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Control mesh representation of a class of minimal surfaces

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第9期7卷 1544-1549页

作者： XU Gang WANG Guo-zhao Institute of Computer Graphics and Image Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

Minimal surface is extensively employed in many areas. In this paper, we propose a control mesh representation of a class of minimal surfaces, called generalized helicoid minimal surfaces, which contain the right helicoid and catenoid as special examples. We firstly construct the Bézier-like basis called AHT Bézier basis in the space spanned by {1, t, sint, cost, sinht, cosht}, t∈[0,α], α∈[0,5π/2]. Then we propose the control mesh representation of the generalized helicoid using the AHT Bézier basis. This kind of representation enables generating the minimal surfaces using the de Casteljau-like algorithm in CAD/CAGD mod- elling systems.

关键词： Minimal surface Helicoid surface Catenoid Control mesh

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Symmetric alteration of four knots of B-spline and NURBS surfaces

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第6期7卷 1084-1087页

作者： LI Ya-juan WANG Guo-zhao Institute of Computer Graphics and Image Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

Modifying the knots of a B-spline curve, the shape of the curve will be changed. In this paper, we present the effect of the symmetric alteration of four knots of the B-spline and the NURBS surfaces, i.e., symmetrical alteration of the knots of surface, the extended paths of points of the surface will converge to a point which should be expressed with several control points. This theory can be used in the constrained shape modification of B-spline and NURBS surfaces.

关键词： B-spline surface NURBS surface Knot modification Path

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Conversion matrix between two bases of the algebraic hyperbolic space

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Journal of Zhejiang University: Science 2006年第SUPPL. 2期7卷 181-186页

作者： Fan, Feng-Tao Wang, Guo-Zhao Institute of Computer Graphics and Image Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

This paper presents the matrix representation for the hyperbolic polynomial B-spline basis and the algebraic hyperbolic Bézier basis in a recursive way, which are both generated over the space Ωn=span{sinht, cosht, tn-3, , t, 1} in which n is an arbitrary integer larger than or equal to 3. The conversion matrix from the hyperbolic polynomial B-spline basis of arbitrary order to the algebraic hyperbolic Bézier basis of the same order is also given by a recursive approach. As examples, the specific expressions of the matrix representation for the hyperbolic polynomial B-spline basis of order 4 and the algebraic hyperbolic Bézier basis of order 4 are given, and we also construct the conversion matrix between the two bases of order 4 by the method proposed in the paper. The results in this paper are useful for the evaluation and conversion of the curves and surfaces constructed by the two bases.

关键词： computer graphics

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Optimal multi-degree reduction of Bézier curves with G1-continuity

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Journal of Zhejiang University: Science 2006年第SUPPL. 2期7卷 174-180页

作者： Lu, Li-Zheng Wang, Guo-Zhao Institute of Computer Graphics and Image Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

This paper presents a novel approach to consider optimal multi-degree reduction of Bézier curve with G1-continuity. By minimizing the distances between corresponding control points of the two curves through degree raising, optimal approximation is achieved. In contrast to traditional methods, which typically consider the components of the curve separately, we use geometric information on the curve to generate the degree reduction. So positions and tangents are preserved at the two endpoints. For satisfying the solvability condition, we propose another improved algorithm based on regularization terms. Finally, numerical examples demonstrate the effectiveness of our algorithms.

关键词： computer graphics

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Twin and scratch detection and removal in micrograph images of inconel™718

Twin and scratch detection and removal in micrograph images ...

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Machine Vision Applications in Industrial Inspection XIV

作者： Jakob, Gerhard Rinnhofer, Alfred Bischof, Horst Benesova, Wanda Joanneum Research Institute of Digital Image Processing Wastiangasse 6 8045 Graz Austria Technical University Graz Institute for Computer Graphics and Vision Inffeldgasse 16/II 8010 Graz Austria

ISBN: (纸本)0819461105

Grain size of forged nickel alloy is an important feature for the mechanical properties of the material. For fully automatic grain size evaluation in images of micrographs it is necessary to detect the boundaries of each grain. This grain boundary detection is influenced directly by artifacts like scratches and twins. Twins can be seen as parallel lines inside one grain, whereas a scratch can be identified as a sequence of collinear line segments that can be spread over the whole image. Both kinds of artifacts introduce artificial boundaries inside grains. To avoid wrong grain size evaluation, it is necessary to remove these artifacts prior to the size evaluation process. For the generation of boundary images various algorithms have been tested. The most stable results were achieved by grayscale reconstruction and a subsequent watershed segmentation. A modified line Hough transform with a third dimension in the Hough accumulator space, describing the distance of the parallel lines, is used to directly detect twins. Scratch detection is done by applying the standard line Hough transform followed by a rule based segment detection along the found Hough lines. The results of these operations give a detection rate of more than 90 percent for twins and more than 50 percent for scratches. © 2006 SPIE-IS&T.

关键词： Object recognition

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Harmonic-type Bézier surface over rectangular and triangular domain

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Journal of Information and Computational Science 2006年第2期3卷 325-332页

作者： Xu, Gang Wang, Guozhao Institute of Computer Graphics and Image Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

In this paper, we present the modeling schemes of a class of Bézier surface with negative Gaussian curvature over the rectangular domain and the triangular domain. We have proved that the surface over the rectangular domain is fully determined by the control points of the two opposed boundary curves, and the surface over the triangular domain is fully determined by the control points on the first and second layers. In particular, we can control the shape of the surface by the shape parameter, which increases the degree of freedom of surface modeling.

关键词： computer graphics

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3D and Infrared Face Reconstruction from RGB data using Canonical Correlation Analysis

3D and Infrared Face Reconstruction from RGB data using Cano...

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International Conference on Pattern Recognition

作者： M. Reiter R. Donner G. Langs H. Bischof Pattern Recognition and Image Processing Group Vienna University of Technology Austria Graz University of Technology Institute for Computer Graphics and Vision Austria

In this paper, we apply a multiple regression method based on canonical correlation analysis (CCA) to face data modelling. CCA is a factor analysis method which exploits the correlation between two high dimensional signals. We first use CCA to perform 3D face reconstruction and in a separate application we predict near-infrared (NIR) face texture. In both cases, the input data are color (RGB) face images. Experiments show, that due to the correlation between input and output signal, only a small number of canonical factors are needed to describe the functional relation of RGB images to the respective output (NIR images and 3D depth maps) with reasonable accuracy

关键词： Shape Face detection Lighting image reconstruction image analysis image databases Pattern analysis Rendering (computer graphics) image color analysis Pattern recognition

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Multi-step integer algorithm for non-unit voxel traversing along a 3D line

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Jisuanji Fuzhu Sheji Yu Tuxingxue Xuebao/Journal of computer-Aided Design and computer graphics 2006年第6期18卷 812-818页

作者： Liu, Yongkui Yun, Jian Wang, Xiaoqiang Song, Haiyu Institute of Computer Graphics and Image Processing Dalian Nationalities University Dalian 116600 China

An algorithm for traversing voxels along a 3D line using only integer arithmetic is presented. Two kinds of subdivision, namely non-unit space subdivision and non-square space subdivision, could be used. A 2D algorithm is first developed to find out the pixels a line passes through. Then based on it, an algorithm for traversing voxels along a 3D line in uniformly divided voxel space is proposed. Up to 3 voxels may be processed in one step and no accumulated error is made. The discriminator used in this algorithm is well refined, so that few calculations are required and the algorithm is simple and compact in form. Its comparison with existing voxel traversal algorithms shows that the new algorithm is not only free from accumulated error but also is the fastest.

关键词： 3D line generation Algorithm Traversal Voxel

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Active Feature Models

Active Feature Models

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International Conference on Pattern Recognition

作者： G. Langs P. Peloschek R. Donner M. Reiter H. Bischof Institute for Computer Graphics and Vision Graz University of Technology Austria Pattern Recognition and Image Processing Group University of Technology Vienna Austria Department of Radiology Medical University of Vienna Austria

ISBN: (纸本)0769525210

In this paper active feature models are proposed. They utilize local texture features and a statistical shape model for the reliable localization of landmarks in images. They are related to active appearance models, but instead of modelling the entire texture of an object they represent image texture by means of local descriptors. The approach has advantages with complex image data like anatomical structures that exhibit high texture variation with limited relevance for the recognition of the object location. Experimental results and the comparison to AAMs on different data sets indicate that active feature models can improve search speed and result accuracy, considerably

关键词： Shape Active appearance model Biomedical imaging image texture image edge detection image texture analysis computer graphics Pattern recognition image processing Radiology

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Automatic Surveying of Cutaneous Hemangiomas

Automatic Surveying of Cutaneous Hemangiomas

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International Conference on Pattern Recognition

作者： S. Zambanini G. Langs R. Sablatnig P. Donath H. Maier Pattern Recognition and Image Processing Group University of Technology Vienna Austria Institute for Computer Graphics and Vision Graz University of Technology Austria Division of Special and Environmental Dermatologyy Medical University of Vienna Austria

This paper presents a method for the fully automatic surveying of cutaneous hemangiomas by means of a hemangioma segmentation and a ruler visible in the images. The algorithm computes the spatial resolution of an image. Hemangioma segmentation is accomplished by a single-layer perceptron classification by means of pixel color features. The algorithm was evaluated on a set of 120 images. It achieves satisfactory results on images with clearly visible, saturated hemangiomas

关键词： image segmentation Neoplasms Pattern recognition Spatial resolution Lesions Area measurement Pixel image processing computer graphics Biomedical imaging

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