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。     

结构光三维测量系统标定的关键算法研究

系统参数标定是结构光三维测量系统的关键问题之一,标定板特征圆圆心检测精度与投影仪、相机镜头gamma效应引起的相位误差是系统参数标定的主要误差来源。采用Sobel算子粗定位标定板特征圆的边缘点,以正交傅里叶-马林矩(OFMM)算子对边缘点进行亚像素定位,用椭圆拟合法确定特征圆圆心的方法提高标定板特征圆检测精度。同时,推导结构光三维测量系统gamma非线性数学模型,将计算得到的系统gamma值的倒数作为投影正弦光栅的指数以降低gamma效应引起的相位误差。实验结果证明了该方法的准确性,与不采用亚像素边缘检测与gamma校正相比,X、Y方向的标定精度分别提高约3.5倍与5倍。     

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.     

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。     

基于立体标靶的双目系统标定研究

条纹投影三维测量技术的检测精度依赖于绝对相位与深度关系的标定过程,传统的标定方法步骤复杂、用时较长,在双目测量系统中对左右相机分别标定时尤为明显。因此设计一种基于立体靶标的标定方法,靶标由两个平面组成,各个靶标平面上附着规格已知的图案,平面连接处用特殊图案标识,用于区分左右两面。立体标靶实现双目测量系统相机外部参数与相位-深度的同时标定,将标定时间减少了一半,简化了标定流程;经过实验验证,利用立体标靶可以精确地进行深度(Z)以及横向(XY)的标定,实测误差小于0.053毫米,方法在双目乃至多节点三维测量系统的标定过程中具有应用价值,增加标定效率同时可避免累计误差产生。     

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。     

基于柔性靶标定位实现图像拼接的多相机三维测量系统

提出一种基于柔性靶标定位实现图像拼接的多相机三维测量系统,采用一个激光投影仪投影大幅条纹,多相机分布式采集的方法扩展视觉三维测量系统的测量范围。标定过程首先使用小型平面靶标标定基准相机二维图像坐标和相位值到三维世界坐标的映射关系,之后在相邻相机部分视场(FOV)重合的前提下,利用柔性靶标定位标定相邻相机图像坐标的转换关系,最后将各个相机的图像坐标全部转化到基准相机的图像坐标系下完成图像拼接,由基准相机图像坐标到世界坐标的映射完成全局三维测量。实验结果表明,使用图像拼接方法的测量精度略低于相机单视场测量的精度,但精度损失较小,满足工业在线测量的要求。该方法避免使用昂贵的辅助测量仪器和加工高精度大型靶标,为多相机视觉测量提供了成本低、使用方便的解决方案。     

超大视场长波红外立体视觉外部参数标定及内外参数评价

在红外光谱中,大气对不同波长辐射透过率不同,透过率较高的波段范围称为大气窗口。为在大视场角范围内探测目标在长波红外光谱的辐射,弥补传统可见光相机在复杂环境下不能探测目标的缺陷,超大视场长波红外相机应运而生。相比于传统可见光相机,超大视场长波红外相机覆盖视场大,能够用于夜间、烟雾等复杂环境,具有一定穿透效果。双目超大视场长波红外立体视觉系统可用于车辆夜间辅助驾驶,军用无人化作战平台全天候信息侦察等领域。作为实现立体视觉的第一步,标定的准确性严重影响立体视觉中物体三维重建精度,因此提高标定准确性是立体视觉研究中的关键问题。标定目的是求出立体视觉成像的内部参数和外部参数,内部参数描述相机镜头成像的物像关系,外部参数表示两个相机之间的相对位置关系。但超大视场长波红外相机成像畸变严重、分辨率低、图像对比度低,对立体视觉标定造成极大困难。为准确标定超大视场长波红外立体视觉外部参数,在Scaramuzza通用相机模型基础上提出了一种基于最小二乘法的外部参数标定方法;为评价内外参数标定结果准确性,以常用单目角点重投影误差评价内部参数为基础,引入外部参数,提出一种双目角点重投影误差评价方法。为验证方法有效性和准确性,使用主动红外辐射标定板生成角点,分别采用视场角(FOV)为180°和210°的两组双目超大视场长波红外相机,在不同位置上进行标定实验。实验结果显示,常用的Bouguet方法双目平均重投影误差(BMRE)在0.782～0.943 pixels,而基于最小二乘法方法BMRE处于0.620～0.754 pixels,实验数据表明该方法有效降低了双目角点重投影误差,提高了外部参数标定准确性。此外,评价方法操作简便、客观准确,避免在评价过程中对物点三维重建从而引入额外误差,并且不需要高精度三维坐标测量设备。     

相机内参量及像差系数与外参量的解耦标定方法

基于无穷远点与相机内参量关系,提出了一种相机内参量及像差系数与外参量解耦标定方法.首先,根据平面单应计算绝对二次曲线在像面的投影方程,线性求解相机内参量;然后,将重投影像点视为理想像点线性求解像差系数,并计算像点重投影误差;最后,将序列图像的平面单应作为待优化参量,以最小化像点重投影误差为目标函数,重复上述过程,输出最优的相机内参量和像差系数.在相同配置下,分别对本文方法和张正友平面靶板标定方法的标定准确度进行仿真与对比分析.基于不同姿态和位置的27幅棋盘格图片,分别利用这两种方法对相机内参量进行标定实验.实验结果表明:与张正友平面靶板标定方法相比,本文方法的标定准确度提高了至少1％;在实物实验中,张正友平面靶板标定方法和本文方法的重投影残差分别为0.064像素和0.008像素.     

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。     

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.     

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.     

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。