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Now showing 1 - 10 of 100
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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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    Silhouette Extraction in Hough Space
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Olson, Matt; Zhang , Hao
    Object-space silhouette extraction is an important problem in fields ranging from non-photorealistic computer graphics to medical robotics. We present an efficient silhouette extractor for triangle meshes under perspective projection and make three contributions. First, we describe a novel application of 3D Hough transforms, which allows us to organize mesh data more effectively for silhouette computations than the traditional dual transform. Next, we introduce an incremental silhouette update algorithm which operates on an octree augmented with neighbour information and optimized for efficient low-level traversal. Finally, we present a method for initial extraction of silhouette, using the same data structure, whose performance is linear in the size of the extracted silhouette. We demonstrate significant performance improvements given by our approach over the current state of the art.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Three-Dimensional Graphics and Realism]: Visible line/surface algorithms
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    Enhancing the Interactive Visualization of Procedurally Encoded Multifield Data with Ellipsoidal Basis Functions
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Jang, Yun; Botchen, Ralf P.; Lauser, Andreas; Ebert, David S.; Gaither, Kelly P.; Ertl, Thomas
    Functional approximation of scattered data is a popular technique for compactly representing various types of datasets in computer graphics, including surface, volume, and vector datasets. Typically, sums of Gaussians or similar radial basis functions are used in the functional approximation and PC graphics hardware is used to quickly evaluate and render these datasets. Previously, researchers presented techniques for spatially-limited spherical Gaussian radial basis function encoding and visualization of volumetric scalar, vector, and multifield datasets. While truncated radially symmetric basis functions are quick to evaluate and simple for encoding optimization, they are not the most appropriate choice for data that is not radially symmetric and are especially problematic for representing linear, planar, and many non-spherical structures. Therefore, we have developed a volumetric approximation and visualization system using ellipsoidal Gaussian functions which provides greater compression, and visually more accurate encodings of volumetric scattered datasets. In this paper, we extend previous work to use ellipsoidal Gaussians as basis functions, create a rendering system to adapt these basis functions to graphics hardware rendering, and evaluate the encoding effectiveness and performance for both spherical Gaussians and ellipsoidal Gaussians.Categories and Subject Descriptors (according to ACMCCS): I.3.3 [Computer Graphics]: Scientific Visualization, Ellipsoidal Basis Functions, Functional Approximation, Texture Advection
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    Memory-Conserving Bounding Volume Hierarchies with Coherent Raytracing
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Mahovsky, J.; Wyvill, B.
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    4th International Workshop on Volume Graphics
    (The Eurographics Association and Blackwell Publishing Ltd., 2006)
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    Virtual Reality Course-A Natural Enrichment of Computer Graphics Classes
    (The Eurographics Association and Blackwell Publishing Ltd., 2006) Zara, J.
    This paper shows how the Virtual Reality (VR) course can naturally extend and practice a wide range of Computer Graphics (CG) principles and programming techniques. Thanks to real-time processing requirements, attention is paid to efficient modeling conventions, time-saving rendering approaches, and user interfaces allowing a smooth navigation in a virtual environment. All these issues play an important role especially when designing virtual worlds targeted to the web, i.e. utilizing VRML/X3D standards. The paper presents a structure and related information of the VR course that has been taught at various universities during the last 6 years. Our experience clearly demonstrates that students appreciate its contents even if they already completed courses on 3D graphics.
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    27th EUROGRAPHICS General Assembly
    (The Eurographics Association and Blackwell Publishing Ltd, 2006)
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    Tuning Subdivision by Minimising Gaussian Curvature Variation Near Extraordinary Vertices
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Augsdoerfer, U.H.; Dodgson, N.A.; Sabin, M.A.
    We present a method for tuning primal stationary subdivision schemes to give the best possible behaviour near extraordinary vertices with respect to curvature variation.Current schemes lead to a limit surface around extraordinary vertices for which the Gaussian curvature diverges, as demonstrated by Karciauskas et al. [KPR04]. Even when coefficients are chosen such that the subsubdominant eigenvalues, , equal the square of the subdominant eigenvalue,, of the subdivision matrix [DS78] there is still variation in the curvature of the subdivision surface around the extraordinary vertex as shown in recent work by Peters and Reif [PR04] illustrated by Karciauskas et al. [KPR04].In our tuning method we optimise within the space of subdivision schemes with bounded curvature to minimise this variation in curvature around the extraordinary vertex. To demonstrate our method we present results for the Catmull-Clark [CC78], 4-8 [Vel01, VZ01] and 4-3 [PS03] subdivision schemes. We compare our results to previous work on the tuning of these schemes and show that the coefficients derived with this method give a significantly smaller curvature variation around extraordinary vertices.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling, I.3.6 [Computer Graphics]: Methodology and Techniques
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    Undersampled Light Field Rendering by a Plane Sweep
    (The Eurographics Association and Blackwell Publishing Ltd, 2006) Liu, Yang; Chen, George; Max, Nelson; Hofsetz, Christian; McGuinness, Peter
    Images synthesized by light field rendering exhibit aliasing artifacts when the light field is undersampled; adding new light field samples improves the image quality and reduces aliasing but new samples are expensive to acquire. Light field rays are traditionally gathered directly from the source images, but new rays can also be inferred through geometry estimation. This paper describes a light field rendering approach based on this principle that estimates geometry from the set of source images using multi-baseline stereo reconstruction to supplement the existing light field rays to meet the minimum sampling requirement. The rendering and reconstruction steps are computed over a set of planes in the scene volume, and output images are synthesized by compositing results from these planes together. The planes are each processed independently and the number of planes can be adjusted to scale the amount of computation to achieve the desired frame rate. The reconstruction fidelity (and by extension image quality) is improved by a library of matching templates to support matches along discontinuities in the image or geometry (e.g. object profiles and concavities). Given a set of silhouette images, the visual hull can be constructed and applied to further improve reconstruction by removing outlier matches. The algorithm is efficiently implemented by a set of image filter operations on commodity graphics hardware and achieves image synthesis at interactive rates.
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    Data Preparation for Real-time High Quality Rendering of Complex Models
    (The Eurographics Association and Blackwell Publishing, Inc, 2006) Klein, Reinhard
    The capability of current 3D acquisition systems to digitize the geometry reflection behaviour of objects as well as the sophisticated application of CAD techniques lead to rapidly growing digital models which pose new challenges for interaction and visualization. Due to the sheer size of the geometry as well as the texture and reflection data which are often in the range of several gigabytes, efficient techniques for analyzing, compressing and rendering are needed. In this talk I will present some of the research we did in our graphics group over the past years motivated by industrial partners in order to automate the data preparation step and allow for real-time high quality rendering e.g. in the context of VR-applications. Strength and limitations of the different techniques will be discussed and future challenges will be identified. The presentation will go along with live demonstrations.