Search strategies for shape regularized active contour

Nonlinear shape models have been shown to improve the robustness and flexibility of contour-based object segmentation when there are appearance ambiguities between the object and the background. In this paper, we focus on a new search strategy for the shape regularized active contour (ShRAC) model, which adopts existing nonlinear shape models to segment objects that are similar to a set of training shapes. The search for optimal contour is performed by a coarse-to-fine algorithm that iterates between combinatorial search and gradient-based local optimization. First, multi-solution dynamic programming (MSDP) is used to generate initial candidates by minimizing only the image energy. In the second step, a combination of image energy and shape energy is minimized starting from these initial candidates using a local optimization method and the best one is selected. To generate diverse initial candidates while reducing invalid shapes, we apply two pruning methods to the search space of MSDP. Our search strategy combines the advantages of global combinatorial search and local optimization, and has shown excellent robustness to local minima caused by distracting suboptimal solutions. Experimental results on segmentation of different anatomical structures using ShRAC, as well as preliminary results on human silhouette segmentation are provided.     

A background robust active appearance model using active contour technique

This paper proposes an active contour-based active appearance model (AAM) that is robust to a cluttered background and a large motion. The proposed AAM fitting algorithm consists of two alternating procedures: active contour fitting to find the contour sample that best fits the face image and then the active appearance model fitting over the best selected contour. We also suggest an effective fitness function for fitting the contour samples to the face boundary in the active contour technique; this function defines the quality of fitness in terms of the strength and/or the length of edge features. Experimental results show that the proposed active contour-based AAM provides better accuracy and convergence characteristics in terms of RMS error and convergence rate than the existing robust AAM. The combination of the existing robust AAM and the proposed active contour-based AAM (AC-R-AAM) had the best accuracy and convergence performances.     

基于Snake模型的快速目标检测算法的研究与仿真

该文提出了一种基于Snake模型的快速目标检测算法,可以实现图象全空域有效搜索。为了能够在实时图象处理系统中获得应用,该算法主要针对简单离散Snake模型进行改进。利用图象区域分割,并设置适当的目标判别方法,经有限次迭代之后能够有效地收敛到目标,并且对处于相邻图象块中的同一目标能进行自动合并。仿真结果表明：该算法即使在目标与背景的对比度很低的情况下也能有效地检测到目标。     

An improved time-adaptive self-organizing map for high-speed shape modeling

In this paper, an improved active contour model based on the time-adaptive self-organizing map with a high convergence speed and low computational complexity is proposed. For this purpose, the active contour model based on the original time-adaptive self-organizing map is modified in two ways: adaptation of the speed parameter and reduction of the number of neurons. By adapting the speed parameter, the neuron motion speed is determined based on the distance of each neuron from the shape boundary which results in an increase in the speed of convergence of the contour. Using a smaller number of neurons, the computational complexity is reduced. To achieve this, the number of neurons used in the contour is determined based on the boundary curvature. The proposed model is studied and compared with the original time-adaptive self-organizing map. Both models are used in several experiments including a tracking application. Results reveal the higher speed and very good performance of the proposed model for real-time applications.     

A Modified Fourier–Galerkin Method for the Poisson and Helmholtz Equations

In this paper we present a modified Fourier–Galerkin method for the numerical solution of the Poisson and Helmholtz equations in a d-dimensional box. The inversion of the differential operators requires O(N ^d ) operations, where N ^d is the number of unknowns. The total cost of the presented algorithms is O(N ^d :log₂:N), due to the application of the Fast Fourier Transform (FFT) at the preprocessing stage. The method is based on an extension of the Fourier spaces by adding appropriate functions. Utilizing suitable bilinear forms, approximate projections onto these extended spaces give rapidly converging and highly accurate series expansions.     

Human facial feature extraction for face interpretation and recognition

Facial features' extraction algorithms which can be used for automated visual interpretation and recognition of human faces are presented. Here, we can capture the contours of the eye and mouth by a deformable template model because of their analytically describable shapes. However, the shapes of the eyebrow, nostril and face are difficult to model using a deformable template. We extract them by using an active contour model (snake). In the experiments, 12 models are photographed, and the feature contours are extracted for each portrait.     

基于求解泊松方程和梯度的图像修复的研究

提出了一种基于梯度的新的图像修复算法从图片或照片上面去除有影响的物体。文中的方法是分两个阶段来重建移除的区域：移除区域的梯度通过填充算法来填充;通过解泊松方程在梯度映射下来重构图像。在填充梯度的方法中提出了一个新的补丁匹配标准。在这个标准中,同时用到梯度和颜色信息,所以,有一个好的图像修复结果。文中用一些修复例子和结果进行比较,来演示本方法的优越性。     

Parallel FFT-based Poisson solver for isolated three-dimensional systems

We describe an implementation to solve Poisson?s equation for an isolated system on a unigrid mesh using FFTs. The method solves the equation globally on mesh blocks distributed across multiple processes on a distributed-memory parallel computer. Test results to demonstrate the convergence and scaling properties of the implementation are presented. The solver is offered to interested users as the library PSPFFT.

Program summary

Program title: PSPFFTCatalogue identifier: AEJK_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEJK_v1_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 110 243No. of bytes in distributed program, including test data, etc.: 16 332 181Distribution format: tar.gzProgramming language: Fortran 95Computer: Any architecture with a Fortran 95 compiler, distributed memory clustersOperating system: Linux, UnixHas the code been vectorized or parallelized?: Yes, using MPI. An arbitrary number of processors may be used (subject to some constraints). The program has been tested on from 1 up to ∼ 13 000 processors. RAM: Depends on the problem size, approximately 170 MBytes for 48³ cells per process.Classification: 4.3, 6.5External routines: MPI (http://www.mcs.anl.gov/mpi/), FFTW (http://www.fftw.org), Silo (https://wci.llnl.gov/codes/silo/) (only necessary for running test problem).Nature of problem: Solving Poisson?s equation globally on unigrid mesh distributed across multiple processes on distributed memory system.Solution method: Numerical solution using multidimensional discrete Fourier Transform in a parallel Fortran 95 code.Unusual features: This code can be compiled as a library to be readily linked and used as a blackbox Poisson solver with other codes.Running time: Depends on the size of the problem, but typically less than 1 second per solve.     

Active shape from stereo for highway inspection

Abstract. This paper describes an unsupervised algorithm for estimating the 3D profile of potholes in the highway surface, using structured illumination. Structured light is used to accelerate computation and to simplify the estimation of range. A low-resolution edge map is generated so that further processing may be focused on relevant regions of interest. Edge points in each region of interest are used to initialise open, active contour models, which are propagated and refined, via a pyramid, to a higher resolution. At each resolution, internal and external constraints are applied to a snake; the internal constraint is a smoothness function and the external one is a maximum-likelihood estimate of the grey-level response at the edge of each light stripe. Results of a provisional evaluation study indicate that this automated procedure provides estimates of pothole dimension suitable for use in a first, screening, assessment of highway condition. Received: 9 October 1998 / Accepted: 22 February 2000     

货车车钩铸件表面细沙的图像处理分析方法

目前,车钩的清理工作主要采用传统的人力来完成,大量的粉尘使得人们的健康出现问题以及整个作业的难度加大,即耗时又有害健康,因此利用机器人代替人类进行清砂的方式获得广泛研究。机器人利用眼睛观测事物,找到表面的细沙部分,即利用视觉检测方法进行清砂过程。采用线性CCD、摄像头组成图像的采集单元,提出了一种最优外部轮廓检测方法,计算出外部轮廓特征,从而找到最优的清除方法。仿真分析结合实验表明,最优的外部轮廓检测方法对于清砂处理具有合理性和高效性。     

细节保持的曲面浅浮雕算法

为保持曲面浮雕的细节特征,改善浮雕与背景曲面的过渡效果,提出一种细节保持的曲面浮雕算法.首先采用Canny算子在梯度域定位内外轮廓,获得连续的梯度域;其次提出非线性函数,并用其压缩梯度幅值实现形状压缩;再通过双边滤波算子来保持和增强浮雕细节;最终通过求解积分方程重建曲面浮雕.该算法将背景曲面作为积分方程的优化条件,使浮雕在轮廓处向曲面光滑过渡;在重建过程中利用Fourier变换的微分性质在频域实现方程的精确求解,无需设置迭代收敛条件;通过调整参数可方便地控制浮雕整体变化范围、细节锐化程度以及浮雕与背景曲面的过渡效果.实验结果表明,文中算法参数的几何意义直观,所得曲面浮雕细节清晰,边界过渡自然.     

A unified method for appearance and geometry completion of point set surfaces

This paper presents a novel approach for appearance and geometry completion over point-sampled geometry. Based on the result of surface clustering and a given texture sample, we define a global texture energy function on the point set surface for direct texture synthesis. The color texture completion is performed by minimizing a constrained global energy using the existing surface texture on the surface as the input texture sample. We convert the problem of context-based geometry completion into a task of texture completion on the surface. The geometric detail is then peeled and converted into a piece of signed gray-scale texture on the base surface of the point set surface. We fill the holes on the base surface by smoothed extrapolation and the geometric details over these patches are reconstructed by a process of gray-scale texture completion. Experiments show that our method is flexible, efficient and easy to implement. It provides a practical texture synthesis and geometry completion tool for 3D point set surfaces.     

一种新的快速复杂连通区域扫描线填充算法

提出一种快速求取扫描线与轮廓线交点的算法,只需遍历2次轮廓线即可求得所有交点,显著降低了算法复杂度。基于该求交算法得到的扫描线填充算法,可以填充任意的复杂连通区域。与同类算法犤2,4,5犦相比,该文算法流程简单,填充速度快。     

Application of the Galerkin and Least-Squares Finite Element Methods in the solution of 3D Poisson and Helmholtz equations

This paper presents the numerical solution, by the Galerkin and Least Squares Finite Element Methods, of the three-dimensional Poisson and Helmholtz equations, representing heat diffusion in solids. For the two applications proposed, the analytical solutions found in the literature review were used to compare with the numerical solutions. The analysis of results was made from the L₂ norm (average error throughout the domain) and L_∞ norm (maximum error in the entire domain). The results of the two applications (Poisson and Helmholtz equations) are presented and discussed for testing of the efficiency of the methods.     

基于边界跟踪的任意形状区域填充算法

针对任意形状的多边形及孔洞区域,提出基于边界跟踪的填充算法。用细化算法对图像进行单线化预处理,分别跟踪各个封闭曲线的边界,从第1个边界点坐标出发,根据跟踪方向对每个边界点进行有向直线填充,遇到边界点时停止,将各填充图与原图进行合并。实验结果表明,该算法不受图形边界状况和自身形状的影响,能适应任意类型的封闭区域;沿边界点进行处理,避免了对背景点的重复计算;对于多孔洞的封闭图形,能对各个孔洞进行独立处理,可灵活选择填充效果。     

视频图像活动轮廓目标检测跟踪研究

研究视频图像目标跟踪定位精确度问题。由于在图像中通常会发生缩放,造成图像目标模糊不清。传统的目标跟踪算法该类算法仅以目标发生平移运动为假设前提,图像质量差。为解决上述问题,提出了一种活动轮廓目标跟踪定位检测算法。首先选择合适的滑窗,采用减背景法来确定视频对象的运动区域,采用卡尔曼形态滤波来消除残余的噪声,然后针对目标在活动轮廓局部内具有较高灰度值的特征,通过自适应阈值来判别滑窗中心位置是否存在目标。当滑窗遍历整幅图像后,就可以得到目标的定位结果。仿真结果表明,改进算法不仅能够消除差分图像中的显露背景,从而得到运动视频对象精确的轮廓,并且可进行多目标的分割与跟踪,具有一定的实际应用价值。     

An algorithm for filling complex holes in reverse engineering

The existence of holes in meshes makes it difficult for mesh operations, especially when comes to model rebuilding, rapid prototyping and finite element analysis. Existing hole-filling algorithms are capable of filling holes on small and smooth regions of a model. For large holes with complex boundaries or in curved region, they may not result in satisfactory results. This paper proposes an algorithm which first split the holes into flatter ones and then split the complex holes based the concept of edge expansion. It incrementally splits a complex hole into simple ones by respecting the 3D shape of its boundary and the neighboring meshes, and then fills each resulting simple hole with planar triangulation. The proposed algorithm works well for a variety of complex holes and can better preserve the detailed features of the original mesh.     

基于时空图的轮廓线模型研究

主动轮廓线模型(Snakes)具有能够结合先验知识和图像特征的理论价值,但由于能量局部极值问题的困扰,而鲜已用于实际问题。前人通过改进优化算法来提高其分割效果。文章则尝试从Snakes的外部力入手,引入时空图的光流特征,通过改造能量函数提高分割效果。实验对比验证在复杂背景下,基于时空图的轮廓线模型依然可以有效跟踪运动物体,此时普通Snakes模型必须做大量手动调整。而它同时也解决了帧差等视频分割方法难于识别、提取目标轮廓的问题。时空图轮廓线模型抓住了运动目标的图像特征,在简单的优化算法下依然可以得到较好的分割效果,可以用实时系统。     

Automatic extraction of face contours in images and videos

The paper proposed an automatic and accurate extraction of the human face contour algorithm. Because a human face contour includes very important facial features to identifying or verifying a person, the accuracy of face contour extraction influences performance of face recognition. The automatic extraction human face contour algorithm includes a novel flowchart for improving accuracy of face contours extraction. To obtain the edge map of a face contour, the divided-and-conquer technique and Canny edge detector were used to avoid the features in the central part of face. The genetic algorithm is implemented to automatically find the parameters of Canny edge detector. Finally, the Poisson gradient vector flow (PGVF) active contour model used the edge map to extract face contours. Three datasets with temporal sequence images were tested for evaluation of the proposed algorithm. The experimental results demonstrated that the algorithm obtained accurate face contours.