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6th Joint Eurographics - IEEE TCVG Symposium on Visualization, VisSym 2004

作者： Co, Christopher S. Porumbescu, Serban D. Joy, Kenneth I. Center for Image Processing and Integrated Computing Department of Computer Science University of California Davis United States

ISBN: (纸本)390567307X

We propose a meshless method for the extraction of high-quality continuous isosurfaces from volumetric data represented by multiple grids, also called "multiblock"data sets. Multiblock data sets are commonplace in computational mechanics applications. Relatively little research has been performed on contouring multiblock data sets, particularly when the grids overlap one another. Our algorithm proceeds in two steps. In the first step, we determine a continuous interpolant using a set of locally defined radial basis functions (RBFs) in conjunction with a partition of unity method to blend smoothly between these functions. In the second step, we extract isosurface geometry by sampling points on Marching Cubes triangles and projecting these point samples onto the isosurface defined by our interpolant. A surface splatting algorithm is employed for visualizing the resulting point set representing the isosurface. Because of our method's generality, it inherently solves the "crack problem"in isosurface generation. Results using a set of synthetic data sets and a discussion of practical considerations are presented. The importance of our method is that it can be applied to arbitrary grid data regardless of mesh layout or orientation. © The Eurographics Association 2004.

关键词： Computational mechanics

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Medial axis representation and encoding of scanned documents

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Journal of Visual Communication and image Representation 1991年第2期2卷 151-165页

作者： Brandt, Jonathan W. Jain, Anil K. Ralph Algazi, V. Computer Vision Research Lab CIPIC: The Center for Image Processing and Integrated Computing United States Department of Electrical Engineering and Computer Science University of California Davis CA 95616 United States

The medial axis transform (MAT) is a sparse representation of shape, which, being reversible, has potential for binary image compression. The MAT also provides structural information not accessible with alternative binary image codes. This structural information is often used for line extraction and pattern recognition. Therefore, the MAT occupies an interesting middle ground between lower-level, compressible image codes and higher-level, meaningful image representations. In an attempt to realize this middle ground, a MAT-based coding scheme which respects its structural properties is developed. The MAT-based coding method is applied to the CCITT facsimile test images. The resulting compression is comparable to that of known coding schemes for textual and somewhat better for graphical data. Some simple modifications to improve skeleton coding performance are suggested. To substantiate the claim that the MAT is effective for higher-level processing, the representation is extended to perform line segment and curve extraction. The extraction takes place under the control of a global error tolerance parameter and thus provides a new method to trade off data compression with distortion for binary images. © 1991.

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A Study of Transfer Function Generation for Time-Varying Volume Data 2

A Study of Transfer Function Generation for Time-Varying Vol...

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2nd IEEE TCVG / Eurographics International Workshop on Volume Graphics, VG 2001

作者： Jankun-Kelly, T.J. Ma, Kwan-Liu Visualization And Graphics Research Group Center For Image Processing And Integrated Computing University Of California Department Of Computer Science DavisCA95616 United States

ISBN: (纸本)321183737X

The proper usage and creation of transfer functions for time-varying data sets is an often ignored problem in volume visualization. Although methods and guidelines exist for time-invariant data, little formal study for the timevarying case has been performed. This paper examines this problem, and reports the study that we have conducted to determine how the dynamic behavior of time-varying data may be captured by a single or small set of transfer functions. The criteria which dictate when more than one transfer function is needed were also investigated. Four data sets with different temporal characteristics were used for our study. Results obtained using two different classes of methods are discussed, along with lessons learned. These methods, including a new multiresolution opacity map approach, can be used for semi-automatic generation of transfer functions to explore large-scale time-varying data sets. © VG 2001. All rights reserved.

关键词： Transfer functions

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Segmentation-based image compression with enhanced treatment of textured regions 28

Segmentation-based image compression with enhanced treatment...

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28th Asilomar Conference on Signals, Systems and computers, ACSSC 1994

作者： Hussain, Iftekhar Reed, Todd R. Department of Electrical and Computer Engineering Center for Image Processing and Integrated Computing University of California DavisCA95616 United States

ISBN: (纸本)0818664053

This paper presents a method to preprocess an image so that when segmented it yields a partitioning in which textured regions are approximated with a substantially reduced number of uniform regions (which is desirable for the coding). The segmentation method used to form this representation combines a Gaussian texture model and Gibbs-Markov contour model in order to find regions with boundaries which correspond closely to the objects in the image. Given the image segmentation, an approximation to the original image is generated by filling each region with its mean value. If higher quality reconstruction is desired, the quantized approximation error is also encoded. In order to exploit the reduced sensitivity of the human visual system to the error around edges (visual masking), the error is quantized using three nonlinear quantizers corresponding to the smoothly varying, textured, and remaining areas of the image, respectively. © 1995 IEEE.

关键词： Errors

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Improving topological segmentation of three-dimensional vector fields

Improving topological segmentation of three-dimensional vect...

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5th Joint Eurographics - IEEE TCVG Symposium on Visualization, VisSym 2003

作者： Mahrous, Karim M. Bennett, Janine C. Hamann, Bernd Joy, Kenneth I. Center for Image Processing and Integrated Computing Department of Computer Science University of California Davis DavisCA95616-8562 United States

ISBN: (纸本)3905673010

We present three enhancements to accelerate the extraction of separatrices of three-dimensional vector fields, using intelligently selected .sample. streamlines. These enhancements reduce the number of needed sample streamlines and their propagation length. Inflow/outflow matching supports the simultaneous extraction of topologically significant inflow and outflow separatrices in a single pass. An adaptive sampling approach is introduced and used to seed streamlines in a more meaningful and efficient manner. Cell-locking is a new concept that isolates regions of a data set that do not contain separatrices. This concept makes streamline propagation more efficient as streamlines are not propagated through cells that do not influence or contain separatrices. These enhancements enable us to perform separatrix construction for three-dimensional vector field data requiring less overall computation. © 2003 Eurographics Association. All rights reserved.

关键词： Extraction

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Optimal linear spline approximation of digitized models

Optimal linear spline approximation of digitized models

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IEEE International Conference on Information Visualization, IV 1999

作者： Hamann, Bemd Kreylos, Oliver Monno, Giuseppe Uva, Antonio E. Center for Image Processing and Integrated Computing Department of Computer Science University of California DavisCA United States Dipartimento di Progettazione e Produzione Industriale Politecnico di Bari Bari Italy

ISBN: (纸本)0769502105

In this paper we present a new technique for surface reconstruction of digitized models in three dimensions. Concerning this problem, we are given a data set in threedimensional space, represented as a set of points without connectivity information, and the goal is to find, for a Jxed number of vertices, a set of approximating triangles which minimize the error measured by the displacement from the given points. Our method creates near-optimal linear spline approximations, using an iterative optimization scheme based on simulated annealing. The algorithm adapts the mesh to the data set and moves the triangles to enhance feature lines. .4 t the end, we can use the approach to create a hierarchy of dtfferent resolutions for the model. © 1999 IEEE.

关键词： Simulated annealing

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Two applications of wavelets and related techniques in medical imaging

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Annals of Biomedical Engineering 1995年第5期23卷 637-665页

作者： Healy Jr., Dennis M. Lu, Jian Weaver, John B. Department of Mathematics and Computer Science Dartmouth College Hanover 03755 NH United States Center for Image Processing and Integrated Computing University of California Davis CA United States Department of Diagnostic Radiology Dartmouth-Hitchcock Medical Center Lebanon NH United States

We present two applications of wavelet and related techniques to problems arising in medical imaging. Both make considerable use of the edge detection and classification properties of wavelet-type representations. First we describe simple and effective techniques for image denoising and contrast enhancement based on the multiscale edge representation of images. These techniques are sufficiently flexible to successfully address the varying requirements posed by several different medical imaging modalities in common use today. Experimental results are presented to illustrate the application of these techniques to various types of medical images. Next we describe adapted waveform encoding, a technique for magnetic resonance imaging. One advantage of this technique istthat it can be used to efficiently encode edge features of the object being imaged. This has a particular diagnostic application in tracking heart wall thickness during the cardiac cycle, which we present along with some experimental results along this line. We also present an analysis of the signal-to-noise ratios of images formed with this technique, as this is a factor of paramount importance in MRI. The fact that wavelet schemes tend to concentrate energy near edge features makes the result rather different than that found in standard Fourier based approaches. We indicate an exciting potential application of our technique: reducing spectral leakage in phosphorus spectroscopy. © 1995 Biomedical Engineering Society.

关键词： image enhancement Magnetic resonance imaging

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Smooth hierarchical surface triangulations 97

Smooth hierarchical surface triangulations

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Proceedings of the 8th conference on Visualization '97

作者： Tran S. Gieng Bernd Hamann Kenneth I. Joy Gregory L. Schussman Issac J. Trotts Center for Image Processing and Integrated Computing Department of Computer Science University of California Davis

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Simplification of tetrahedral meshes

Simplification of tetrahedral meshes

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IEEE Conference on Visualization

作者： I.J. Trotts B. Hamann K.I. Joy D.F. Wiley Center for Image Processing and Integrated Computing Department of Computer Science University of California Davis USA

We present a method for the construction of multiple levels of tetrahedral meshes approximating a trivariate function at different levels of detail. Starting with an initial, high-resolution triangulation of a three-dimensional region, we construct coarser representation levels by collapsing tetrahedra. Each triangulation defines a linear spline function, where the function values associated with the vertices are the spline coefficients. Based on predicted errors, we collapse tetrahedron in the grid that do not cause the maximum error to exceed a use-specified threshold. Bounds are stored for individual tetrahedra and are updated as the mesh is simplified. We continue the simplification process until a certain error is reached. The result is a hierarchical data description suited for the efficient visualization of large data sets at varying levels of detail.

关键词： Data visualization Spline Legged locomotion Mesh generation image processing computer science Acoustic scattering Large-scale systems Temperature dependence Chemicals

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Using isosurface methods for visualizing the envelope of a swept trivariate solid

Using isosurface methods for visualizing the envelope of a s...

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Pacific Conference on computer Graphics and Applications

作者： J. Conkey K.I. Joy Center for Image Processing and Integrated Computing Department of Computer Science University of California Davis USA

We present a method for calculating the envelope surface of a parametric solid object swept along a path in three-dimensional space. The boundary surface of the solid is the combination of parametric surfaces and an implicit surface where the Jacobian of the defining function has a rank deficiency condition. Using this condition, we determine a set of square sub-Jacobian determinants that must all vanish simultaneously on the implicit surface. When the generator of the swept surface is a trivariate tensor-product B-spline solid and the path is a B-spline curve, we can give a robust algorithm to determine the implicit surface. This algorithm is based upon the "marching tetrahedra" method, which is adapted to work on 4-simplices. The envelope of the swept solid is given by the union of the parametric and implicit surfaces.

关键词： Isosurfaces Visualization Spline Jacobian matrices Robustness image processing computer science Testing Solid modeling

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