Stereo and Specular Reflection

The problem of accurate depth estimation using stereo in the presence of specular reflection is addressed. Specular reflection, a fundamental and ubiquitous reflection mechanism, is viewpoint dependent and can cause large intensity differences at corresponding points, resulting in significant depth errors. We analyze the physics of specular reflection and the geometry of stereopsis which lead to a relationship between stereo vergence, surface roughness, and the likelihood of a correct match. Given a lower bound on surface roughness, an optimal binocular stereo configuration can be determined which maximizes precision in depth estimation despite specular reflection. However, surface roughness is difficult to estimate in unstructured environments. Therefore, trinocular configurations, independent of surface roughness are determined such that at each scene point visible to all sensors, at least one stereo pair can produce correct depth. We have developed a simple algorithm to reconstruct depth from the multiple stereo pairs.     

自适应窗口的时间规整立体匹配算法

针对立体视觉中图像对应点的误匹配问题,以时间规整算法(DTW)为基础,提出了自适应窗口的立体匹配算法．根据外极线的约束,在自适应窗口内采用灰度相关技术得到长度不相等的两个灰度段作为相容的匹配序列;利用动态规划法及连续性约束寻找一条最佳的匹配路径．根据回溯得到的匹配路径及其坐标值得到高密度视差图．实验结果表明,该算法具有较高的运行效率和良好的匹配效果．     

基于单相机的全向深度图获取

为了搜寻移动机器人周围最大的可通行区域,采用全向立体视觉系统,提出获取可靠的致密三维深度图方法。视觉系统由1个普通相机和2个双曲面镜组成。当系统标定后,空间点的三维坐标可以通过匹配上下镜面的成像点计算得出。匹配方法分3步：最大FX匹配,特征匹配和歧义去除。定义合适的能量函数通过动态规划来实现剩余点的匹配。实验表明该系统精度高、具有实用价值。     

基于双目视觉的深度图立体匹配算法研究改进

双目立体视觉可以直接模仿人眼与人类视觉的立体感知过程,是计算机视觉研究的核心课题之一。文章主要针对图像的立体匹配算法研究,对区域相关算法进行了分析。在传统的NCC基本灰度相关度测度函数的基础上,将动态规划优化理论引入到匹配中,提高了匹配的速度和准确度。实验表明,本文算法能够满足目标跟踪试验要求,具有重要的理论意义和较高的实用价值。     

基于模糊判别的快速图切割立体匹配

针对图切割算法存在匹配时间过长的不足,提出了一种快速的图切割立体匹配方法.选用模糊逻辑提取少量的候选匹配点,然后用这些候选匹配点构造缩减的图,再进行图切割立体匹配.采用标准图像对文中方法进行测试,并与图切割立体算法和动态规划算法进行比较的结果表明,该方法较好地保留了图切割算法匹配的准确性,而运行时间仅为图切割算法的1/35.     

自适应窗口快速立体匹配

灰度立体匹配的关键问题是选择一个合适的匹配窗口,该文对Kanade等提出的通过测算局部灰度和视差变化来选取适当窗口的方法进行了改进,提出一种仅利用灰度信息即可确定窗口的简单方法．该方法在能够求得最佳窗口的前提下,可以方便地利用整数图像来提高效率,计算量与窗口大小无关．在国际标准图像上测试的实验结果表明该方法在局部匹配方法中是最优的,虽与有些全局方法相比有一定差距,但其计算复杂度远远低于它们．     

基于双焦的单目立体成像系统分析

讨论了基于双焦的单目立体成像模型,分析了在共轴模型下CCD成像离散性而导致的深度计算误差与镜头焦距及物点空间位置的关系,当镜头焦距增加时,可精确恢复深度增大,当物点距镜头光轴距离较远,即物点位于视场边缘时,深度计算误差较小;并根据双焦成像特点提出了相应的特征匹配方法,即采用与两焦距倍数相关的特征提取算子,并对匹配结果进行相应的深度计算及插值;文章最后给出了理想双焦图像对的相应实验结果,并探讨了实验误差的形成原因。     

A Hierarchical Symmetric Stereo Algorithm Using Dynamic Programming

In this paper, a new hierarchical stereo algorithm is presented. The algorithm matches individual pixels in corresponding scanlines by minimizing a cost function. Several cost functions are compared. The algorithm achieves a tremendous gain in speed and memory requirements by implementing it hierarchically. The images are downsampled an optimal number of times and the disparity map of a lower level is used as offset disparity map at a higher level. An important contribution consists of the complexity analysis of the algorithm. It is shown that this complexity is independent of the disparityrange. This result is also used to determine the optimal number of downsample levels. This speed gain results in the ability to use more complex (compute intensive) cost functions that deliver high quality disparity maps. Another advantage of this algorithm is that cost functions can be chosen independent of the optimisation algorithm. The algorithm in this paper is symmetric, i.e. exactly the same matches are found if left and right image are swapped. Finally, the algorithm was carefully implemented so that a minimal amount of memory is used. It has proven its efficiency on large images with a high disparity range as well as its quality. Examples are given in this paper.     

立体视觉研究的进展

立体匹配是计算机视觉领域最为关键的重要分支，根据匹配基元的不同，立体视觉匹配算法可分为区域匹配、特征匹配和相位匹配三大类。该文对三类匹配算法进行了详细的评述，包括它们的理论依据、基本特征和改进策略。     

Trinocular Stereo Using Shortest Paths and the Ordering Constraint

This paper describes a new algorithm for disparity estimation using trinocular stereo. The three cameras are placed in a right angled configuration. A graph is then constructed whose nodes represent the individual pixels and whose edges are along the epipolar lines. Using the well known uniqueness and ordering constraint for pair by pair matches simultaneously, a path with the least matching cost is found using dynamic programming and the disparity filled along the path. This process is repeated iteratively until the disparity at all the pixels are filled up. To demonstrate the effectiveness of our approach, we present results from real world images and compare it with the traditional line by line stereo using dynamic programming.     

图像立体匹配研究进展

图像的立体匹配一直是立体视觉的研究重点.首先简要介绍了立体匹配方法及其分类,归纳了立体匹配中的各种约束条件和相似性测度函数;然后总结了局部匹配算法和全局匹配算法的特点,并结合对象的三维重建问题重点分析了全局匹配算法中的动态规划算法、图割法和置信度传播算法;最后对立体匹配研究面临的主要问题给出了一些建议.     

一种改进的立体像对密集点匹配算法

文中研究在随机光场照射下基于窗口的密集点匹配算法。针对基于窗口匹配中出现的细节平滑问题,提出了在窗口内对像素点引入权值参数来提高细节部分测量精度的方法。在匹配前对图像进行校正,使得各极线和图像坐标系的横轴平行,在匹配过程中不需要再计算极线方程,大大提高了匹配的效率。根据待匹配图像的灰度信息和摄像机的内外参数信息,通过求解对应窗口内像素点向量夹角的方式进行双目立体匹配。在试验中,完成了棋盘格图像的密集点匹配,并与典型区域匹配算法进行了匹配效率与视差图效果的对比分析,验证了文中算法在匹配效率和视差图效果方面的优越性。     

一种改进的立体视觉匹配算法*

针对目前双目立体视觉匹配算法匹配误匹配率高的问题,提出了一种具有尺度不变特性的 Harris检测算法,将SIFT特征描述子引入到Harris特征的描述过程当中,使其提取到的特征具有旋转、尺度、亮度不变性。并且为了提高匹配精度,采用RANSAC法去除误匹配来降低误匹配率。相对于经典的 Harris算法,该算法提取的特征具有尺度不变特性且误匹配率降低,是一种有效可行的立体匹配算法。     

Stereo vision correspondence using a multichannel graph matching technique

A multichannel feature-based stereo vision technique is described in this paper where curve segments are used as the feature primitives in the matching process. Curve segments are extracted by tracking the zero-crossings of the left and right images. The generalized Hough transform of each curve and the curve length are used as a local feature vector in representing the distinctive characteristics of the curve segment. The feature vector of each curve segment in the left image is used as a constraint to find an instance of the same curve segment in the right image. The epipolar constraint on the centroids of the curve segment is used to limit the searching space in the right image.

A relational graph is formed from the left image by treating the centroids of the curve segments as the nodes of the graph. The local features of the curve segments are used to represent the local properties of the nodes, and the relationship between the nodes represents the structural properties of the objects in the scene. A similar graph is also formed from the right image curve segments. A graph isomorphism is then formed between the two graphs by using the epipolar constraint on the centroids, the local properties of the nodes, node assignment and the structural relationship (compatibility) between the nodes.     

基于双序列比对算法的立体图像匹配方法*

在分析现有立体匹配方法的基础上,提出一种基于双序列比对算法的立体图像匹配方法。将立体图像对中同名极线上的像素灰度值看做是一对字符序列,使用基于动态规划思想的双序列比对算法对这些对字符序列进行匹配,以获取立体图像视差。为验证该方法的可行性和适用性,采用人脸立体图像对进行实验。实验结果表明,使用该方法进行立体图像匹配能获得光滑的、稠密的视差图。基于动态规划思想的双序列比对算法能够有效地解决立体图像匹配问题,从而为图像的立体匹配提供了一个实用有效的方法。     

基于立体视觉的多摄像位空间定位系统研究

基于多摄像位的空间定位系统主要由摄像机标定、立体匹配、基于点的三维重建三个部分构成,主要围绕这三个部分对空间定位系统进行研究.首先,本文采用基于平面标定模板的摄像机标定方法,通过实验和计算来获取摄像机的参数,实现对摄像机参数的标定.其次,使用Birchfield算法研究该系统的立体匹配环节,试验结果得到了视差图.最后,...     

一种测量高光物体的双目Helmholtz立体视觉方法

提出了一种基于迭代动态规划的双目Helmholtz立体视觉算法,并将其应用于高光物体的测量。算法首先对获取的Helmholtz图像对作图像校正,然后确定扫描线的端点,最后设计了一种迭代动态规划方法建立匹配获取视差图,从而恢复出高光物体的表面深度。实验采用光线跟踪方法获取带有高光的双目Helmholtz图像,视差图结果表明该方法能够有效地恢复出高光物体的深度信息。     

基于梯度值的自适应窗口立体图像匹配算法

针对基于区域的立体图像匹配算法支持窗口难以选择,容易出现窗口过大或过小的问题,提出一种新的自适应窗口立体图像匹配算法。该算法利用Sobel梯度算子计算像素梯度值,并根据其梯度值动态地获取具有自适应的支持窗口,然后分别选择相似性测度函数SAD或NCC搜索最佳匹配点,获得视差图。此外,算法在窗口选择过程中进行优化,减少了计算量。实验结果表明,改进后的算法提高了匹配正确率且计算时间缩短了近5%。     

基于立体视觉的高光物体恢复深度图的方法

基于立体视觉的物体深度图提取,在工业检测等许多方面均有较高的应用价值,但对于工程领域里的高光物体带来的误差,研究不多。为了较好地恢复具有高光反射的物体表面的三维深度信息,论文提出一种与立体视觉结合的多光源法去除高光的技术,使得后续的立体匹配更加可靠,深度计算更加准确。实验首先采用多光源法获取高光反射物体的多组图像,再经过图像预处理、摄像机标定、高光去除、立体匹配等步骤,结果证明这种方法有效地恢复了具有相对大面积的高光区域表面的物体的三维深度信息。     

基于控制点的分层双向动态规划立体匹配算法

提出一种基于控制点的分层双向动态规划立体匹配算法．首先,利用改进Volumetric迭代算法获取具有高可靠度的控制点,将其作为具有正确视差的匹配点．其次,在高可靠度控制点的指导下,利用分层双向动态规划算法在DSI（disparity-space image）视差空间图中进行初匹配,进而在Delta DSI（delta disparity-space image）视差变化空间图中进行精匹配,从而获取高密度视差图．实验结果表明,该算法不仅可以改善传统直接动态规划立体匹配算法产生的带状条纹瑕疵,而且计算速度较快,匹配结果也优于传统动态规划的匹配结果．