A new corner detection algorithm for chain code representation

A new algorithm is proposed to detect a corner of a thinned binary image that is represented by an eight-connected contour chain code. The algorithm is based on chain-coded image, deriving the slope between each code, analyze the series of chain code, and finally decide the existence of corner at the current pixel location. The work assumes that the pre-processing processes on the image, namely thinning and digitization, have been done. Two weighted parameters identified as significant factors in determining the accuracy of the corner detection algorithm are discussed. The parameters are the length of segment and threshold value. Computational phases to derive values of rows and columns given a series of chain code are also given in detail. The algorithm can be used to interpret line drawing that represents three-dimensional object.     

鲁棒的二值图像并行细化算法

通过分析两种典型的并行细化算法,提出一种新的增强并行细化算法（Enhanced Parallel Thinning Algorithm,EPTA）．经过大量对比实验表明,新算法能很好解决斜线信息丢失、冗余像素和多余枝杈问题,且效率高、鲁棒性强．     

一种最优化链码指纹二值细化图像压缩编码

提出了一种适合于对线状结构的条形纹线二值图像进行压缩的最优化Freeman链码压缩算法——Freeman差分链码Huffman编码。与传统的Freeman链码相比,提出的压缩算法是基于Freeman链码、差分编码和Huffman编码的一种混和编码方式。通过理论分析和在指纹二值细化图上的实验结果证明,对于指纹二值细化图像,本算法优于现有的链码压缩二值图像的算法,针对于线状结构的条形纹线二值图像,本算法也优于其他压缩算法。其平均码长为1.7651bits,低于8方向Freeman链码或者Freeman差分链码的3bits的平均码长。     

A contour tracing and coding algorithm for generating 2D contour codes from 3D classified objects

In 3D image data sets generated by voxel-based classification, each voxel is marked with a specific class label. Voxels of the same class label can form 3D objects of extremely complex shape. Interactively drawn regions are usually represented by their 2D region borders. In order to combine automatically classified with interactively drawn regions, a contour tracing and coding algorithm for generating optimized 2D contours from 3D classified objects is presented. A special conversion algorithm allows a chain or a crack code representation. An application to medical images shows the method's necessity and usefulness in dealing with highly complex regions.     

Efficiency of chain codes to represent binary objects

We present a study of compression efficiency for binary objects or bi-level images for different chain-code schemes. Chain-code techniques are used for compression of bi-level images because they preserve information and allow a considerable data reduction. Furthermore, chain codes are the standard input format for numerous shape-analysis algorithms. In this work we apply chain codes to represent object with holes and we compare their compression efficiency for seven chain codes. We have also compared all these chain codes with the JBIG standard for bi-level images.     

Finding a minimal cover for binary images: An optimal parallel algorithm

Given a black-and-white image, represented by an array of n × n binary-valued pixels, we wish to cover the black pixels with aminimal set of (possibly overlapping) maximal squares. It was recently shown that obtaining aminimum square cover for a polygonal binary image with holes is NP-hard. We derive an optimal parallel algorithm for theminimal square cover problem, which for any desired computation timeT in [logn,n] runs on an EREW-PRAM with (n/T) processors. The cornerstone of our algorithm is a novel data structure, the cover graph, which compactly represents the covering relationships between the maximal squares of the image. The size of the cover graph is linear in the number of pixels. This algorithm has applications to problems in VLSI mask generation, incremental update of raster displays, and image compression.The research reported here forms part of the author's doctoral dissertion, submitted to Cornell University in May 1989. This work was partially supported by NSF Grant DC1-86-02256, IBM Agreement 12060043, and ONR Contract N00014-83-K-0640. A preliminary version of this paper was presented at the 26th Annual Allerton Conference on Communications, Control, and Computing, Monticello, IL, September 28–30, 1988.     

An efficient chain code with Huffman coding

This paper presents a new chain code based on the eight-direction Freeman code. Each element in the chain is coded as a relative angle difference between it and the previous element. Statistical analysis showed that the probabilities of the Freeman codes differ importantly. Therefore, the Huffman coding was applied. The proposed chain code requires 1.97 bits/code, its chain length is short, it allows the representation of non-closed patterns, and it is rotationally independent.     

基于链码技术的距离变换改进算法

论述了分水岭算法的原理及距离变换的具体过程。为了提高距离转换算法速度,提出了利用链码技术改进距离变换的算法。该方法利用链码技术能够准确跟踪目标物体边界的特点,按不同层次轮廓点灰度级递增的方式逐层对目标物体进行遍历,完成图像的距离转换,克服了形态学距离变换算法多次腐蚀、扫描图像,时间消耗较大的缺点。经过在木材细胞图像的分割过程中,同现有的距离变换算法比较证明,改进方法提高了距离变换速度,对提高图像分割的效率具有重要意义。     

A parallel median algorithm

We give a deterministic algorithm for finding the kth smallest item in a set of n items, running in O((log log n)²) parallel time on O(n) processors in Valiant's comparison model.     

Fast template matching algorithm for contour images based on its chain coded description applied for human face identification

A new matching algorithm for contour images described by chain coded expression is presented. In our face authentication system, the isodensity contours has been introduced to differentiate between the facial features. These isodensity contours can be transformed into chain codes. By using these coded isodensity contours, remarkable improvement in the processing performance can be expected in terms of the processing time and memory requirements.From the computer simulation performed using images of 50 people, it turned out clear that the processing time was decreased to approximately one-seventh compared to the conventional method. With respect to memory requirement, it was reduced to a quarter.     

A parallel decoding algorithm for LZ2 data compression

The LZ2 compression method is hardly parallelizable since it is known to be P-complete. In spite of such negative result, we show in this paper that the decoding process can be parallelized efficiently on an EREW PRAM model of computation with O(n/log(n)) processors and O(log² n) time, where n is the length of the output string.     

A parallel algorithm for generating bicompatible elimination orderings of proper interval graphs

In this paper, we first show how a certain ordering of vertices, called bicompatible elimination ordering (BCO), of a proper interval graph can be used to solve efficiently several problems in proper interval graphs. We, then, propose an NC parallel algorithm (i.e., polylogarithmic-time employing a polynomial number of processors) in SIMD CRCW PRAM (Single Instruction Stream Multiple Data Stream Concurrent Read Concurrent Write Parallel Random Access Machine) model of parallel computation to compute a BCO of a proper interval graph. To the best of our knowledge, this is the first NC parallel algorithm to compute a BCO of a proper interval graph.     

Two undecidability results for chain code picture languages

It is undecidable whether or not two 1-retreat-bounded regular languages describe exactly the same set of pictures or they describe a picture in common.     

二进制文件结构化比较的并行算法实现

为了提高二进制文件结构化比较的效率，提出了一种基于全局地址空间编程模型实现的并行结构化比较算法，将整个结构化比较过程分为并发获取比对信息和并行结构化比较两个子模块。该算法充分利用UPC语言的亲缘性特征，将共享访问私有化，减少通信开销。并通过有效的负载平衡方法，在机群系统上实现了该并行程序。实际数据的测试结果表明，此并行算法是高效的而且可扩展性较好。     

A nearly optimal deterministic parallel Voronoi diagram algorithm

We describe ann-processor,O(log(n) log log(n))-time CRCW algorithm to construct the Voronoi diagram for a set ofn point-sites in the plane.A preliminary version of this paper was presented at the 17th EATCS ICALP meeting at Warwick, England, in July 1990.Supported by the US NSF under Grants CCR 890221 and CCR 8906949.Supported by the US NSF under Grants CCR 8810568, CCR-9003299, and IRI-9116843, and by the NSF and DARPA under Grant CCR 8908092.Supported by the EU Esprit program under BRAs 3075 (ALCOM) and 7141 (ALCOM II).     

Pyramidal thinning algorithm for SIMD parallel machines

We propose a parallel thinning algorithm for binary pictures. Given an N × N binary image including an object, our algorithm computes in O(N²) the skeleton of the object, using a pyramidal decomposition of the picture. The behavior of this algorithm is studied considering a family of digitalization of the same object at a different level of resolution. With the Exclusive Read Exclusive Write (EREW) Parallel Random Access Machine (PRAM), our algorithm runs in O(log N) time using O(N²/logN) processors and it is work-optimal. The same result is obtained with high-connectivity distributed memory SIMD machines having strong hypercube and pyramid. We describe the basic operator, the pyramidal algorithm and some experimental results on the SIMD MasPar parallel machine.     

一种精简二进制代码的程序理解方法

精简二进制代码形式的软件是软件分析和程序理解需要处理的一类具有代表性的对象,基于高级语言源代码和调试符号信息的传统分析方法在处理此类软件时受到了极大限制。提出一种精简二进制形式软件的理解方法,首先将分析对象转变为运行期进程,引入实际运行中的进程信息;然后引入程序的行为特征,以程序表现出的外在行为和对外接口作为辅助信息,将此类外部特征映射到程序代码;最后基于切片思想和调试技术,获得程序切片并分析。这种方法为分析理解过程扩展了信息量,降低了复杂度,解决了分析此类软件时信息缺失和难以建立理解模型的问题。     

A parallel algorithm for generating combinations

A parallel algorithm for generating all combinations of m items out of n given items in lexicographic order is presented. The computational model is a linear systolic array consisting of m identical processing elements. It takes (_mⁿ) time-steps to generate all the (_mⁿ) combinations. Since any processing element is identical and executes the same procedure, it is suitable for VLSI implementation. Based on mathematical induction, such algorithm is proved to be correct.     

A parallel, finite-volume algorithm for large-eddy simulation of turbulent flows

A parallel, finite-volume algorithm has been developed for large-eddy simulation (LES) of compressible turbulent flows. This algorithm includes piecewise linear least-square reconstruction, trilinear finite-element interpolation, Roe flux-difference splitting (FDS), and second-order MacCormack time marching. A systematic and consistent means of evaluating the surface and volume integrals of the control volume is described. Parallel implementation is done using the message-passing programming model. To validate the numerical method for turbulence simulation, LES of fully developed turbulent flow in a square duct is performed for a Reynolds number of 320 based on the average friction velocity and the hydraulic diameter of the duct. Direct numerical simulation (DNS) results are available for this test case, and the accuracy of this algorithm for turbulence simulations can be ascertained by comparing the LES solutions with the DNS results. For the first time, a finite volume method with Roe FDS was used for LES of turbulent flow in a square duct, and the effects of grid resolution, upwind numerical dissipation, and subgrid-scale dissipation on the accuracy of the LES are examined. Comparison with DNS results shows that the standard Roe FDS adversely affects the accuracy of the turbulence simulation. For accurate turbulence simulations, only 3–5% of the standard Roe FDS dissipation is needed.