基于单幅图片的相机完全标定

现有相机标定方法的标定过程比较繁琐,不利于标定相机的广泛使用。为此,从摄像机镜头畸变矫正着手,结合标定板信息及消失点约束,提出一种基于单张图片的相机标定方法。利用非线性迭代得到相机镜头的畸变系数,通过线性求解得出相机的内参,直接计算得到相机的外参,从而实现仅需拍摄单张标定板图片的相机完全标定。实验结果表明,该方法在标定板与视平面夹角小于45°的情况下均能成功标定,并且重投影误差小于0.3像素。     

基于数据拟合的摄像机标定和图像的数值校正

采用的摄像机成像模型考虑了透镜的径向畸变和切向畸变。标定过程包括对摄像机的内外部参数的直接线性变换估算和基于内部映射牛顿法的子空间置信域法的非线性优化算法优化。同时提出了对畸变图像校正的数值计算方法。     

用于交会测量的摄像机标定系统设计

介绍了一种简易的摄像机立体标定系统的设计方案,主要应用于多CCD交会测量技术中,可以完成单个摄像机的标定、多个摄像机之间的立体标定和标定精度评估等功能.建立了包含透镜径向畸变和切向畸变的摄像机成像模型,采用两步法求解摄像机参数,最后通过交会测量得到的多个棋盘格的边长与实际边长的误差量来衡量摄像机标定的精度.该系统不要求使用者具有专业的3D几何知识,速度快,成本低,而且可以达到很高的精度.     

A variational approach to problems in calibration of multiple cameras

This paper addresses the problem of calibrating camera parameters using variational methods. One problem addressed is the severe lens distortion in low-cost cameras. For many computer vision algorithms aiming at reconstructing reliable representations of 3D scenes, the camera distortion effects will lead to inaccurate 3D reconstructions and geometrical measurements if not accounted for. A second problem is the color calibration problem caused by variations in camera responses that result in different color measurements and affects the algorithms that depend on these measurements. We also address the extrinsic camera calibration that estimates relative poses and orientations of multiple cameras in the system and the intrinsic camera calibration that estimates focal lengths and the skew parameters of the cameras. To address these calibration problems, we present multiview stereo techniques based on variational methods that utilize partial and ordinary differential equations. Our approach can also be considered as a coordinated refinement of camera calibration parameters. To reduce computational complexity of such algorithms, we utilize prior knowledge on the calibration object, making a piecewise smooth surface assumption, and evolve the pose, orientation, and scale parameters of such a 3D model object without requiring a 2D feature extraction from camera views. We derive the evolution equations for the distortion coefficients, the color calibration parameters, the extrinsic and intrinsic parameters of the cameras, and present experimental results.     

Self-calibration of wireless cameras with restricted degrees of freedom

This paper presents an approach for the automatic calibration of low-cost cameras which are assumed to be restricted in their freedom of movement to either pan or tilt movements. Camera parameters, including focal length, principal point, lens distortion parameter and the angle and axis of rotation, can be recovered from a minimum set of two images of the camera, provided that the axis of rotation between the two images goes through the camera’s optical center and is parallel to either the vertical (panning) or horizontal (tilting) axis of the image. Previous methods for auto-calibration of cameras based on pure rotations fail to work in these two degenerate cases. In addition, our approach includes a modified RANdom SAmple Consensus (RANSAC) algorithm, as well as improved integration of the radial distortion coefficient in the computation of inter-image homographies. We show that these modifications are able to increase the overall efficiency, reliability and accuracy of the homography computation and calibration procedure using both synthetic and real image sequences.     

Pan–tilt–zoom camera calibration and high-resolution mosaic generation

In this paper, we discuss the problem of estimating parameters of a calibration model for active pan–tilt–zoom cameras. The variation of the intrinsic parameters of each camera over its full range of zoom settings is estimated through a two step procedure. We first determine the intrinsic parameters at the camera’s lowest zoom setting very accurately by capturing an extended panorama. The camera intrinsics and radial distortion parameters are then determined at discrete steps in a monotonically increasing zoom sequence that spans the full zoom range of the camera. Our model incorporates the variation of radial distortion with camera zoom. Both calibration phases are fully automatic and do not assume any knowledge of the scene structure. High-resolution calibrated panoramic mosaics are also computed during this process. These fully calibrated panoramas are represented as multi-resolution pyramids of cube-maps. We describe a hierarchical approach for building multiple levels of detail in panoramas, by aligning hundreds of images captured within a 1–12× zoom range. Results are shown from datasets captured from two types of pan–tilt–zoom cameras placed in an uncontrolled outdoor environment. The estimated camera intrinsics model along with the cube-maps provides a calibration reference for images captured on the fly by the active pan–tilt–zoom camera under operation making our approach promising for active camera network calibration.     

一种摄像机成像误差的模型化修正方法

本文针对摄像机成像误差问题,首先提出了一种新 的径向畸变模型,利用此模型推出了能精确标定摄像机的关键参数（有效焦距、平移矢量的 Z向分量以及径向畸变系数）的线性算法;同时提出了一种成像系统误差的修正模型,并利 用系统辨识方法正确估计了该模型的各参数;并进行了实验验证.这项研究必将使得摄像机 成像的误差整体降低,从而提高了测量精度.     

双线阵CCD相机的畸变校正和标定方法

在双线阵CCD的三维重建中,对线阵CCD相机的标定和镜头畸变校正是基础环节。提出了一种用于三维重建中的双线阵CCD标定及镜头畸变校正方法。根据左右相机间的单应性关系,以及线阵CCD的成像原理,将双目相机间的空间关系分解成姿态角与错切角的关系。通过靶图数据的拟合,对姿态角和镜头畸变进行校正,根据求出的错切角完成相机间的标定,实现对具有镜头畸变的双线阵CCD的标定。实验结果表明,标定和校正精度满足后续三维重建中图像匹配的需求。     

一种基于非量测畸变校正的摄像机标定方法

设计一种基于非量测畸变校正的摄像机标定方法.该方法利用单参数除式模型校正镜头畸变,根据直线透视投影保留同素性,通过拉凡格氏法（LM）优化标定出畸变模型系数和摄像机主点坐标,然后校正成像点,使其满足针孔模型映射关系.根据内参数的两个基本方程,线性求解剩余参数.实验表明,该方法在非量测标定过程具有较好的鲁棒性,且对比张正友标定方法,可在单幅标靶图像下进行标定,避免了模型内外参数耦合在一起,提高了标定效率.     

Some aspects of zoom lens camera calibration

Zoom lens camera calibration is an important and difficult problem for two reasons at least. First, the intrinsic parameters of such a camera change over time, it is difficult to calibrate them on-line. Secondly, the pin-hole model for single lens system can not be applied directly to a zoom lens system. In this paper, we address some aspects of this problem, such as determining principal point by zooming, modeling and calibration of lens distortion and focal length, as well as some practical aspects. Experimental results on calibrating cameras with computer controlled zoom, focus and aperture are presented     

基于畸变校正的双目立体摄像机线性标定

利用透视变换原理建立双目立体摄像机数学模型,全面考虑了镜头的径向畸变和切向畸 变,提出一种线性求解摄像机参数的标定方法,改变了以往的摄像机标定依赖于非线性优化的缺点,避免了非线性优化的不稳定性.该标定方法在单摄像机模型的基础上,加入对双摄像机相对位置的确定,通过成像过程中坐标系之间的转换,较好地实现了双目立体摄像测量系...     

Image-based lens geometric distortion correction using minimization of average bicoherence index

In this paper, a lens geometric distortion correction method for low-cost digital cameras is described. The lens distortion coefficient is estimated by the value minimizing average bicoherence index which denotes image-dependent higher-order correlations in the frequency domain. In order to formulate the minimization of the average bicoherence index in terms of the lens distortion coefficient alone, the feasibility of a square-pixel assumption and the effect of the image center bias on the image quality are shown experimentally. At the same time, a computationally efficient method for calculating the bicoherence index is proposed, which comprises an approximation of coordinate resampling and development of a relationship between the lens distortion coefficients of the original and its reduced image. Depending on the spatial distribution of image features, the performance of the proposed method can be made comparable to that of precision camera calibration.     

基于空间透视不变量的摄象机标定方法

本文给出了一种以空间不变量的数据来计算摄象机外部参数的方法．空间透视不变量是指在几何变换中如投影或改变观察点时保持不变的形状描述．由于它可以得到一个相对于外界来讲独立的物体景物的特征描述，故可以很广泛的应用到计算机视觉等方面．摄象机标定是确定摄象机摄取的２Ｄ图象信息及其３Ｄ实际景物的信息之间的变换关系，它包括内部参数和外部参数两个部分．内部参数表征的是摄象机的内部特征和光学特征参数，包括图象中心（Ｃｘ，Ｃｙ）坐标、图象尺度因子Ｓｘ、有效的焦距长度ｆ和透镜的畸变失真系数Ｋ；外部参数表示的是摄象机的位置和方向在世界坐标中的坐标参数，它包括平移矩阵Ｔ和旋转矩阵Ｒ３×３，一般情况下可以写成一个扩展矩阵［ＲＴ］３×４．本文基于空间透视不变量的计算数据，给出了一种标定摄象机外部参数的方法，实验结果表明该方法具有很强的鲁棒性．     

Robust metric calibration of non-linear camera lens distortion

Camera lens distortion is crucial to obtain the best performance cameral model. Up to now, different techniques exist, which try to minimize the calibration error using different lens distortion models or computing them in different ways. Some compute lens distortion camera parameters in the camera calibration process together with the intrinsic and extrinsic ones. Others isolate the lens distortion calibration without using any template and basing the calibration on the deformation in the image of some features of the objects in the scene, like straight lines or circles. These lens distortion techniques which do not use any calibration template can be unstable if a complete camera lens distortion model is computed. They are named non-metric calibration or self-calibration methods.Traditionally a camera has been always best calibrated if metric calibration is done instead of self-calibration. This paper proposes a metric calibration technique which computes the camera lens distortion isolated from the camera calibration process under stable conditions, independently of the computed lens distortion model or the number of parameters. To make it easier to resolve, this metric technique uses the same calibration template that will be used afterwards for the calibration process. Therefore, the best performance of the camera lens distortion calibration process is achieved, which is transferred directly to the camera calibration process.     

基于OpenCV的摄像机标定

以增强现实系统中摄像机标定技术为研究对象,分析了开放计算机视觉函数库OpenCV中的摄像机模型,特别充分考虑了透镜的径向畸变和切向畸变影响及求解方法,给出了基于OpenCV的摄像机标定算法.该算法充分发挥了OpenCV的函数库功能,提高了标定精度和计算效率,具有良好的跨平台移植性,可以满足增强现实和其它计算机视觉系统的需要.     

一种基于斜率的摄像机畸变校正方法

普通 CCD摄像机在成像时都存在畸变成像误差 ,在机器人视觉检测及自动装配中 ,有效地进行误差校正对准确确定物体的位置具有重要的意义 .本文采用带有一阶径向畸变的小孔摄像机模型 ,提出一种基于线段斜率的方法 ,对摄像机镜头的径向畸变进行校正 ,不必标定太多的摄像机的外参数 ,方法简洁 ,适合于视觉系统中对摄像机畸变的实时校正 ,或对摄像机捕获的图像进行几何校正 .实验表明 ,具有很强的鲁棒性和较高的校正精度     

Automatic Georeferencing of Images Acquired by UAV’s

This paper implements and evaluates experimentally a procedure for automatically georeferencing images acquired by unmanned aerial vehicles (UAV’s) in the sense that ground control points (GCP) are not necessary. Since the camera model is necessary for georeferencing, this paper also proposes a completely automatic procedure for collecting corner pixels in the model plane image to solve the camera calibration problem, i.e., to estimate the camera and the lens distortion parameters. The performance of the complete georeferencing system is evaluated with real flight data obtained by a typical UAV.     

试飞测试中摄像机标定方法研究

随着数码相机技术和摄影测量技术的发展,越来越多的数字摄像机应用于试飞测试中,而摄像机标定是其成功应用于飞行试验的关键之一。为了突破试飞测试中现有的仅以点特征作为控制,充分利用现有设备条件,更好地解决加装在飞机上的摄像机在飞行过程中的实时标定问题,采取内标定与实时外标定两步实现摄像机标定的方法。着重探讨了一种基于平行直线的摄像机内标定方法,详细论述了基于灭点约束和直线几何约束的摄像机标定解算模型,该方法在无控制点的情况下可得到每个摄像机的内方位元素、各项畸变改正系数和外方位角元素;并简要介绍了基于单片后方交会的实时外标定方法。实际数据的试验结果表明,该方法切实可行,能够获得精确、稳定的参数结果,有效减少了摄像机标定过程中所需布设的控制点数,从而提高了试飞测试中精确测量导弹运动轨迹、机翼变形测量等工作的可实施性。     

Self-calibration of hybrid central catadioptric and perspective cameras

Hybrid central catadioptric and perspective cameras are desired in practice, because the hybrid camera system can capture large field of view as well as high-resolution images. However, the calibration of the system is challenging due to heavy distortions in catadioptric cameras. In addition, previous calibration methods are only suitable for the camera system consisting of perspective cameras and catadioptric cameras with only parabolic mirrors, in which priors about the intrinsic parameters of perspective cameras are required. In this work, we provide a new approach to handle the problems. We show that if the hybrid camera system consists of at least two central catadioptric and one perspective cameras, both the intrinsic and extrinsic parameters of the system can be calibrated linearly without priors about intrinsic parameters of the perspective cameras, and the supported central catadioptric cameras of our method can be more generic. In this work, an approximated polynomial model is derived and used for rectification of catadioptric image. Firstly, with the epipolar geometry between the perspective and rectified catadioptric images, the distortion parameters of the polynomial model can be estimated linearly. Then a new method is proposed to estimate the intrinsic parameters of a central catadioptric camera with the parameters in the polynomial model, and hence the catadioptric cameras can be calibrated. Finally, a linear self-calibration method for the hybrid system is given with the calibrated catadioptric cameras. The main advantage of our method is that it cannot only calibrate both the intrinsic and extrinsic parameters of the hybrid camera system, but also simplify a traditional nonlinear self-calibration of perspective cameras to a linear process. Experiments show that our proposed method is robust and reliable.     

线阵相机的圆环旋转标定方法

由于传统线阵相机的标定过程复杂,且对标定物精度要求较高,难以保证缺陷的定位精度,本文提出一种线阵相机的圆环旋转标定方法以提高缺陷的定位精度。该方法设计一种新型的圆环形标定板,在静态标定基础上通过旋转线阵相机采集相机视线与圆的交点的坐标,得到旋转角度以及多组标定点,建立线阵相机的成像模型和径向畸变模型,通过非线性优化整体误差函数求解相机的内参和畸变参数,同时分析相机不同旋转角度对标定精度的影响。实验结果表明,当θ≤20°时,该方法的标定精度在0.35 pixel以内,满足实际检测的定位要求,并且在PCB缺陷检测中得到较好的验证。