25-Issue 4
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Item Compact Representation of Spectral BRDFs Using Fourier Transform and Spherical Harmonic Expansion(The Eurographics Association and Blackwell Publishing Ltd, 2006) Xu, Huiying; Sun, YinlongThis 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.Item 2006 Eurographics Symposium on Parallel Graphics and Visualization(The Eurographics Association and Blackwell Publishing Ltd, 2006) Paulo Santos, LuisItem AFRIGRAPH: Computer Graphics in Africa(The Eurographics Association and Blackwell Publishing Ltd, 2006) Gain, J. E.; Strasser, W.Item Compression of Dense and Regular Point Clouds(The Eurographics Association and Blackwell Publishing Ltd, 2006) Merry, Bruce; Marais, Patrick; Gain, JamesWe present a simple technique for single-rate compression of point clouds sampled from a surface, based on a spanning tree of the points. Unlike previous methods, we predict future vertices using both a linear predictor, which uses the previous edge as a predictor for the current edge, and lateral predictors that rotate the previous edge 90 left or right about an estimated normal.By careful construction of the spanning tree and choice of prediction rules, our method improves upon existing compression rates when applied to regularly sampled point sets, such as those produced by laser range scanning or uniform tesselation of higher-order surfaces. For less regular sets of points, the compression rate is still generally within 1.5 bits per point of other compression algorithms.Item Translational Covering of Closed Planar Cubic B-Spline Curves(The Eurographics Association and Blackwell Publishing Ltd, 2006) Neacsu, Cristina; Daniels, KarenSpline curves are useful in a variety of geometric modeling and graphics applications and covering problems abound in practical settings. This work defines a class of covering decision problems for shapes bounded by spline curves. As a first step in addressing these problems, this paper treats translational spline covering for planar, uniform, cubic B-splines. Inner and outer polygonal approximations to the spline regions are generated using enclosures that are inside two different types of piecewise-linear envelopes. Our recent polygonal covering technique is then applied to seek translations of the covering shapes that allow them to fully cover the target shape. A feasible solution to the polygonal instance provides a feasible solution to the spline instance. We use our recent proof that 2D translational polygonal covering is NP-hard to establish NP-hardness of our planar translational spline covering problem. Our polygonal approximation strategy creates approximations that are tight, yet the number of vertices is only a linear function of the number of control points. Using recent results on B-spline curve envelopes, we bound the distance from the spline curve to its approximation. We balance the two competing objectives of tightness vs. number of points in the approximation, which is crucial given the NP-hardness of the spline problem. Examples of the results of our spline covering work are provided for instances containing as many as six covering shapes, including both convex and nonconvex regions. Our implementation uses the LEDA and CGAL C++ libraries of geometric data structures and algorithms.Item A Randomized Approach for Patch-based Texture Synthesis using Wavelets(The Eurographics Association and Blackwell Publishing Ltd, 2006) Tonietto, L.; Walter, M.; Jung, C. R.We present a wavelet-based approach for selecting patches in patch-based texture synthesis. We randomly select the first block that satisfies a minimum error criterion, computed from the wavelet coefficients (using 1D or 2D wavelets) for the overlapping region. We show that our wavelet-based approach improves texture synthesis for samples where previous work fails, mainly textures with prominent aligned features. Also, it generates similar quality textures when compared against texture synthesis using feature maps with the advantage that our proposed method uses implicit edge information (since it is embedded in the wavelet coefficients) whereas feature maps rely explicitly on edge features. In previous work, the best patches are selected among all possible using a L2 norm on the RGB or grayscale pixel values of boundary zones. The L2 metric provides the raw pixel-to-pixel difference, disregarding relevant image structures - such as edges - that are relevant in the human visual system and therefore on synthesis of new textures.Item Pose Controlled Physically Based Motion(The Eurographics Association and Blackwell Publishing Ltd, 2006) Fattal, Raanan; Lischinski, DaniIn this paper we describe a new method for generating and controlling physically-based motion of complex articulated characters. Our goal is to create motion from scratch, where the animator provides a small amount of input and gets in return a highly detailed and physically plausible motion. Our method relieves the animator from the burden of enforcing physical plausibility, but at the same time provides full control over the internal DOFs of the articulated character via a familiar interface. Control over the global DOFs is also provided by supporting kinematic constraints. Unconstrained portions of the motion are generated in real time, since the character is driven by joint torques generated by simple feedback controllers. Although kinematic constraints are satisfied using an iterative search (shooting), this process is typically inexpensive, since it only adjusts a few DOFs at a few time instances. The low expense of the optimization, combined with the ability to generate unconstrained motions in real time yields an efficient and practical tool, which is particularly attractive for high inertia motions with a relatively small number of kinematic constraints.Item Author Index Volume 25 (2006)(The Eurographics Association and Blackwell Publishing Ltd, 2006)Item REPORT OF THE STATUTORY AUDITORS TO THE GENERAL MEETING OF THE MEMBERS OF EUROGRAPHICS ASSOCIATION GENEVA(The Eurographics Association and Blackwell Publishing Ltd, 2006)Item Occlusion-Driven Scene Sorting for Efficient Culling(The Eurographics Association and Blackwell Publishing Ltd, 2006) Staneker, Dirk; Bartz, Dirk; Wolfgang, StrasserImage space occlusion culling is a powerful approach to reduce the rendering load of large polygonal models. However, occlusion culling is not for free; it trades overhead costs with the rendering costs of the possibly occluded geometry. Meanwhile, occlusion queries based on image space occlusion culling are supported on modern graphics hardware. However, a significant consumption of fillrate bandwidth and latency costs are associated with these queries.In this paper, we propose new techniques to reduce redundant occlusion queries. Our approach uses several "Occupancy Maps" to organize scene traversal. The respective information is accumulated efficiently by hardware-supported asynchronous occlusion queries. To avoid redundant requests, we arrange these multiple occlusion queries according to the information of the Occupancy Maps. Our presented technique is conservative and benefits from a partial depth order of the geometry.Item Soft Shadow Maps: Efficient Sampling of Light Source Visibility(The Eurographics Association and Blackwell Publishing Ltd, 2006) Atty, Lionel; Holzschuch, Nicolas; Lapierre, Marc; Hasenfratz, Jean-Marc; Hansen, Charles; Sillion, Francois X.Shadows, particularly soft shadows, play an important role in the visual perception of a scene by providing visual cues about the shape and position of objects. Several recent algorithms produce soft shadows at interactive rates, but they do not scale well with the number of polygons in the scene or only compute the outer penumbra. In this paper, we present a new algorithm for computing interactive soft shadows on the GPU. Our new approach provides both inner- and outer-penumbra for a modest computational cost, providing interactive frame-rates for models with hundreds of thousands of polygons.Our technique is based on a sampled image of the occluders, as in shadow map techniques. These shadow samples are used in a novel manner, computing their effect on a second projective shadow texture using fragment programs. In essence, the fraction of the light source area hidden by each sample is accumulated at each texel position of this Soft Shadow Map. We include an extensive study of the approximations caused by our algorithm, as well as its computational costs.Item Anisotropic Point Set Surfaces(The Eurographics Association and Blackwell Publishing Ltd, 2006) Adamson, A.; Alexa, M.Point Set Surfaces define smooth surfaces from regular samples based on weighted averaging of the points. Because weighting is done based on a spatial scale parameter, point set surfaces apply basically only to regular samples. We suggest to attach individual weight functions to each sample rather than to the location in space. This extends Point Set Surfaces to irregular settings, including anisotropic sampling adjusting to the principal curvatures of the surface. In particular, we describe how to represent surfaces with ellipsoidal weight functions per sample. Details of deriving such a representation from typical inputs and computing points on the surface are discussed.Item The John Lansdown Award 2006(The Eurographics Association and Blackwell Publishing Ltd, 2006) Duce, DavidItem Differential Representations for Mesh Processing(The Eurographics Association and Blackwell Publishing Ltd, 2006) Sorkine, OlgaSurface representation and processing is one of the key topics in computer graphics and geometric modeling, since it greatly affects the range of possible applications. In this paper we will present recent advances in geometry processing that are related to the Laplacian processing framework and differential representations. This framework is based on linear operators defined on polygonal meshes, and furnishes a variety of processing applications, such as shape approximation and compact representation, mesh editing, watermarking and morphing. The core of the framework is the definition of differential coordinates and new bases for efficient mesh geometry representation, based on the mesh Laplacian operator.Item GRAPP 2006 International Conference on Computer Graphics Theory and Applications(The Eurographics Association and Blackwell Publishing Ltd, 2006) Barhak, JacobItem GEncode: Geometry-driven compression for General Meshes(The Eurographics Association and Blackwell Publishing Ltd, 2006) Lewiner, Thomas; Craizer, Marcos; Lopes, Helio; Pesco, Sinesio; Velho, Luiz; Medeiros, EsdrasPerformances of actual mesh compression algorithms vary significantly depending on the type of model it encodes. These methods rely on prior assumptions on the mesh to be efficient, such as regular connectivity, simple topology and similarity between its elements. However, these priors are implicit in usual schemes, harming their suitability for specific models. In particular, connectivity-driven schemes are difficult to generalize to higher dimensions and to handle topological singularities. GEncode is a new single-rate, geometry-driven compression scheme where prior knowledge of the mesh is plugged into the coder in an explicit manner. It encodes meshes of arbitrary dimension without topological restrictions, but can incorporate topological properties, such as manifoldness, to improve the compression ratio. Prior knowledge of the geometry is taken as an input of the algorithm, represented by a function of the local geometry. This suits particularly well for scanned and remeshed models, where exact geometric priors are available. Compression results surfaces and volumes are competitive with existing schemes.Item 27th EUROGRAPHICS General Assembly(The Eurographics Association and Blackwell Publishing Ltd, 2006)Item 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, FormicoItem Symposium on Geometry Processing 2006: Cagliari, Italy, June 26-28 2006(The Eurographics Association and Blackwell Publishing Ltd, 2006) Sheffer, Alla; Polthier, KonradItem New EUROGRAPHICS Fellows(The Eurographics Association and Blackwell Publishing Ltd, 2006)