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Now showing 1 - 10 of 23
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    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.
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    27th EUROGRAPHICS General Assembly
    (The Eurographics Association and Blackwell Publishing Ltd, 2006)
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    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, Esdras
    Performances 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.
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    Differential Representations for Mesh Processing
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Sorkine, Olga
    Surface 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.
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    Occlusion-Driven Scene Sorting for Efficient Culling
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Staneker, Dirk; Bartz, Dirk; Wolfgang, Strasser
    Image 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.
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    Compression of Dense and Regular Point Clouds
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Merry, Bruce; Marais, Patrick; Gain, James
    We 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.
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    Translational Covering of Closed Planar Cubic B-Spline Curves
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Neacsu, Cristina; Daniels, Karen
    Spline 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.
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    Author Index Volume 25 (2006)
    (The Eurographics Association and Blackwell Publishing Ltd, 2006)
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    GRAPP 2006 International Conference on Computer Graphics Theory and Applications
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Barhak, Jacob