大视场短焦距镜头CCD摄像系统的畸变校正

从光学测量角度出发,结合计算机视觉中的摄像机标定方法,解决了大视场短焦距镜头CCD摄像系统的畸变校正问题。与摄像机标定不同,畸变校正中仅标定内部参数,外部参数作为已知条件。采用线性畸变模型,由最小二乘法解线性方程组得到摄像系统畸变模型的畸变系数。介绍了数字图像中像素间距和光学中心的标定方法。通过比较由标定参数得到的畸变图像和摄像机采集的畸变图像对实验标定精度进行评定,实验结果表明边缘视场(112°)的标定精度达到了0 75%。     

Accuracy evaluation of optical distortion calibration by digital image correlation

Due to its convenience of operation, the camera calibration algorithm, which is based on the plane template, is widely used in image measurement, computer vision and other fields. How to select a suitable distortion model is always a problem to be solved. Therefore, there is an urgent need for an experimental evaluation of the accuracy of camera distortion calibrations. This paper presents an experimental method for evaluating camera distortion calibration accuracy, which is easy to implement, has high precision, and is suitable for a variety of commonly used lens. First, we use the digital image correlation method to calculate the in-plane rigid body displacement field of an image displayed on a liquid crystal display before and after translation, as captured with a camera. Next, we use a calibration board to calibrate the camera to obtain calibration parameters which are used to correct calculation points of the image before and after deformation. The displacement field before and after correction is compared to analyze the distortion calibration results. Experiments were carried out to evaluate the performance of two commonly used industrial camera lenses for four commonly used distortion models.     

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%.     

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。     

A calibration method of lens distortion for line scan cameras

We present a practical method to calibrate the lens distortion in line scan cameras. The distortion correction software based on this method has been designed and implemented in the digital protection of cultural relics. In this paper, a lens distortion model which applies to line scan cameras is derived from the widely used array camera distortion model. Then, a new calibration method which utilizes the imaging characteristic of equidistant collinear feature points is proposed to calibrate the model. Experiment results show the proposed calibration method is stable and effective.     

Correcting non-linear lens distortion in cameras without using a model

Camera lens distortion calibration is the first step in resolving any metric application with a camera. To date, lens distortion was corrected using some existing lens distortion non-metric or self-calibration methods. Using a lens distortion model means defining a global rule to correct the entire image. This global rule does not take into account particular lens distortion effects not represented by the model. Moreover, to calibrate the model, only some features of the scene such as straight lines, circles or vanishing points are used. Since only the feature of the scene used to calibrate the model is guaranteed by the distortion rectification, it is certain that the model will not be precise. The result is an approximation of the real image distortion.To improve the lens distortion rectification, a method without using a model is proposed. Using a set of control points distributed across the entire image, they are corrected to assure all the restrictions of the scene. With both sets of points, the points detected in the image and the undistorted ones, image local transformations are defined considering only nearby control points. Rather than calibrating a global model, local functions are characterized. The distortion correction is defined by a rectification surface composed of local surface patches each influenced by nearby control points. This method is more sensitive to local deformations and allows the image to be corrected in accordance with its distortion.     

Calibration and correction of lens distortion for two-dimensional digital speckle correlation measurement

Lens distortion practically presents in optical imaging system using in two-dimensional digital speckle correlation measurement (2D-DSCM) system, and gives rise to additional errors in the displacement and strain measurement. Camera calibration procedure is performed to obtain the coefficients of radial distortion and tangential distortion. The corrected displacement fields can be calculated using the distortion coefficient. The influence of distortion on displacement and strain measurement errors in experiment is further discussed. The three-point bending test result shows that the camera lens calibration method can effectively eliminate the effect of lens distortion and improve displacement and strain measurement accuracy.     

Using the camera pin-hole model restrictions to calibrate the lens distortion model

Camera calibration required the computation of camera pin-hole and lens distortion models. The lens distortion is estimated alone or together with the pin-hole model, by using some existing lens distortion non-metric or self-calibration methods. If both models are computed together, then the models are adjusted to training data, but not to real camera. This is because both pin-hole and lens distortion models are coupled. If they are computed separately, difficulties arise since calibration of lens distortion alone is an unstable process. To improve existing camera calibration methods, this paper proposes a metric calibration method to compute lens distortion separately from the pin-hole model. This method is solved under stable conditions, independently of the computed lens distortion model, since pin-hole and distortion models are computed separately. Images of a planar template are used. First, using distorted control points extracted from images, a set of undistorted points which fits in the pin-hole model are computed. Second, with distorted and undistorted control points, lens distortion is calibrated by using a metric calibration process.     

采用广角数码相机测量图像显示系统的几何畸变

准确地测量含有广角耦合物镜的图像显示系统的几何畸变是实现图像显示系统几何畸变数字校正的前提和关键。提出了一种以非量测广角数码相机为测量设备的几何畸变的测量方法，首先给出了广角数码相机镜头畸变的标定方法，确定了数码相机镜头畸变系数，然后讨论了基于广角数码相机和Photoshop软件进行图像显示系统几何畸变测量的测量方法，分析了影响测量精度的因素。最后，将本文的测量结果与基于点物成像原理，采用单轴转台和普通数码相机进行测量的测量结果进行了对比，二者吻合得较好。从测量结果看，本文给出的测量方法，其测量精度可以满足工程要求，简单、易行。     

High precision camera calibration in vision measurement

In order to ensure the measurement precision for shape recovery from a stereo vision system, a novel high precision calibration method is presented. Some standard points acquired from the object of interest are used as standard world points. There are four rotation matrices and translation matrices that need to be calibrated, the first is between the left camera and the world coordinate, the second is between the right camera and the world coordinate, the third is between the left camera and the right camera, and the last is between the right camera and the left camera. The lens distortion parameters include radial and tangential distortion. The merits of the calibration method are its high precision, easy of operation, and high reliability.     

一种微小型导引头视场下偏角的标定方法

描述了一种应用于微小型光学导引头视场下偏角标定的方法，通过获得导引头绕自身回转轴线转动时拍摄的固定靶标图像计算不同旋转角度时导引头中心视线落点和摄像机坐标系原点在世界坐标系下的坐标，以拟合获得的这2组点的分布建立空间几何关系进而得出下偏角。给出了3组实验数据，分别检验该方法的标定误差、实际所需的采样点数并给出了实际工作中的应用效果。实验表明该方法可以快速标定导引头系统的下偏角，其标定绝对误差小于0.10°。     

基于天文观测的相机标定及姿态测量技术研究

为利用相机进行天文观测以实现高精度的相机姿态测量,必须先对相机参数进行精确标定。针对传统相机标定方法工作距离有限的问题,提出了以恒星为控制点的相机标定方法,根据球面天文学方法计算观测时刻控制点的世界坐标,利用摄像测量原理建立了恒星观测模型,求解相机的内外参数并分析了误差因素。实验结果表明,该标定方法在不依赖于精密、复杂的外部设备情况下可达到较高精度,并具有较强的抗噪声能力。将标定结果用于天文观测并求解相机姿态,航向角和俯仰角的解算重复性优于10″,能够满足高精度姿态测量的需求。该方法可进一步推广应用于星敏感器的标定。     

超宽视场离轴光学系统畸变一致性校正技术

为满足海岸带超宽视场和高分辨率的动态监测需求,高分辨率宽覆盖已成为空间光学遥感器的重要发展趋势。HY-1C/D卫星海岸带成像仪采用两台相机组合的方式实现大幅宽,单台相机是32°超宽视场离轴光学系统,相机存在弧形畸变且畸变较大。研究了超大视场离轴光学系统畸变一致性校正技术,提出“多变量仿真-高精密测量-交互迭代”的装调方法,开展了兼顾像质、视轴、畸变的多变量全链路仿真计算,通过高精度畸变测量系统实现了畸变补偿的交互迭代调整,解决了镜头装调阶段畸变不可控的难题,实现双台相机畸变一致性控制精度优于0.1%,完全满足测试技术要求,结果表明方法合理可行。     

摄像机标定技术在活塞视觉检测与分选中的应用研究

在机器人视觉检测及自动化分捡中,准确地校正摄像机镜头畸变对获取物体精确图像及确定物体准确位置具有重要意义。采用了带有径向畸变的小孔摄像机模型及基于线段斜率的标定方法。在标定过程中,应用线性算法求解出了镜头的径向畸变系数。实验表明,采用的标定方法简捷有效,其标定结果能够满足研究需要。     

基于共面条件的摄像机非线性畸变自校正

由于制造和装配误差难以完全消除,导致摄像机的光学系统存在不同程度的非线性光学畸变现象。为此,利用不同视角采集图像上同名像点共面的基本原理,推导包含非线性畸变模型的共面条件方程,并采用最小二乘解的广义逆法求解非线性畸变参数,确保摄像机的自校正精度;因无需加工和维护成本很高的精密标定板,也不用制作高精度摄像机运动平台,仅通过自由拍摄方式就能够从多视角获得含6个以上编码点的图像,即可获得摄像系统的非线性畸变参数。因此,较传统的摄像机畸变校正方法而言,自校正过程简单快捷,成本低,多个实例证明技术的正确性与实用性。     

一种成像测量图像径向几何畸变的校正方法

通过对具有径向畸变的摄像机模型的分析,设计了一套求解图像径向几何畸变中心和畸变多项式系数的方案。首先,依据校正样板曲线的弯曲程度应用一元线性回归法和逐次逼近法求取光学图像的几何畸变中心,然后应用递推最小二乘法求解径向几何畸变的多项式系数,最后根据所得到的畸变中心和畸变多项式系数对图像进行校正得到满足要求的图像。仿真试验证明:该方法可以通过一次采集单幅图像对成像系统进行高精度标定,能够对成像测量系统的径向几何畸变进行一定精度的校正。实践证明:该方法通过图像处理的方法提高成像测量系统的精度,降低了系统的设计成本,可以作为成像测量系统中单独标定摄像机畸变参数的一种简单有效的方法。     

A novel planar calibration method using the iterative correction of control points information

In the camera calibration using translational planar object instead of 3D target, the skew affected by the imprecision in installation causes the object to deviate from the designated position, which produces errors to the world coordinates of control points and reduces the calibration accuracy. In this paper, a skew correction model is established to correct this skew. We note and prove that the skew bias of control point which is close to the fix point is tiny. According to the projection regulation, the pixel distance between two adjacent control points which is close to the fix point in skewed situation is a value extremely approximate to that in the ideal situation. Based on this property, we utilize the pixel distance to assign the image coordinates based on the fix point. The assigned values are then employed to estimate the skew factors, by which the initial camera parameters are optimized and lens distortion in the calibration images are corrected. This process is then repeated until convergence. Experiments based on real images prove that this method is more accurate than other methods without correcting skew. The parameters obtained by our method can be applied to the 3D reconstruction directly and effectively.     

机载摄像机快速标定技术研究

针对飞行试验机载摄像机的标定,提出了一种基于光束法平差的高精度像机标定方法。首先,通过在测试目标周围放置带有编码标志点的标定板,拍摄其多种状态,经图像处理,获取标志点的编码以及中心坐标。然后通过相对定向、绝对定向、三维重建、捆绑调整,以及加入标志点之间的距离约束,得到数字摄像机内外方位元素和镜头畸变差参数,实现机载摄像机快速标定。实验结果表明：该标定方法不需要做高精度的现场控制点,重投影误差小于1cm,标定精度满足飞行试验测试要求。     

大尺寸视觉测量系统在线标定的新方法

提出了一种新的基于视场边缘距离相对约束条件的摄像机标定方法,并用于大尺寸测量中摄像机的标定,该方法在标定摄像机内外方位参数的同时也完成了成像畸变的校正,将标定结果用于测量,在4×4×1m3的测量视场内,其相对精度达到1/2000,与传统标定方法相比,该标定方法灵活性高,更加适用于测量视场较大的情况。     

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。