结构光三维测量系统中投影仪标定技术研究

投影仪标定是单摄像机单投影仪结构光三维测量中的基础。采用双面标定块实现投影仪的标定。标定块正面为黑底白色圆点图案,通过Tsai两步法及非线性优化完成摄像机标定。背面为反射率均匀的白色平面,由投影仪投影双方向高亮度的直线来生成特征点。针对特征点三维坐标难以确定的问题,采用了两种方法:一是依靠摄像机标定结果;二是结合正面圆点图案,利用交比不变性获取更多的有效输入数据。标定设备简单,操作方便。实验结果证明具有较理想的标定精度。     

单周期条纹双四步相移投影仪的标定方法

针对投影仪标定方法中存在畸变及倾斜投影引起条纹周期、条纹级数变化的问题,提出一种单周期条纹双四步相移投影仪的标定方法.设计生成横向和纵向各两组单周期条纹图像,经投影仪投影到带有圆形标识的标定板上,相机同步采集标定板图像,叠加由双四步相移获得的两幅相位主值图,对叠加相位主值图相位展开,利用展开的绝对相位值计算投影仪像素坐标值,最终将投影仪标定转换为成熟的相机标定.实验结果表明:仿真投影仪标定实验准确度的最大重投影误差约为0.4pixel,均方根误差为0.132 96pixel;实际投影仪标定实验准确度的最大反投影误差约为0.46pixel,均方根误差为0.143 12pixel;实验结果与仿真结果的最大反投影误差相差15%,均方根误差相差7.6%.与现有的采用三频相位展开进行投影仪标定的方法相比,投影光栅图像数可减少8幅.该方法改善了现有投影仪标定方法的不足,标定准确度和标定效率均得到提高.     

光栅投影三维测量系统标定技术研究

相机与投影仪的标定是影响光栅投影三维测量系统精度的因素之一,且标定所得参数的精度直接影响系统的测量精度。分析标志点边缘成像时的退化模型,提出了基于高斯曲线拟合与边缘局部区域效应相结合的亚像素边缘检测方法,获取高精度边缘,提高标志点检测精度;使用基于透视变换图像矫正的标志点快速排序匹配方法,进行相机快速高精度标定。分析投影仪标定时的相位误差,提出了一种基于径向基的线性插值方式,提高标志点圆心相位获取精度。实验验证,使用上述亚像素边缘检测方式,标志点的边缘残差为0.0871,对比基于高斯曲线的拟合方式,精度提高了41%,相机标定重投影误差均值为0.0524像素;使用上述相位插值方式,投影仪标定重投影误差均值为0.1203像素,对比使用双线性插值方式,标定精度提高23.9%。     

结构光测量技术中的投影仪标定算法

详细介绍了投影机模型,并提出一种简单、高精度的投影仪参数标定算法,该算法将投影仪当作一个逆向的相机,使用一块带有圆形标志点的平面标定板对投影仪进行标定.标定过程中,使用两组不同方向的光栅图像建立投影仪图像和相机图像的对应关系,从而得到投影仪标定所需的图像数据,将投影仪标定转化为成熟的相机标定,然后使用相机标定算法对投影仪进行高精度标定.实验结果表明,所提议的投影仪标定算法操作过程简单,标定精度可达0.312 pixel.     

基于相位标靶的投影仪畸变测量与校正

针对传统的投影仪畸变标定方法系统结构和理论推导复杂等问题,提出一种基于相位标靶的投影仪畸变测量和校正方法。该方法以附有全息投影膜的液晶显示屏作为相位标靶,液晶显示屏依次显示水平和垂直方向的正弦条纹图像,投影仪向相位标靶依次投射水平和垂直方向的正弦条纹图像,并分别计算显示条纹和反射条纹的绝对相位。利用两组相位在相机像素上的对应关系,将投影仪投射相位转换到液晶显示屏相位坐标系中,从而测得投影仪的畸变。根据采集的相位空间关系进行畸变校正,使投影仪投射的等相位线在相位标靶上呈直线分布。实验结果证明,该方法可测量并校正投影仪的畸变,不受相机成像质量的影响,可为条纹投影三维形貌测量技术提升投影质量。     

利用预失真条纹校正PMP系统投影仪畸变的研究*

依据摄像机畸变模型提出了一种投影条纹相位畸变校正方法来简化相位-高度映射关系.该方法首先通过投两套互相垂直的相移正弦条纹,以相位值代替投影仪像素坐标,将投影仪当成摄像机看待,标定出投影仪的内参量.然后根据标定出的投影仪镜头畸变参量对理想相位施加反向的畸变,在投影时反向畸变的光栅通过镜头畸变,又成为理想的光栅,从而简化了相位-高度映射关系.实验中,虽然由于测量误差的影响,校正后的投影仪径向畸变系数还是比原来小了1个数量级.     

单摄像机单投影仪结构光三维测量系统标定方法

系统参数的标定是结构光三维测量系统工作的基础,且参数标定的精度直接影响测量的精度,其中投影仪目前还存在标定过程复杂、精度较低等问题。为解决该问题,通过投影一组圆阵图案到一块本身带有特征圆的平板上,并由摄像机拍摄;基于二维射影变换理论,通过误差补偿法建立投影仪图像坐标和摄像机图像坐标的对应关系,利用该对应关系计算获取标定点的投影仪图像坐标;以标定点的两组图像坐标和世界坐标为初始值,使用非线性算法对系统进行全参数整体优化,完成系统的标定。实验验证了系统标定误差最大值小于0.05 mm,误差均方根小于0.03 mm,结果表明该方法标定过程简单,能够有效地提高标定精度,具有较广的适用性。     

利用预失真条纹校正PMP系统投影仪畸变的研究

依据摄像机畸变模型提出了一种投影条纹相位畸变校正方法来简化相位-高度映射关系.该方法首先通过投两套互相垂直的相移正弦条纹,以相位值代替投影仪像素坐标,将投影仪当成摄像机看待,标定出投影仪的内参量.然后根据标定出的投影仪镜头畸变参量对理想相位施加反向的畸变,在投影时反向畸变的光栅通过镜头畸变,又成为理想的光栅,从而简化了相位-高度映射关系.实验中,虽然由于测量误差的影响,校正后的投影仪径向畸变系数还是比原来小了1个数量级.     

基于两个正交一维物体的单幅图像相机标定

提出了一种利用两个正交一维物体构成"T"型靶标进行摄像机标定的新方法。该方法只需对"T"型靶标上已知坐标的5点投影一幅图像,然后根据柔性靶标原理计算出由虚点和标记点组成的共直线的4点,由射影变换同素性、接合性以及交比不变性标定出镜头的一阶径向畸变参数。利用已知畸变参数对图像进行畸变校正,然后由基于两个正交一维物体坐标变换的方法即可标定出相机的内外参数。该方法线性求解镜头畸变参数,避免了传统方法非线性迭代优化过程中产生的参数耦合现象。实验表明,不进行镜头畸变校正则相机标定精度随着图像噪声的增加呈不稳定状态;进行畸变校正后对简单标定计算的初始值进行优化得到稳定的高精度标定结果。整个实验设备简单,操作方便,只需一幅图像即可实现镜头畸变和相机内外参数的标定,可以达到实时的效果。     

基于仿射近似投影模型的长焦相机标定方法

鉴于透视投影模型在长焦相机标定过程中存在过参数化的问题,采用仿射近似投影模型对长焦相机成像过程进行建模,并提出了基于仿射近似投影模型的长焦相机标定方法。首先,深入分析了仿射投影位姿模糊的形成机制,在此基础上详细推导了仿射近似投影下基于平面模板的长焦相机内外参数解算方法;然后,基于透视投影模型,以重投影像点残差平方和最小为目标函数,对内外参数初值进行优化求精;最后,针对仿射投影模型的位姿模糊,在平面标定模板基础上附加微凸圆柱标志。仿真和实际实验结果显示,所提出的长焦相机标定方法有效可行,在实验室环境下重建平面目标的离面中误差优于0.02 mm。     

Accurate calibration for a camera–projector measurement system based on structured light projection

The accurate calibration for a camera–projector measurement system based on structured light projection is important to the system measurement accuracy. This study proposes an improved systematic calibration method focusing on three key factors: calibration model, calibration artifact and calibration procedures. The calibration model better describes the camera and projector imaging process by considering higher to fourth order radial and tangential lens distortion. The calibration artifact provides a sufficient number of accurate 3D reference points uniformly distributed in a common world coordinate system. And the calibration procedures calibrate the camera and projector simultaneously based on the same reference points to eliminate the influences of the camera calibration error on the projector calibration. The experiments demonstrate that our calibration method can improve the measurement accuracy by 47%.     

A novel optimization method of camera parameters used for vision measurement

Camera calibration plays an important role in the field of machine vision applications. During the process of camera calibration, nonlinear optimization technique is crucial to obtain the best performance of camera parameters. Currently, the existing optimization method aims at minimizing the distance error between the detected image point and the calculated back-projected image point, based on 2D image pixels coordinate. However, the vision measurement process is conducted in 3D space while the optimization method generally adopted is carried out in 2D image plane. Moreover, the error criterion with respect to optimization and measurement is different. In other words, the equal pixel distance error in 2D image plane leads to diverse 3D metric distance error at different position before the camera. All the reasons mentioned above will cause accuracy decrease for 3D vision measurement. To solve the problem, a novel optimization method of camera parameters used for vision measurement is proposed. The presented method is devoted to minimizing the metric distance error between the calculated point and the real point in 3D measurement coordinate system. Comparatively, the initial camera parameters acquired through linear calibration are optimized through two different methods: one is the conventional method and the other is the novel method presented by this paper. Also, the calibration accuracy and measurement accuracy of the parameters obtained by the two methods are thoroughly analyzed and the choice of a suitable accuracy evaluation method is discussed. Simulative and real experiments to estimate the performance of the proposed method on test data are reported, and the results show that the proposed 3D optimization method is quite efficient to improve measurement accuracy compared with traditional method. It can meet the practical requirement of high precision in 3D vision metrology engineering.     

激光投影成像式运动目标位姿测量与误差分析

为了实现室内运动目标位姿的高精度测量,建立了一套激光投影成像式位姿测量系统.该系统利用两两共线且交叉排列在同一平面上的点激光投射器作为合作目标捷联在运动目标上,通过与光斑接收幕墙的配合共同组成运动目标位姿测量基线放大系统,利用高速摄像机实时记录幕墙上投影光斑的位置,利用摄像机标定结果求解投影光斑的世界坐标,利用投影光斑之间构成的单位向量建立运动目标位姿解算模型.最后,根据测量原理推导了图像坐标提取、摄像机外部参数标定、光束直线度与目标位姿解算结果之间的误差传递函数.实验结果表明,当摄像机的视场范围为14 000mm×7 000mm时,测量系统的姿态角测量精度为1′(1δ),位置测量精度为5mm,且误差大小与目标位姿测量误差传递函数理论计算值一致,验证了本文提出的目标位姿测量方法与测量误差传递模型的准确性,能够满足目标位姿测量高精度的要求.     

A flexible and rapid micro-adjustment algorithm for structured light 3D measurement system with camera–projector

The structured light 3D measurement system with camera–projector has been widely studied and applied because of its characteristics of simple structure. In practice, we find that slight shock, vibration, or long-term applying may slightly reduce its level of measurement accuracy; thus, correcting the system parameters is occasionally necessary. However, most calibration algorithms are complicated and time-consuming procedures, not suitable for flexible and rapid precise calibration operation. To address this limitation, a flexible and rapid system parameter micro-optimization algorithm based on an implicit projection model is proposed. With a flexible measurement of an arbitrary 3D gauge, the system parameters are optimized rapidly by Levenberg-Marquardt (L-M) algorithm; thus, the high degree of accuracy of the system can be restored. Experiments were performed to validate the availability and reliability of the adjustment method. The algorithm can meet the convenient and real-time accuracy maintenance in practical application for structured light 3D measurement system.     

光学三维扫描仪光强传递函数的测量和校正

由于数字光栅投影仪的光强传递函数对于正弦投影条纹的质量以及相位测量精度起着至关重要的作用,本文提出了一种校正光学三维扫描仪光强传递函数的新方法。首先,分析了由于投影仪非线性响应引起的光栅谐波的相位测量误差;然后,通过投影一组不同灰度级的图像,并利用光功率计测出数字投影仪投出图像的亮度。接着,通过分析得到数字投影仪的非线性响应特性曲线,再经过数据处理,即可获得投影仪的光强传递函数;最后,对光强传递函数进行反函数逆变换,得到一个校正后的非正弦光栅,利用投影仪对该光栅的投影即可在被测物体表面上获得一个正弦光栅。数字投影仪对标准平板的测量结果表明,校正前平均误差为0.71 mm,校正后为0.55 mm;对于标准量块的测量,校正前的平均误差为0.62 mm,校正后为0.15 mm。上述结果表明,本文提出的方法可以减小由于系统非线性响应引起的测量误差并提高测量精度。     

A vision measurement model of laser displacement sensor and its calibration method

Laser displacement sensors (LDSs) use a triangulation measurement model in general. However, the non-linearity of the triangulation measurement model influences the measurement accuracy of the LDS, and the geometric parameters calibration process of the components of the LDS is tedious. In this paper, we present a vision measurement model of the LDS based on the perspective projection principle. Furthermore, a corresponding calibration method is proposed. A planar target with featured lines is moved by a 2D moving platform to some preset known positions. At each position, the world coordinates of calibration points are obtained by the cross ratio invariance principle and the linear array camera of the LDS is used for collecting target images. The simulations verify the effectiveness of the proposed model and the feasibility of the calibration method. The experimental results indicate that the calibration method achieves a calibration accuracy of 0.026 mm. Compared with the traditional measurement model, the vision measurement model of the LDS is more comprehensive and avoids a linear approximation procedure, and the corresponding calibration method is easily complemented.     

Precise full-field distortion rectification and evaluation method for a digital projector

Digital projectors have been widely used in many accuracy-sensitive fields. Although some calibration methods have been proposed to obtain the intrinsic parameters for a digital projector, especially the radial and tangential distortion, there are few studies on how to rectify the projected image to obtain an ideal projection pattern and further evaluate the results. In this paper, a precise full-field image rectification technique is proposed based on the principle of projector calibration. The pixel remapping and interpolation techniques are detailed step by step. All of the method’s steps maintain subpixel accuracy. Moreover, a full-field verification method is presented to evaluate the effectiveness of the projector distortion procedure using a full-field phase map. A full-field non-linear distortion distribution map can be generated to represent distortion characteristics of nearly all the pixels of a projector in a very intuitive way. The experimental results validate and show the effectiveness of the proposed full-field rectification technique and evaluation method.     

结构光三维成像系统的计算机仿真

基于相位测量轮廓术和摄像机模型,提出一种结构照明三维成像系统的高精度计算机仿真算法。对于给定的物体三维模型,首先根据系统结构,采用Z缓冲技术消除遮挡和阴影部分,得到与摄像机像素点对应的物体表面采样点三维坐标,再使用统一的数学模型和方法处理投影过程。根据摄像机及投影仪的内、外参数,最终得到了摄像机像素点、物体表面采样点和投影仪像素坐标三者之间的对应关系,从而实现了结构照明三维成像系统仿真。为实际系统的结构设计、调整和参数校正提供了参考。