Registering coronal histological 2-D sections of a rat brain with coronal sections of a 3-D brain atlas using geometric curve invariants and B-spline representation

A new approach is proposed for registering a set of histological coronal two-dimensional images of a rat brain sectional material with coronal sections of a three-dimensional brain atlas, an intrinsic step and a significant challenge to current efforts in brain mapping and multimodal fusion of experimental data. The alignment problem is based on matching external contours of the brain sections, and operates in the presence of tissue distortion and tears which are routinely encountered, and possible scale, rotation, and shear changes (the affine and weak perspective groups). It is based on a novel set of local absolute affine invariants derived from the set of ordered inflection points on the external contour represented by a cubic B-spline curve. The inflection points are local intrinsic geometric features, which are preserved under both the affine and the weak perspective transformations. The invariants are constructed from the sequence of area patches bounded by the contour and the line connecting two consecutive inflection points, and hence do make direct use of the area (volume) invariance property associated with the affine transformation. These local absolute invariants are very well suited to handle the tissue distortion and tears (occlusion problem).     

基于特征数不变量的插针特征点匹配算法研究

针对电连接器插针匹配过程中特征点存在的近似对称以及在不同图像间存在大角度旋转变换的问题,提出了一种基于六点特征数不变量的特征点匹配算法。将特征点分为凸包与内点两部分,利用凸包上的点在射影变换中排列顺序的不变性实现了凸包匹配,利用以凸包特征点为基准的内点特征向量的相似性实现了内点匹配。实验结果证明,提出的算法能够很好地实现对插针特征点的匹配,具有一定的鲁棒性。     

一种给定平面点集凸壳算法

凸壳问题是计算机图形学、图像处理、模式识别等众多领域中的一个基本问题。将正切线算法应用到给定平面点集凸壳的计算中,并实现了正切线算法中新加入点的自动编号。通过极值点把点集分成若干个区域,对于点集中的每一个点,若落于中间区域,则淘汰掉该点;若落于其它区域,则通过该点与它所在区域的原单调段进行计算得到新单调段,从而得到给定平面点集的凸壳。算法效率高,在最坏情况下的时间复杂度为O(nlogm),m为凸壳的顶点数。     

一种新的适合于目标识别的仿射不变量

针对仿射变换所造成的某些特征点提取不稳定,提出一种新的适合于目标识别的仿射不变量,它是基于特征点和几乎不受仿射变换影响的目标轮廓线．当目标无遮挡时,新不变量仅依赖于当前特征点和整个轮廓线;当目标有遮挡时,新不变量依赖于当前特征点、与它直接相邻的两个特征点以及它们之间的轮廓线．在已有的基于特征点的仿射不变量中,新不变量所依赖的特征点是最少的,可以很好地应用于特征点提取不稳定场合的目标识别．     

采用热核特征的SAR图像目标识别

为了解决SAR图像受相干斑噪声干扰和震后发生形变而识别率偏低的问题,提出了一种新的仿射、形变不变特征-热核特征,并将该特征用于SAR图像目标识别.首先采用推广的核模糊C-均值方法分割SAR图像,提取SAR图像目标形状;接着对目标形状进行Delaunay三角剖分,采用余切权重法对Laplace-Beltrami Operator离散化,通过离散化Laplace-Beltrami Operator特征值、特征向量求每一点热核特征;然后采用谱距离公式对点点间热核距离计算,转化为距离分布表示目标形状的热核特征;最后采用L1相似性准则对图像进行相似性度量,得到识别结果.实验表明:与经典的Hu不变矩方法相比,对于仿射变换和发生形变的SAR图像,该方法都具有更高的识别率.因此,基于热核特征的SAR图像识别方法是一种更加有效的识别方法.     

基于组合矩的激光雷达距离像目标识别

激光成像雷达距离像与目标表面物理结构特性密切相关,体现目标的本质特征,是目标识别的主要研究方向。采用组合矩的神经网络方法进行了相干激光雷达距离像目标识别仿真研究。用Hu不变矩和仿射不变矩两者的低阶矩组合表示距离像目标区域特征,利用反向传播(BP)神经网络识别不同方位角的车辆。当视场角不变时,训练10个目标,每个目标取3～19个样本,在不同载噪比(CNR)情况下,分析Hu不变矩、仿射不变矩和两者组合矩的识别率。理论分析和仿真实验表明利用组合不变矩进行距离像目标识别性能优于单独利用其中一种不变矩。     

一种3D眼镜虚拟试戴系统的实现

针对人脸图像试戴3D眼镜过程中存在的镜腿遮挡人脸问题,文中提出一种基于人脸图像的3D眼镜虚拟试戴技术。利用构建的人脸形状的三维模型,使其在虚拟试戴中对镜腿起到消隐作用,解决镜腿的遮挡问题。文中对输入的人脸图像进行关键点检测,结合Graham扫描法求得人脸形状的凸多边形,利用平移扫描构建人脸形状的三维模型。此外,文中根据定位人脸图像上的关键点以及姿态估计后对三维眼镜模型的变换,将眼镜模型佩戴到人脸图像上。实验结果表明,该方法对于多视角的人脸图像实现了虚拟试戴效果,解决了多种视角下人脸图像试戴过程中镜腿的遮挡问题,虚拟试戴中镜腿遮挡平均准确率为94.5%,遮挡精度较高。     

面向指背关节纹识别的图像集与凸壳优化算法

本文将指背关节纹作为生物特征识别对象,提出了基于图像集与凸壳优化模型的指背关节识别算法。所提算法以指背关节纹图像集作为输入,并将局部相位特征方法用于指背关节纹特征提取,进而寻求适用于指背关节纹识别的凸壳优化模型,研究凸壳模型的构建方法并对其进行优化,从而完成指背关节纹的识别。仿真实验表明,所提算法在公开的指背关节纹中,均取得了不错的识别结果。      

Local hull-based surface construction of volumetric data from silhouettes

The marching cubes (MC) is a general method which can construct a surface of an object from its volumetric data generated using a shape from silhouette method. Although MC is efficient and straightforward to implement, a MC surface may have discontinuity even though the volumetric data is continuous. This is because surface construction is more sensitive to image noise than the construction of volumetric data. To address this problem, we propose a surface construction algorithm which aggregates local surfaces constructed by the 3-D convex hull algorithm. Thus, the proposed method initially classifies local convexities from imperfect MC vertices based on sliced volumetric data. Experimental results show that continuous surfaces are obtained from imperfect silhouette images of both convex and nonconvex objects.     

基于广义典型相关分析的仿射不变特征提取方法

该文结合广义典型相关分析(GCCA)理论,提出了一种新的图像仿射不变特征提取方法。首先,基于多尺度自卷积变换(MSA)构造了一组新的变换量多尺度自卷积熵(MSAE)。然后证明了该熵具有仿射不变性;再利用GCCA将MSA和MSAE变换值作为两种特征进行融合,得到具有更丰富图像信息的组合特征。最后利用MSA,MSAE和组合特征,结合最近距离分类器分别对视点变换图像以及加噪声、加部分遮挡视点变换图像进行分类识别实验。结果表明,组合特征得到了最高的正确识别率,MSAE次之,MSA最低。     

基于透视不变二值特征描述子的图像匹配算法

针对基于局部特征的图像匹配算法普遍存在对透视变换顽健性差的缺点,提出了一种新的二值特征描述子PIBC（perspective invariant binary code）,提高了图像匹配算法的透视变换顽健性。首先,在提取金字塔图像FAST特征点的基础上,利用Harris角点响应值去除非极大值点和边缘响应点;其次,通过模拟相机不同视角成像之间的透视变换,对单个FAST特征点生成不同视角变换下图像的二值描述子,使描述子具备描述不同视角图像中同一特征点的能力。实验结果表明,算法在提高描述子透视不变性的同时时间复杂度与SURF算法近似。     

基于点不变特征的亚像素级图像配准技术

图像匹配是图像处理和计算机视觉领域的一个基础问题,它源自多个方面的实际问题.点特征匹配的首要任务就是提取稳定的特征,并进行描述.该特征能对旋转、尺度缩放、仿射变换、视角变化、光照变化等图像变化因素保持一定的不变性,而对物体运动、遮挡、噪声等因素也保持较好的可匹配性.提出一种基于点的尺度、旋转不变特征变换（SIFT）算法的亚像素级图像配准算法,首先在尺度空间进行特征检测,并确定关键点的位置和关键点所处的尺度,然后使用关键点邻域梯度的主方向作为该点的方向特征,以实现算子对尺度和方向的无关性.该方法具有旋转、尺度缩放、亮度变化不变性,对视角变化、仿射变换、噪声也保持一定程度的稳定.独特性好,信息量丰富,适用于在海量特征数据库中进行快速、准确的匹配.高速性,该匹配算法可以达到实时的要求.     

基于差分进化算法和遗传算法的混合优化 算法及其在阵列天线方向图综合中的应用

阵列天线方向图综合作为智能天线的一项重要技术对于复杂系统的优化问题提出了更高的要求.本文结合差分进化的基本思想和遗传算法的基因交叉和变异方法构建了一种新的混合优化方法.该算法使用差分进化算子作为主要优化手段,结合遗传算法优胜劣汰的基本思想以及其中的交叉和变异方法,通过融合两种优化方法各自的优点,可以显著改善多参数、高度非线性问题的优化结果、提高计算效率.计算机仿真结果表明,与现有算法相比,该算法用于天线方向图综合具有收敛速度快、优化能力强、算法可靠等优势.     

连接向量特征匹配的暗场图像配准方法

利用损伤点之间的位置关系,根据光学元件损伤暗场图像的特点设计了一种基于连接向量特征匹配的配准方法。该方法首先对基准图像及待配准图像分别进行图像预处理,提取损伤点轮廓的中心坐标作为损伤点的位置值。然后构建损伤点连接向量,求出主方向并计算主方向下的连接向量特征,使用连接向量匹配获得匹配点对,最后利用RANSAC算法对匹配点对进行仿射变换参数计算。该方法具有旋转不变性,尺度不变性以及较高的配准准确度。实验对比分析了该方法与SIFT算法的计算效率及配准精度,结果表明在暗场图像条件下文中方法更有效且为背景单一,灰度信息较少同时要求较高的配准速度的场景下的图像配准问题提供了解决方案。     

Affine invariance contour descriptor based on iso-area normalisation

In pattern recognition, by observing a contour extracted from a shape, the position of the points of this contour can be normalised by using a set of triangles with the same area whose vertices consist of the centroid of the contour and a pair of successive points on the contour. Contour characterisation can be obtained by lowpass filtering and observing the resulting changes in the areas of the triangles. It is proved that, for a filtered contour, the areas of the triangles are linear under affine transforms. The experimental results show that the approach is resistant to affine transformations and noise     

基于SIFT的边缘局部仿射的图像拼接算法

本文针对累计误差形成的多幅图像拼接产生畸变的问题,提出了一种基于边缘局部仿射的拼接算法,在拼接过程中逐步衰减仿射变换,使得图像在拼接过程中逐渐降低过仿射带来的畸变.同时为从视觉上分析图像拼接过程特征点的变化情况,本文还提出了一种基于特征点的骨架图算法,通过拼接后骨架图的图像来分析各种拼接算法.可以广泛应用于拼接算法的测试过程.     

Gradient of reference difference based matching algorithm for image feature point

During matching on feature point, gray correlation matching technology is utilized to extract multi-peaks as a coarse matching set. A pair of given corresponding reference points within the left and right images is used to calculate gradients of reference difference between the reference points and each feature point within the multi-peaks set. The unique correspondence is determined by criterion of minimal gradients of reference difference. The obtained correspondence is taken as a new pair of reference points to update the reference points continuously until all feature points in the left (or right) image being matched with the right (or left) image. The gradients of reference difference can be calculated easily by means of pre-setting a pair of obvious feature points in the left and right images as a pair of corresponding reference points. Besides,the efficiency of matching can be improved greatly by taking the obtained matching point as a new pair of reference points, and by updating the reference point continuously. It is proved that the proposed algorithm is valid and reliable by 3D reconstruction on two pairs of actual natural images with abundant and weak texture, respectively.     

Two Related Problems of Redundancy Reduction in Data Representation by Means of Convex Polyhedra

Two problems of data representation by means of convex polyhedra are considered. In the first problem, it is required to exclude from a finite set of points X the points that are not vertices of the convex hull of X. An algorithm based on solving a series of linear programming problems is developed. Its computational complexity is asymptotically lower than the complexity of a convex hull constructing, and it requires much less additional memory than for constructing a convex hull. The second problem consists in finding the minimal subset of inequalities in a system of linear inequalities whose solution set coincides with the solution set of the initial system. It is shown that this problem can be solved similarly to the first one, and the solution algorithm can be extended to the case of nonlinear inequalities. Randomized improved versions of both algorithms are proposed.     

Automatic registration and alignment on a template of cardiacstress and rest reoriented SPECT images

Single photon emission computed tomography (SPECT) imaging with ²⁰¹Tl or ^99mTc agent is used to assess the location or the extent of myocardial infarction or ischemia. A method is proposed to decrease the effect of operator variability in the visual or quantitative interpretation of scintigraphic myocardial perfusion studies. To effect this, the patient's myocardial images (target cases) are registered automatically over a template image, utilizing a nonrigid transformation. The intermediate steps are: 1) Extraction of feature points in both stress and rest three-dimensional (3-D) images. The images are resampled in a polar geometry to detect edge points, which in turn are filtered by the use of a priori constraints. The remaining feature points are assumed to be points on the edges of the left ventricular myocardium. 2) Registration of stress and rest images with a global affine transformation. The matching method is an adaptation of the iterative closest point algorithm. 3) Registration and morphological matching of both stress and rest images on a template using a nonrigid local spline transformation following a global affine transformation. 4) Resampling of both stress and rest images in the geometry of the template. Optimization of the method was performed on a database of 40 pairs of stress and rest images selected to obtain a wide variation of images and abnormalities. Further testing was performed on 250 cases selected from the same database on the basis of the availability of angiographic results and patient stratification     

基于双向邻域过滤策略的图形匹配类遥感图像配准算法

针对遥感图像由于较大仿射变换关系、相似图案和多源性等导致图形匹配时出现伪同构现象,提出了一种基于双向邻域过滤策略的图形匹配方法.本方法采用双向邻域的图形特征描述子来表示特征点的邻域关系.当误配点的双向邻域任意顶点在后期迭代中被视为误配点时,将与匹配点集具有稳定双向邻域结构的点恢复至匹配点集,同时剔除伪同构中残留的误配点.通过与Random Sample Consensus(RANSAC)、Graphing Transformation Matching(GTM)算法以及提出的双向邻域匹配方式比较得出,基于双向邻域过滤策略的匹配方式能够处理空间顺序匹配时存在的伪同构问题,同时获得更高的召回率和匹配率.