一种不断重定位圆心的鱼眼图像校正方法

针对鱼眼图像传统经度坐标校正效果不明显,提出了一种新的鱼眼图像2D校正算法,通过对每一条畸变的经线,不断重定位圆心位置,重新计算经线上点的坐标,有效地校正桶形畸变.该算法不用进行鱼眼镜头的标定以及参数的估计,也不用寻找三维空间点信息以及在各种坐标系之间进行转换.通过与传统校正算法进行对比,发现本算法能高效快捷地对鱼眼图像进行校正,而且具有较好的效果.     

一种改进的单目机器人立体视觉系统校正方法

基于三棱镜的单目立体视觉系统具有高集成度、低功耗、易装配等特点,但外置的棱镜也会引发不规则的图像畸变,影响成像质量。首先采用双边滤波函数对目标图像进行降噪处理,增强图像中的边界,有效提高标定图像中的特征点提取的准确性;然后结合透视投影中的直线性、交比一致性和没影点收敛性等投影不变性提出一种改进的自适应畸变校正算法。该算法无需畸变模型及畸变参数,通过校正前后特征点的偏移,最终得到畸变校正所需的像素位移图。实验对比了多组图像的特征提取效果和畸变校正结果,并比较了不同校正方法对于系统中产生的不规则畸变的校正效果,结果表明该算法具有鲁棒性和准确性,提高了机器人视觉系统的准确度。     

一种简单而精确的径向畸变标定方法

为了用普通低成本的广角镜头摄像机实现较大视场的精确定量的图像测量，必须对畸变图像进行校正。提出了一种简单而精确的径向畸变标定方法，该方法使用栅格阵列标定模板。首先根据畸变图像中特征点之间的相互位置关系构造出理想图像中的特征点位置；然后以不同的畸变中心假设，计算畸变和理想特征点的矢径坐标，并通过解线性方程组或多项式拟合求出它们之间的函数关系；最后取矢径均方误差最小的参数组作为标定结果。该法可同时获得畸变变换和矫正变换的参数。文中还推导了畸变变换多项式系数与校正图像分辨率之间的反幂比例关系，讨论了畸变函数的阶对校正结果的影响，实验结果表明，取4阶或5阶多项式拟合的结果较好。     

基于等间距线的几何畸变校正

摄像机视觉测量系统中图像存在几何畸变,会降低尺寸测量精度,必须进行校正.目前基于单张图像的畸变校正方法主要有标定板特征点转移矩阵的非参数化方法和利用特征点共线性或无穷点约束条件的参数化方法,由于上述方法需要获取多个特征点的坐标,而获取孤立的坐标点容易造成误差,使得校正效果不好.提出采用等间距线方法,利用畸变模型建立间距...     

基于线性特征的鱼眼图像校正方法

针对鱼眼镜头采集的畸变图像,在棋盘格标定模板的基础上,提出一种有效的校正方法。该方法采用标准畸变模型,首先基于畸变图像的线性特征提出目标函数;然后利用SUSAN改进算法精确定位棋盘格角点坐标;对已得到的有限角点坐标进行畸变曲线拟合,在畸变曲线上提取所需数量的点;最后用渐近寻优算法计算最优畸变系数,使得目标函数最小。实验结果表明,该方法角点定位精确、算法时间复杂度低,能够有效校正鱼眼镜头造成的图像畸变。     

双目视觉的立体标定方法

为实现双目视觉系统的立体标定,分析了摄像机成像模型,并充分考虑了透镜的径向畸变和切向畸变,提出了一种新的立体标定算法。该算法利用张正友的灵活标定算法,初步求取摄像机的内参数,结合Brown算法并提取图像中角点的子像素级坐标,精确求取摄像机内参数和畸变向量。为方便后续的图像校正,基于前面的单个摄像机标定,通过计算空间中的景物点在左右摄像机成像平面上的位置关系,计算出双目视觉系统中两个摄像机之间的旋转矩阵R和平移向量T,从而实现了立体标定。实验结果表明,该算法能取得较高的精度,可以应用于双目视觉系统。     

基于双目视觉的物体尺寸测量系统

提出了一种基于双目视觉的物体尺寸测量系统,用于非接触式测量物体尺寸。该系统采用张正友棋盘标定法进行双目相机标定,并利用标定参数对采集的图像进行校正。通过采用图像分割技术和角点检测算法获取待测物体的特征点。通过立体匹配算法对校正图像进行处理,得到视差图。根据三角形相似性原理计算特征点的三维坐标,计算出物体尺寸的信息。实验结果表明,该系统具备较高的测量精度,具有一定的实用性和应用前景。     

基于灭点的倾斜畸变车牌图像快速校正方法研究

由于相机与汽车牌照之间的方位关系导致了拍摄图像发生倾斜畸变,极大影响了车牌识别率。针对这一问题,利用畸变图像所蕴涵的灭点信息,提出了一种快速校正方法：首先对图像进行预处理,提取车牌的四条边框来产生灭点;然后根据灭点信息快速标定相机内参数并计算空间平面重建矩阵;最后进行空间坐标变换和灰度插值完成畸变图像的校正。实验表明,该方法对于倾斜畸变车牌有良好的校正效果,并有效提高了识别率。     

双目图像校正VLSI硬件电路结构设计

针对已有立体视觉中双目图像校正算法计算复杂度较高,不适合硬件实现的问题,提出了一种双目图像几何校正模型,并设计了VLSI硬件电路结构。利用网格模板标定法获取畸变校正模型参数,进行单目畸变图像的校正;再借助双目标定算法获得双目图像校正外部参数,得到立体校正模型,进行立体校正。结合畸变校正模型和立体校正模型,设计一个新的双目图像几何校正模型,并基于此模型设计双目图像几何校正VLSI硬件电路结构,具有较好的几何校正效果,也能够保证校正后的双目图像分辨率。     

考虑径向畸变的机器人视觉系统的参数标定

针对GRB-400机器人视觉系统,建立完整的摄像机一阶径向畸变模型。用GRB系统的Matrox图像采集卡采集标定点坐标,利用径向排列约束方法 (简称RAC)建立线性方程组求解摄像机的径向畸变参数。基于此畸变参数实现图像校正,以提高对目标物体的定位精度,从而提高机器人视觉系统对摄像机标定参数变化的鲁棒性。实验结果表明,该方法有较高的标定精度。     

Simple calibration algorithm for high-distortion lens camera

A simple and useful calibration method for a TV camera with a high-distortion lens is presented. The parameters to be calibrated are effective focal length, one-pixel width on an image plane, image distortion center, and distortion coefficient. A simple-pattern calibration chart composed of parallel straight lines is introduced as a reference for calibration. An ordinary 2D model fitting is decomposed into two 1D model fittings on the column and row of a frame buffer across the image distortion center by ingeniously utilizing the point symmetry characteristic of image distortion. Some parameters with a calibration chart are eliminated by setting up a calibration chart precisely and by utilizing negligibly low distortion near the image distortion center. Thus, the number of unknown parameters to be calibrated is drastically decreased, enabling simple and useful calibration. The effectiveness of the proposed calibration method is confirmed by experimentation     

Whitt点目标极化定标算法的实验研究

将Whitt等人提出的通用的点目标极化定标算法应用到SIR-C系统获取的L波段多极化数据中,进行定标实验。利用所获取的SIR-C合成孔径雷达图像中存在的点目标,将它们经过SIR-C定标组定标的极化数据作为理论值看待,运用Whitt算法来定标整幅没有定标的图像。最后将实验获取的结果与SIR-C定标组定标结果互相比较,可以看出这个算法具有良好的性能。     

Generalized Camera Calibration Including Fish-Eye Lenses

A method is described for accurately calibrating cameras including radial lens distortion, by using known points such as those measured from a calibration fixture. Both the intrinsic and extrinsic parameters are calibrated in a single least-squares adjustment, but provision is made for including old values of the intrinsic parameters in the adjustment. The distortion terms are relative to the optical axis, which is included in the model so that it does not have to be orthogonal to the image sensor plane. These distortion terms represent corrections to the basic lens model, which is a generalization that includes the perspective projection and the ideal fish-eye lens as special cases. The position of the entrance pupil point as a function of off-axis angle also is included in the model. (The complete camera model including all of these effects often is called CAHVORE.) A way of adding decentering distortion also is described. A priori standard deviations can be used to apply weight to given initial approximations (which can be zero) for the distortion terms, for the difference between the optical axis and the perpendicular to the sensor plane, and for the terms representing movement of the entrance pupil, so that the solution for these is well determined when there is insufficient information in the calibration data. For the other parameters, initial approximations needed for the nonlinear least-squares adjustment are obtained in a simple manner from the calibration data and other known information. (Weight can be given to these also, if desired.) Outliers among the calibration points that disagree excessively with the other data are removed by means of automatic editing based on analysis of the residuals. The use of the camera model also is described, including partial derivatives for propagating both from object space to image space and vice versa. These methods were used to calibrate the cameras on the Mars Exploration Rovers.     

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.     

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。     

一种简单的基于共面的摄像机参数标定方法

共面摄像机标定就是采用平面式模板来确定摄像机内外参数的过程,在此过程中图像像素和二维特征点是已知的。对于共面标定提出了一种简单及有效的方法去标定摄像机参数。即使用帧缓存中的计算机阵列图像直接来标定参数。首先采用预标定的方法标定出图像中心位置,然后根据帧存图像坐标和世界坐标之间的对应关系使用正交矩阵的约束条件来求解,在此算法中假设尺度因子为1,并且不考虑透镜畸变。所提出的算法用数字仿真图像及真实的图像检验。结果显示,所提出的算法具有较好的精度,是一种简单有效的标定方法。     

Design and Calibration of an Opto-mechanical Appliance for 3D Non-contact Orthopedic Measurements Part II: Calibration Methodology and Experimental Results

A multistep iterative calibration methodology for the opto-mechanical system introduced in Part I is proposed. The methodology makes use of a monoview coplanar set of control points, whose number has been determined on the basis of both geometrical considerations and the results of a statistical analysis aiming at assessing the procedure stability in the case of noisy image data. The calibration procedure is carried out comparing the theoretical and observed images of the calibration pattern. Both synthetic and real data have been employed to test the calibration procedure, which proved to be accurate and efficient. The experimental results achieved by the calibrated system are satisfactory in terms of measurement precision.     

Implicit and explicit camera calibration: theory and experiments

By implicit camera calibration, we mean the process of calibrating a camera without explicitly computing its physical parameters. Implicit calibration can be used for both three-dimensional (3-D) measurement and generation of image coordinates. In this paper, we present a new implicit model based on the generalized projective mappings between the image plane and two calibration planes. The back-projection and projection processes are modelled separately to ease the computation of distorted image coordinates from known world points. A set of constraints of perspectivity is derived to relate the transformation parameters of the two calibration planes. Under the assumption of the radial distortion model, we present a computationally efficient method for explicitly correcting the distortion of image coordinates in frame buffer without involving the computation of camera position and orientation. By combining with any linear calibration techniques, this method makes explicit the camera physical parameters. Extensive experimental comparison of our methods with the classic photogrammetric method and Tsai's (1986) method in the aspects of 3-D measurement (both absolute and relative errors), the prediction of image coordinates, and the effect of the number of calibration points, is made using real images from 15 different depth values     

基于投影变换的图像测量系统标定

图像测量系统标定是计算机视觉获取三维信息的前提和基础。为了进一步提高标定精度和速度,提出了一种新的基于投影变换标定法。首先,构造模版图像,将该图像经投影变换得到无畸变图像,然后,将其与由原始图像经消除畸变后所得的无畸变图像进行对比,通过差值来确定畸变模型系数。在求出畸变模型的基础上,再求解其他相机参数。该方法迴避了传统方法繁多的迭代步骤,避免了由于初始参数的估计不准所产生的误差,具有直观、精确和相对快速等优点。并通过实验仿真,验证了该算法的可行性与准确性。