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Removing fences from sweep motion videos using global 3D reconstruction and fence-aware light field rendering

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Computational Visual Media 2019年第1期5卷 21-32页

作者： Chanya Lueangwattana Shohei Mori Hideo Saito Department of Science and Technology Keio University institute of computer graphics and Vision Graz University of Technology

Diminishing the appearance of a fence in an image is a challenging research area due to the characteristics of fences(thinness, lack of texture, etc.) and the need for occluded background restoration. In this paper, we describe a fence removal method for an image sequence captured by a user making a sweep motion, in which occluded background is potentially observed. To make use of geometric and appearance information such as consecutive images, we use two well-known approaches: structure from motion and light field rendering. Results using real image sequences show that our method can stably segment fences and preserve background details for various fence and background combinations. A new video without the fence, with frame coherence, can be successfully provided.

关键词： video fence video repair diminished reality(DR) structure from motion(SfM) light field rendering(LFR)

A quadratic programming method for optimal degree reduction of Bézier curves with G^1-continuity

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第10期8卷 1657-1662页

作者： LU Li-zheng WANG Guo-zhao institute of computer graphics and lmage Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

This paper presents a quadratic programming method for optimal multi-degree reduction of B6zier curves with G^1-continuity. The L2 and I2 measures of distances between the two curves are used as the objective functions. The two additional parameters, available from the coincidence of the oriented tangents, are constrained to be positive so as to satisfy the solvability condition. Finally, degree reduction is changed to solve a quadratic problem of two parameters with linear constraints. Applications of degree reduction of Bezier curves with their parameterizations close to arc-length parameterizations are also discussed.

关键词： Degree reduction Bezier curves Optimal approximation G^1-continuity Quadratic programming

CAD-VR geometry and meta data synchronization for design review applications

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第9期7卷 1482-1491页

作者： SCHILLING Arne KIM Seokryul WEISSMANN Daniel TANG Ziying CHOI Sangsu Fraunhofer institute for computer graphics （IGD） Darmstadt 64283 Germany institute for Graphic Interfaces （IGI） Seou1120-750 Korea computer graphics Center （ZGD V） Rostock 18059 Germany

In this paper we present the MEMPHIS middleware framework for the integration of CAD geometries and assemblies with derived Virtual Reality (VR) models and its specific meta data and attributes. The goal of this work is to connect real time VR applications, especially for the Design Review, with enterprise software storing and managing CAD models (Product Data Man- agement—PDM). The preparation of VR models requires expert knowledge, is time consuming, and includes selection of required CAD data, tessellation, healing of unwanted gaps, applying materials and textures, and special surface and light effects. During the Design Review process, decisions are made concerning the choice of materials and surface forms. While materials can be switched directly on the VR model, the modification of part geometries must be made on the CAD model. Our system synchronizes modi- fications of the original CAD geometries and of attributes that are relevant for the realistic rendering using the PLM Services standard. Thus, repeated work for the VR preparation can be avoided.

关键词： Virtual Reality (VR) CAD Product Data Management (PDM) Geometry conversion

Relation among C-curve characterization diagrams

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第10期8卷 1663-1670页

作者： CAO Juan WANG Guo-zhao institute of computer graphics and Image Processing Department of Mathematics Zhejiang University Hangzhou 310027 China

As three control points are fixed and the fourth control point varies, the planar cubic C-curve may take on a loop, a cusp, or zero to two inflection points, depending on the position of the moving point. The plane can, therefore, be partitioned into regions labelled according to the characterization of the curve when the fourth point is in each region. This partitioned plane is called a "characterization diagram". By moving one of the control points but fixing the rest, one can induce different characterization diagrams. In this paper, we investigate the relation among all different characterization diagrams of cubic C-curves based on the singularity conditions proposed by Yang and Wang (2004). We conclude that, no matter what the C-curve type is or which control point varies, the characterization diagrams can be obtained by cutting a common 3D characterization space with a corresponding plane.

关键词： Spline C-curve Characterization diagram Singularity

Constrained multi-degree reduction of rational Bézier curves using reparameterization

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第10期8卷 1650-1656页

作者： CAI Hong-jie WANG Guo-jin institute of computer Images and graphics State Key Laboratory of CAD ＆ CG Zhejiang University Hangzhou 310027 China

Applying homogeneous coordinates, we extend a newly appeared algorithm of best constrained multi-degree reduction for polynomial Bezier curves to the algorithms of constrained multi-degree reduction for rational Bezier curves. The idea is introducing two criteria, variance criterion and ratio criterion, for reparameterization of rational Bezier curves, which are used to make uniform the weights of the rational Bezier curves as accordant as possible, and then do multi-degree reduction for each component in homogeneous coordinates. Compared with the two traditional algorithms of ＂cancelling the best linear common divisor＂ and ＂shifted Chebyshev polynomial＂, the two new algorithms presented here using reparameterization have advantages of simplicity and fast computing, being able to preserve high degrees continuity at the end points of the curves, do multi-degree reduction at one time, and have good approximating effect.

关键词： Rational Bezier curves Constrained multi-degree reduction Reparameterization

Conflict detection and resolution for authorization policies in workflow systems

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第8期10卷 1082-1092页

作者： Chen-hua MA Guo-dong LU Jiong QIU Engineering & computer graphics institute Zhejiang University Hangzhou 310027 China Department of computer Engineering Hangzhou Dianzi University Hangzhou 310008 China

The specification of authorization policies in access control models proposed so far cannot satisfy the requirements in workflow management systems(WFMSs).Furthermore,existing approaches have not provided effective conflict detection and resolution methods to maintain the consistency of authorization polices in *** address these concerns,we propose the definition of authorization policies in which context constraints are considered and the complicated requirements in WFMSs can be *** on the definition,we put forward static and dynamic conflict detection methods for authorization *** defining two new concepts,the precedence establishment rule and the conflict resolution policy,we provide a flexible approach to resolving conflicts.

关键词： Workflow management system (WFMS) Authorization policy Conflict detection and resolution

Control mesh representation of a class of minimal surfaces

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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

Optimal constrained multi-degree reduction of Bézier curves with explicit expressions based on divide and conquer

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第4期10卷 577-582页

作者： Lian ZHOU Guo-jin WANG institute of computer graphics and Image Processing State Key Lab of CAD & CG Zhejiang University Hangzhou 310027 China

We decompose the problem of the optimal multi-degree reduction of Bézier curves with corners constraint into two simpler subproblems, namely making high order interpolations at the two endpoints without degree reduction, and doing optimal degree reduction without making high order interpolations at the two endpoints. Further, we convert the second subproblem into multi-degree reduction of Jacobi polynomials. Then, we can easily derive the optimal solution using orthonormality of Jacobi polynomials and the least square method of unequally accurate measurement. This method of 'divide and conquer' has several advantages including maintaining high continuity at the two endpoints of the curve, doing multi-degree reduction only once, using explicit approximation expressions, estimating error in advance, low time cost, and high precision. More importantly, it is not only deduced simply and directly, but also can be easily extended to the degree reduction of surfaces. Finally, we present two examples to demonstrate the effectiveness of our algorithm.

关键词： Bezier curves Multi-degree reduction Divide and conquer

Optimal approximate merging of a pair of Bézier curves with G^2-continuity

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第4期10卷 554-561页

作者： Ping ZHU Guo-zhao WANG institute of computer graphics and lmage Processing State Key Lab of CAD & CG Zhejiang University Hangzhou 310027 China

We present a novel approach for dealing with optimal approximate merging of two adjacent Bezier eurves with G^2-continuity. Instead of moving the control points, we minimize the distance between the original curves and the merged curve by taking advantage of matrix representation of Bezier curve＇s discrete structure, where the approximation error is measured by L2-norm. We use geometric information about the curves to generate the merged curve, and the approximation error is smaller. We can obtain control points of the merged curve regardless of the degrees of the two original curves. We also discuss the merged curve with point constraints. Numerical examples are provided to demonstrate the effectiveness of our algorithms.

关键词： Approximate merging Gl-continuity G^2-continuity Discrete subdivision Point constraints