基于三线结构光的相机平面标定方法研究

相机标定技术是结构光三维视觉测量的关键技术之一,结构光测量系统的相机标定的精度对三维测量的精度有很大影响;首先对三线结构光系统图的相机标定方法进行了分析,简单介绍了工业相机成像的几何模型及标定的原理;其次利用Harris角点检测方法提取特征点坐标,并选用了BP神经网络来校正工业相机的畸变模型,以提高标定算法的优化速度和标定精度;最后采用张正友的平面标定法对校正后的摄像机模型进行标定实验,由实验结果知,该方法具有一定的准确性和有效性,在一定误差范围内,基于神经网络畸变校正的张正友相机标定能够有效提高视觉检测的精度。     

基于平面的便携式结构光系统柔性标定方法

对于便携式结构光系统, 该系统必须适合方便使用. 因此, 针对该系统的标定方法也必须采用方便且便宜的设备, 诸如具有两个或三个正交平面或者需要额外固定措施的一些设备则不宜采用. 同时针对快速三维获取的目的, 应该采用估计便携式结构光系统投影矩阵的方法. 本文针对便携式结构光系统的上述应用需求, 提出了一种基于平面的便携式结构光系统柔性标定方法. 该方法需要一个标定模板和一个参考模板. 标定模板被固定在一个平面上, 而参考模板则通过LCD投影仪被投射到该平面上. 通过交比和极几何约束, 可以获得分别对投影仪和相机的世界坐标系和图像坐标系的点对应坐标. 通过这些点对应坐标, 即可完成整个系统的标定. 实验结果表明该方法具有很高的准确性和鲁棒性．     

基于面结构光的机械工件三维扫描系统设计

针对工业机器人对自动化装配过程生产效率的提高以及工件拾取对三维扫描技术的应用需求,设计了能够准确提取机械工件表面点云的视觉系统。扫描系统主要由计算机、投影仪和工业相机构成。基于光学测量和机器视觉的原理,主要研究设计了扫描系统工业相机和投影仪的标定策略、结构光栅编码解码的检测策略以及点云重构的几何策略。对于机械工件三维扫描重构的多余背景平面点云,研究设计了通过随机选取点云并反复迭代构造背景平面实现分割的有效方法。实验结果表明采用面结构光技术,由投影仪投影不同频率的结构光栅在机械工件上,工业相机同步采集被机械工件调制的结构光栅图像,对图像中的光栅条纹进行提取并计算,并利用三角检测算法提取机械工件表面点云的方案具有高准确性,能够有效重构机械工件表面点云。     

基于误差校正的高精度三维测量系统

基于投影仪的结构光三维测量系统已得到了广泛的应用,但由于投影仪与相机的非线性特点,使用现有相位恢复算法得到的相位值具有一定的误差,影响了三维测量的精度。提出了一种基于二次型误差校正的高精度相位恢复算法。通过对标准平板进行相位恢复,分析其误差分布特征;用二次多项式对该误差进行逼近,得到误差的分布规律;根据求出的二次型误差模型对投影仪结构光系统得到的初始相位值进行修正,得到了高精度的相位恢复结果。实验表明,该算法比现有算法具有更高的相位恢复和三维测量精度。     

非对称结构相变存储单元的三维模拟与分析

文章提出一种具有非对称结构的新型相变存储器单元结构,并通过有限元方法对该非对称结构相变存储单元进行了三维电热模拟.模拟结果表明,在相同的特征尺寸下,非对称结构相变存储单元的操作电流明显小于传统的对称型T型结构相变存储单元.     

一种改进的三维人脸重构方法

提出一种改进的三维人脸重构方法。该方法采用基于单个相机的双目立体视觉系统对人脸进行采样,根据人脸对称性假设,运用补洞与纠错技术进行自动点云优化。继而采用简化的Candide-3模型作为细分初始控制网格,局部加细地进行细分曲面分层次拟合操作,采用测地线映射技术对不同表情进行归一化,并分别建立人脸数据库。实验结果表明,采用单相机立体视觉系统在提高重建精度的同时,很大程度上避免由于双相机拍摄不同步引起的重建鲁棒性降低问题。而采用细分曲面作为存储结构,在节约空间的前提下,为分层次比对筛选提供理论支持。该系统成本较低,适合在许多领域推广应用。     

一种新型红外立体视觉定位系统研究

为实现视觉目标可靠快速三维定位,设计了一种新型的基于DSP的嵌入式主动双目红外视觉系统。与普通的红外相机不同,该系统采用常规CCD相机加红外滤光片的新方法采集红外图像,通过红外滤光后的低噪声图像可以转化为低噪声二值化图像,以此提高目标定位的准确度。提出了离散化遍历视觉目标搜索算法,通过离散控制两个相机的旋转和倾斜运动,实现视觉目标快速主动遍历搜索。实验证明,该系统目标三维定位有良好的鲁棒性。     

反光和深色物体三维测量的改进方法

传统的基于结构光的三维测量方法,由于采用投射一定频率的黑白条纹式结构光栅进行测量,所以这种方法对光照和物体本身的颜色要有一定的要求。很多反光或者深色的物体均需要喷涂一定的显影剂才能完成三维形貌的测量,但对于一些特定的物体不能采用喷涂的方式。本文采用一种多次曝光的方法,在多频外差的三维测量方法基础上改进了对反光或者深色物体的三维测量,并将多次曝光和摄像机双目测量系统相结合起来进行测量。在对物体进行多次曝光之后,将多次曝光的图像融合后成为一次曝光图像。使用双目结构测量系统只对左右相机可视区域进行测量,该方法精度高、并最大程度地保留了物体上细节信息,同时提高了测量结果的完整性。     

SMT封装电路板三维在线检测技术

为了检测回流焊接之后SMT( Surface Mount Technology)封装电路板是否存在缺陷,设计并搭建了基于线结构光传感器的SMT封装电路板三维在线检测系统,通过线结构光扫描测量,获取SMT封装电路板表面三维数据。采用双传感器测量技术,有效减少数据丢失;研究了双传感器统一标定技术,可同时实现两个传感器的参数标定和坐标系统一。提出了自适应光条中心提取算法,对反射或散射影响而形成的光条图像噪声具有很好的抑制效果,能够提取准确的光条中心。实验表明系统测量精度可达到0.02 mm。系统测量得到的三维数据,可以为在线检测SMT封装电路板缺陷提供可靠的三维信息。     

气动位置伺服系统的非对称模糊PID控制

对于有杆气缸的非对称物理及摩擦力特性,提出了采用非对称模糊策略的模糊PID控制算法,较好地解决了有杆气缸由于左右两腔物理结构和摩擦力特性的不对称而造成运动过程中压力变化复杂的问题,改善了系统的动态响应性能.实验证明,采用非对称模糊策略的模糊PID控制可以明显地提高气动位置伺服系统的动态响应性能,系统具有较小的超调量和过渡过程时间,并获得了满意的重复稳态精度.     

Dense 3-D Reconstruction of an Outdoor Scene by Hundreds-Baseline Stereo Using a Hand-Held Video Camera

Three-dimensional (3-D) models of outdoor scenes are widely used for object recognition, navigation, mixed reality, and so on. Because such models are often made manually with high costs, automatic 3-D reconstruction has been widely investigated. In related work, a dense 3-D model is generated by using a stereo method. However, such approaches cannot use several hundreds images together for dense depth estimation because it is difficult to accurately calibrate a large number of cameras. In this paper, we propose a dense 3-D reconstruction method that first estimates extrinsic camera parameters of a hand-held video camera, and then reconstructs a dense 3-D model of a scene. In the first process, extrinsic camera parameters are estimated by tracking a small number of predefined markers of known 3-D positions and natural features automatically. Then, several hundreds dense depth maps obtained by multi-baseline stereo are combined together in a voxel space.So, we can acquire a dense 3-D model of the outdoor scene accurately by using several hundreds input images captured by a hand-held video camera.     

3-D shape reconstruction in an active stereo vision system using genetic algorithms

The recovery of 3-D shape information (depth) using stereo vision analysis is one of the major areas in computer vision and has given rise to a great deal of literature in the recent past. The widely known stereo vision methods are the passive stereo vision approaches that use two cameras. Obtaining 3-D information involves the identification of the corresponding 2-D points between left and right images. Most existing methods tackle this matching task from singular points, i.e. finding points in both image planes with more or less the same neighborhood characteristics. One key problem we have to solve is that we are on the first instance unable to know a priori whether a point in the first image has a correspondence or not due to surface occlusion or simply because it has been projected out of the scope of the second camera. This makes the matching process very difficult and imposes a need of an a posteriori stage to remove false matching.In this paper we are concerned with the active stereo vision systems which offer an alternative to the passive stereo vision systems. In our system, a light projector that illuminates objects to be analyzed by a pyramid-shaped laser beam replaces one of the two cameras. The projections of laser rays on the objects are detected as spots in the image. In this particular case, only one image needs to be treated, and the stereo matching problem boils down to associating the laser rays and their corresponding real spots in the 2-D image. We have expressed this problem as a minimization of a global function that we propose to perform using Genetic Algorithms (GAs). We have implemented two different algorithms: in the first, GAs are performed after a deterministic search. In the second, data is partitioned into clusters and GAs are independently applied in each cluster. In our second contribution in this paper, we have described an efficient system calibration method. Experimental results are presented to illustrate the feasibility of our approach. The proposed method yields high accuracy 3-D reconstruction even for complex objects. We conclude that GAs can effectively be applied to this matching problem.     

炸点二维坐标测量系统

笔者在文献[1]解决了因落地炸点丧失一维空间信息而无法判定二台像机上的一对成像点是否匹配的难题。本文即以此文为基础,用光轴共面且相交于一点的三台摆放均匀的像机组建一个炸点测量系统模型,从而为研制实际测量系统提供了理论依据。     

Surround structured lighting: 3-D scanning with orthographic illumination

This paper presents a new system for rapidly acquiring complete 3-D surface models using a single orthographic structured light projector, a pair of planar mirrors, and one or more synchronized cameras. Using the mirrors, we project structured light patterns that illuminate the object from all sides (not just the side of the projector) and are able to observe the object from several vantage points simultaneously. This system requires that projected planes of light to be parallel, so we construct an orthographic projector using a Fresnel lens and a commercial DLP projector. A single Gray code sequence is used to encode a set of vertically-spaced light planes within the scanning volume, and five views of the illuminated object are obtained from a single image of the planar mirrors located behind it. From each real and virtual camera we recover a dense 3-D point cloud spanning the entire object surface using traditional structured light algorithms. A key benefit of this design is to ensure that each point on the object surface can be assigned an unambiguous Gray code sequence, despite the possibility of being illuminated from multiple directions. In addition to presenting a prototype implementation, we also develop a complete set of mechanical alignment and calibration procedures for utilizing orthographic projectors in computer vision applications. As we demonstrate, the proposed system overcomes a major hurdle to achieving full 360° reconstructions using a single structured light sequence by eliminating the need for merging multiple scans or multiplexing several projectors.     

New 3-D display that can display 3-D images at long distances and that can control their 3-D positions using changing size as a cue to depth perception

This paper presents a new three-dimensional (3-D) display that can display 3-D images at long distances of tens or hundreds of meters in the depth direction and that can control their 3-D positions to meet new requirements for outdoor use. The proposed display uses changing size as a cue to depth perception, i.e., the smoothly expanding motion of virtual images formed with optical systems according to the forward movements of the users to display 3-D images at more distant positions in the depth direction than positions where virtual images are formed with optical systems because conventional 3-D displays that use binocular disparity are only able to display 3-D images at short distances in the depth direction. The feasibility of the proposed display was evaluated by subjective tests using a moving minivan in which observers viewed a test pattern that overlapped the real view ahead of the automobile observed through the windshield. The results obtained from the subjective tests revealed that the test pattern was observed at long distances over tens and hundreds of meters in the depth direction and that the position in the depth direction of the test pattern could be controlled by changing the rate at which the motion of the test pattern smoothly expanded. These results demonstrated that the proposed display was feasible.     

3-D modeling of remote dynamic situations employing mobile stereocameras

We propose a technique for 3-D modeling of objects in remote dynamic situations employing mobile stereocameras. Since the proposed technique allows independent movement of the cameras employed, 3-D modeling under various environments, such as remote places, can be realized. Our technique has an advantage over others in that camera calibration is not prerequisite to the 3-D modeling before taking images. A 3-D modeling system is described that captures images of remote objects, transfers the images by analog airwaves, and recovers the 3-D shape of the object from the images. It is expected that this technique will improve the efficiency of image information transfer. In the experiment performed, a human walking in a remote place was modeled successfully in 3-D in a laboratory by image transfer. This work was presented in part at the 11th International Symposium on Artificial Life and Robotics, Oita, Japan, January 23–25, 2006     

运动人体三维测力分析系统的设计与实现

运动人体三维测力分析系统(MBFMAS)采用并行数据采集方法,解决了三维测力平台测试过程中,测试数据的丢失问题,提高了三维测力平台的测试精度。该系统可完成数据采集,数据管理,图形显示,数据分析等功能,系统采用中文界面设计,操作简便、图形显示分辨率高,并具有监控多台三维测力平台和高速录像同步测试功能。     

序列剖面图像的三维重建和显示

本文提出了一种新的序列剖面图像三维重建和显示方法,即双目视差法。     

Analysis of Error in Depth Perception with Vergence and Spatially Varying Sensing

In stereo vision the depth of a 3-D point is estimated based on the position of its projections on the left and right images. The image plane of cameras that produces the images consists of discrete pixels. This discretization of images generates uncertainty in estimation of the depth at each 3-D point. In this paper, we investigate the effect of vergence and spatially varying resolution on the depth estimation error. First, vergence is studied when pairs of stereo images with uniform resolution are used. Then the problem is studied for a stereo system similar to that of humans, in which cameras have high resolution in the center and nonlinearly decreasing resolution toward the periphery. In this paper we are only concerned with error in depth perception, assuming that stereo matching is already done.     

Length Estimation in 3-D Using Cube Quantization

Estimators for the original length of a continuous 3-D curve given its digital representation are developed. The 2-D case has been extensively studied. The few estimators that have been suggested for 3-D curves suffer from serious drawbacks, partly due to incomplete understanding of the characteristics of digital representation schemes for 3-D curves.The selection and thorough understanding of the digital curve representation scheme is crucial to the design of 3-D length estimators. A comprehensive study on the digitization of 3-D curves was recently carried out. It was shown that grid intersect quantization and other 3-D curve discretization schemes that lead to 26-directional chain codes do not satisfy several fundamental requirements, and that cube quantization, that leads to 6-directional chain codes, should be preferred.The few 3-D length estimators that have been suggested are based on 26-directional chain coding that naturally provides a classification of the chain links, which is necessary for accurate length estimation. Cube quantization is mathematically well-behaved but the symmetry and uniformity of the 6-directional digital chain elements create a challenge in their classification for length estimation.In this paper length estimators for 3-D curves digitized using cube quantization are developed. Simple but powerful link classification criteria for 6-directional digital curves are presented. They are used to obtain unbiased length estimators, with RMS errors as low as 0.57% for randomly oriented straight lines.