation with ACM SIGGRAPH)
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Desbrun, Mathieu
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    Volume-Surface Trees
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Boubekeur, Tamy; Heidrich, Wolfgang; Granier, Xavier; Schlick, Christophe
    Many algorithms in computer graphics improve their efficiency by using Hierarchical Space Subdivision Schemes (HS3), such as octrees, kD-trees or BSP trees. Such HS3 usually provide an axis-aligned subdivision of the 3D space embedding a scene or an object. However, the purely volume-based behavior of these schemes often leads to strongly imbalanced surface clustering. In this article, we introduce the VS-Tree, an alternative HS3 providing efficient and accurate surface-based hierarchical clustering via a combination of a global 3D decomposition at coarse subdivision levels, and a local 2D decomposition at fine levels near the surface. First, we show how to efficiently construct VS-Trees over meshes and point-based surfaces, and analyze the improvement it offers for cluster-based surface simplification methods. Then we propose a new surface reconstruction algorithm based on the volume-surface classification of the VS-Tree. This new algorithm is faster than state-of-the-art reconstruction methods and provides a final semi-regular mesh comparable to the output of remeshing algorithms.
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    Optimizing Control Variate Estimators for Rendering
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Fan, Shaohua; Chenney, Stephen; Hu, Bo; Tsui, Kam-Wah; Lai, Yu-chi
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    Latent Doodle Space
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Baxter, William; Anjyo, Ken-ichi
    We propose the concept of a latent doodle space, a low-dimensional space derived from a set of input doodles, or simple line drawings. The latent space provides a foundation for generating new drawings that are similar, but not identical to, the input examples. The two key components of this technique are 1) a heuristic algorithm for finding stroke correspondences between the drawings, and 2) the use of latent variable methods to automatically extract a low-dimensional latent doodle space from the inputs. We present two practical applications that demonstrate the utility of this idea: first, a randomized stamp tool that creates a different image on every usage; and second, personalized probabilistic fonts, a handwriting synthesis technique that mimics the idiosyncrasies of one s own handwriting.Keywords: sketch, by-example, style learning, scattered data interpolation, principal component analysis, radial basis functions, Gaussian processes, digital in-betweening, handwriting synthesis
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    AFRIGRAPH: Computer Graphics in Africa
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Gain, J. E.; Strasser, W.
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    Guest Editorial: Selected Papers from the 18th Brazilian Symposium on Computer Graphics and Image Processing (SIBGRAPI 2005)
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Andreia, Maria; Rodrigues, Formico
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    Computing discrete shape operators on general meshes
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Grinspun, Eitan; Gingold, Yotam; Reisman, Jason; Zorin, Denis
    Discrete curvature and shape operators, which capture complete information about directional curvatures at a point, are essential in a variety of applications: simulation of deformable two-dimensional objects, variational modeling and geometric data processing. In many of these applications, objects are represented by meshes. Currently, a spectrum of approaches for formulating curvature operators for meshes exists, ranging from highly accurate but computationally expensive methods used in engineering applications to efficient but less accurate techniques popular in simulation for computer graphics.We propose a simple and efficient formulation for the shape operator for variational problems on general meshes, using degrees of freedom associated with normals. On the one hand, it is similar in its simplicity to some of the discrete curvature operators commonly used in graphics; on the other hand, it passes a number of important convergence tests and produces consistent results for different types of meshes and mesh refinement.
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    Competing Fronts for Coarse-to-Fine Surface Reconstruction
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Sharf, Andrei; Lewiner, Thomas; Shamir, Ariel; Kobbelt, Leif; Cohen-Or, Daniel
    We present a deformable model to reconstruct a surface from a point cloud. The model is based on an explicit mesh representation composed of multiple competing evolving fronts. These fronts adapt to the local feature size of the target shape in a coarse-to-fine manner. Hence, they approach towards the finer (local) features of the target shape only after the reconstruction of the coarse (global) features has been completed. This conservative approach leads to a better control and interpretation of the reconstructed topology. The use of an explicit representation for the deformable model guarantees water-tightness and simple tracking of topological events. Furthermore, the coarse-to-fine nature of reconstruction enables adaptive handling of non-homogenous sample density, including robustness to missing data in defected areas.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Digitizing and scanning.Keywords: surface reconstruction, deformable models
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    Cache-Efficient Layouts of Bounding Volume Hierarchies
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Yoon, Sung-Eui; Manocha, Dinesh
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    Easy Matting - A Stroke Based Approach for Continuous Image Matting
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Guan, Yu; Chen, Wei; Liang, Xiao; Ding, Ziang; Peng, Qunsheng
    We propose an iterative energy minimization framework for interactive image matting. Our approach is easy in the sense that it is fast and requires only few user-specified strokes for marking the foreground and background. Beginning with the known region, we model the unknown region as a Markov Random Field (MRF) and formulate its energy in each iteration as the combination of one data term and one smoothness term. By automatically adjusting the weights of both terms during the iterations, the first-order continuous and feature-preserving result is rapidly obtained with several iterations. The energy optimization can be further performed in selected local regions for refined results. We demonstrate that our energy-driven scheme can be extended to video matting, with which the spatio-temporal smoothness is faithfully preserved. We show that the proposed approach outperforms previous methods in terms of both the quality and performance for quite challenging examples.
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    Real-Time Weighted Pose-Space Deformation on the GPU
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Rhee, Taehyun; Lewis, J.P.; Neumann, Ulrich
    WPSD (Weighted Pose Space Deformation) is an example based skinning method for articulated body animation. The per-vertex computation required in WPSD can be parallelized in a SIMD (Single Instruction Multiple Data) manner and implemented on a GPU. While such vertex-parallel computation is often done on the GPU vertex processors, further parallelism can potentially be obtained by using the fragment processors. In this paper, we develop a parallel deformation method using the GPU fragment processors. Joint weights for each vertex are automatically calculated from sample poses, thereby reducing manual effort and enhancing the quality of WPSD as well as SSD (Skeletal Subspace Deformation). We show sufficient speed-up of SSD, PSD (Pose Space Deformation) and WPSD to make them suitable for real-time applications.Categories and Subject Descriptors (according to ACM CCS): I.3.1 [Computer Graphics]: Hardware Architecture-Parallel processing, I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling-Curve, surface, solid and object modeling, I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism-Animation.
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    Bayesian Point Cloud Reconstruction
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Jenke, P.; Wand, M.; Bokeloh, M.; Schilling, A.; Strasser, W.
    In this paper, we propose a novel surface reconstruction technique based on Bayesian statistics: The measurement process as well as prior assumptions on the measured objects are modeled as probability distributions and Bayes rule is used to infer a reconstruction of maximum probability. The key idea of this paper is to define both measurements and reconstructions as point clouds and describe all statistical assumptions in terms of this finite dimensional representation. This yields a discretization of the problem that can be solved using numerical optimization techniques. The resulting algorithm reconstructs both topology and geometry in form of a well-sampled point cloud with noise removed. In a final step, this representation is then converted into a triangle mesh. The proposed approach is conceptually simple and easy to extend. We apply the approach to reconstruct piecewise-smooth surfaces with sharp features and examine the performance of the algorithm on different synthetic and real-world data sets.Categories and Subject Descriptors (according to ACM CCS): I.5.1 [Models]: Statistical; I.3.5 [Computer Graphics]: Curve, surface, solid and object representations
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    Topological Structures in Two-Parameter-Dependent 2D Vector Fields
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Weinkauf, T.; Theisel, H.; Hege, H.-C.; Seidel, H.-P.
    In this paper we extract and visualize the topological skeleton of two-parameter-dependent vector fields. This kind of vector data depends on two parameter dimensions, for instance physical time and a scale parameter. We show that two important classes of local bifurcations - fold and Hopf bifurcations - build line structures for which we present an approach to extract them. Furthermore we show that new kinds of structurally stable local bifurcations exist for this data, namely fold-fold and Hopf-fold bifurcations. We present a complete classification of them. We apply our topological extraction method to analyze a number of two-parameter-dependent vector fields with different physical interpretations of the two additional dimensions.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation I.3.3 [Computer Graphics]: Picture/Image Generation
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    Editorial
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Duke, David; Scopigno, Roberto
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    2006 Eurographics Symposium on Parallel Graphics and Visualization
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Paulo Santos, Luis
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    Errata
    (The Eurographics Association and Blackwell Publishing Ltd, 2006)
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    In Memoriam: Professor Dick Grimsdale 1929-2005
    (The Eurographics Association and Blackwell Publishing Ltd., 2006) Willis, Phil
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    Compact Representation of Spectral BRDFs Using Fourier Transform and Spherical Harmonic Expansion
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Xu, Huiying; Sun, Yinlong
    This paper proposes a compact method to represent isotropic spectral BRDFs. In the first step, we perform a Fourier transform in the wavelength dimension. The resulting Fourier coefficients of the same order depend on three angles: the polar angle of the incident light, and the polar and azimuth angles of the outgoing light. In the second step, given an incident light angle, when the Fourier coefficients of the same order have an insensitive dependency on the outgoing direction, we represent these Fourier coefficients using a linear combination of spherical harmonics. Otherwise, we first decompose these Fourier coefficients into a smooth background that corresponds to diffuse component and a sharp lobe that corresponds to specular component. The smooth background is represented using a linear combination of spherical harmonics, and the sharp lobe using a Gaussian function. The representation errors are evaluated using spectral BRDFs obtained from measurement or generated from the Phong model. While maintaining sufficient accuracy, the proposed representation method has achieved data compression over a hundred of times. Examples of spectral rendering using the proposed method are also shown.