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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

Unequal Forced-Intra-Refresh for robust video streaming

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第10期7卷 1695-1701页

作者： LIU Hao ZHANG Wen-jun YANG Xiao-kang institute of lmage comm.nication and info.mation processing Shanghai Jiao Tong University Shanghai 200240 China

For video streaming over lossy channels, intra refresh can mitigate the error-propagation effect caused by packet losses Besides some intra-mode macroblocks （MBs） generated by the ＂Lagrangian rate-distortion＂ or ＂Sum of absolute difference＂ mode decision, the encoder or transcoder possibly needs to increase some ＂forced＂ intra-mode MBs for robust video streaming. Based on the error-propagation analysis in a group of pictures （GOP）, we propose an unequal Forced-Intra-Refresh （FIR） scheme to improve packet loss resilience of video streaming. According to a GOP-level error-propagation model, the proposed unequal FIR scheme can optimally increase the unequal number of forced intra-mode MBs for different frames in a GOP. Simulation results showed that the proposed scheme can effectively enhance the robustness of video streaming under different channel conditions, and achieve about 0. 1-0.9 dB gains over the average FIR scheme in H.264/AVC tools.

关键词： Video streaming Error propagation Intra refresh Packet loss resilience Group of pictures (GOP)

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 info.mation 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

Mean shift texture surface detection based on WT and COM feature image selection

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第6期7卷 969-975页

作者： HAN Yan-fang SHI Peng-fei institute of lmage processing and Pattern Recognition Shanghai Jiao Tong University Shanghai 200030 China

Mean shift is a widely used clustering algorithm in image segmentation. However, the segmenting results are not so good as expected when dealing with the texture surface due to the influence of the textures. Therefore, an approach based on wavelet transform (WT), co-occurrence matrix (COM) and mean shift is proposed in this paper. First, WT and COM are employed to extract the optimal resolution approximation of the original image as feature image. Then, mean shift is successfully used to obtain better detection results. Finally, experiments are done to show this approach is effective.

关键词： Mean shift Wavelet transform (WT) Co-occurrence matrix (COM) Texture defect detection

Efficient video downscaling transcoder from MPEG-2 to H.264

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第4期9卷 457-463页

作者： Xiang-wen WANG Jun SUN Rong XIE Song-yu YU Shanghai Key Lab. of Digital Media processing ＆ Transmissions Institute of lmage Communication ＆ Information Processing Shanghai Jiao Tong University Shanghai 200240 China

The new H.264 video coding standard achieves significantly higher compression performance than MPEG-2. As the MPEG-2 is popular in digital TV, DVD, etc., bandwidth or memory space can be saved by transcoding those streams into H.264 in these applications. Unfortunately, the huge complexity keeps transcoding from being widely used in practical applications. This paper proposes an efficient transcoding architecture with a smart downscaling decoder and a fast mode decision algorithm. Using the proposed architecture, huge buffering memory space is saved and the transcoding complexity is reduced. Performance of the proposed fast mode decision algorithm is validated by experiments.

关键词： Video transcoding Mode decision Edge direction analysis

Easy cross parameterization for articulated shapes

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第10期10卷 1428-1438页

作者： Jian-wei HU Li-gang LIU Guo-zhao WANG institute of Computer Graphics and lmage processing Department of Mathematics Zhejiang University Hangzhou 310027 China Department of Mathematics Huangshan University Huangshan 245041 China

This paper presents a novel interactive system for establishing compatible meshes for articulated *** two mesh surfaces,our system automatically generates both the global level component correspondence and the local level feature *** can use some sketch-based tools to specify the correspondence in an intuitive and easy *** all the other vertex correspondences could be generated *** cross parameterization preserves both high level and low level features of the *** technique showed in the system benefits various applications in graphics including mesh inter-polation,deformation transfer,and texture transfer.

关键词： Sketch Compatible mesh Vertex correspondence Cross parameterization

Adaptive triangular mesh coarsening with centroidal Voronoi tessellations

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第4期10卷 535-545页

作者： Zhen-yu SHU Guo-zhao WANG Chen-shi DONG institute of Computer Graphics and lmage processing Department of Mathematics Zhejiang University Hangzhou 310027 China Laboratory of info.mation and Optimization Technologies Ningbo Institute of Technology Zhejiang University Ningbo 315100 China

We present a novel algorithm for adaptive triangular mesh coarsening. The algorithm has two stages. First, the input triangular mesh is refined by iteratively applying the adaptive subdivision operator that performs a so-called red-green split. Second, the refined mesh is simplified by a clustering algorithm based on centroidal Voronoi tessellations (CVTs). The accuracy and good quality of the output triangular mesh are achieved by combining adaptive subdivision and the CVTs technique. Test results showed the mesh coarsening scheme to be robust and effective. Examples are shown that validate the method.

关键词： Triangular mesh Mesh coarsening Surface subdivision Centroidal Voronoi tessellations (CVTs)

Iris recognition:a biometric method after refractive surgery

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第8期8卷 1227-1231页

作者： YUAN Xiao-yan ZHOU Hao SHI Peng-fei institute of lmage processing and Pattern Recognition Shanghai Jiao Tong University Shanghai 200240 China Department of Ophthalmology EENT Hospital of Fudan University Shanghai 200031 China

Iris recognition,as a biometric method,outperforms others because of its high accuracy. Iris is the visible internal organ of human,so it is stable and very difficult to be altered. But if an eye surgery must be made to some individuals,it may be rejected by iris recognition system as imposters after the surgery,because the iris pattern was altered or damaged somewhat during surgery and cannot match the iris template stored before the surgery. In this paper,we originally discuss whether refractive surgery for vision correction(LASIK surgery) would influence the performance of iris recognition. And experiments are designed and tested on iris images captured especially for this research from patients before and after refractive surgery. Experiments showed that refractive surgery has little influence on iris recognition.

关键词： Biometric Iris recognition Refractive surgery LASIK Myopia

A smartcard conditional access interface scheme for conditional access subsystem separation in digital TV broadcasting

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第6期7卷 1008-1017页

作者： XIE Qiang ZHENG Shi-bao YU Xiao-jing institute of lmage comm.nication and lnformation processing Shanghai Jiao Tong University Shanghai 200240 China

Conditional access system (CAS) is a key technical component in digital TV broadcasting through which TV op-erators manage the appropriate rights of different subscribers in order to protect their comm.rcial benefits. The normal digital TV receiver can only receive and decode the pay TV programs scrambled by one specific CAS. In this paper, the authors proposed a smartcard conditional access interface (SCAI) scheme in order to make the digital TV receiver be a comm.n receiving platform independent of any specific CAS employed at the broadcasting head-end. As a result, it only needs to include a comm.n condi-tional access software package (CCAP) without any requirement of hardware modification in the receiver. Comparison between the two mentioned DVB-CI-based schemes showed that the cost of such kind receiver is greatly reduced. The main design points of the proposed scheme and its reference implementation’s architecture are presented in this paper. This scheme is also one of the candidate national standards for Chinese digital TV broadcasting industry.

关键词： Digital TV broadcasting Conditional access subsystem separation Smartcard interface