Continuous localization and mapping of a pan–tilt–zoom camera for wide area tracking

Pan–tilt–zoom (PTZ) cameras are well suited for object identification and recognition in far-field scenes. However, the effective use of PTZ cameras is complicated by the fact that a continuous online camera calibration is needed and the absolute pan, tilt and zoom values provided by the camera actuators cannot be used because they are not synchronized with the video stream. So, accurate calibration must be directly extracted from the visual content of the frames. Moreover, the large and abrupt scale changes, the scene background changes due to the camera operation and the need of camera motion compensation make target tracking with these cameras extremely challenging. In this paper, we present a solution that provides continuous online calibration of PTZ cameras which is robust to rapid camera motion, changes of the environment due to varying illumination or moving objects. The approach also scales beyond thousands of scene landmarks extracted with the SURF keypoint detector. The method directly derives the relationship between the position of a target in the ground plane and the corresponding scale and position in the image and allows real-time tracking of multiple targets with high and stable degree of accuracy even at far distances and any zoom level.     

Automatic camera control in virtual environments augmented using multiple sparse videos

Automated virtual camera control has been widely used in animation and interactive virtual environments. We have developed a multiple sparse camera based free view video system prototype that allows users to control the position and orientation of a virtual camera, enabling the observation of a real scene in three dimensions (3D) from any desired viewpoint. Automatic camera control can be activated to follow selected objects by the user. Our method combines a simple geometric model of the scene composed of planes (virtual environment), augmented with visual information from the cameras and pre-computed tracking information of moving targets to generate novel perspective corrected 3D views of the virtual camera and moving objects. To achieve real-time rendering performance, view-dependent textured mapped billboards are used to render the moving objects at their correct locations and foreground masks are used to remove the moving objects from the projected video streams. The current prototype runs on a PC with a common graphics card and can generate virtual 2D views from three cameras of resolution 768×576 with several moving objects at about 11 fps.     

一种基于TOF相机与CCD相机的联合标定算法研究

针对基于Time-of-Flight(TOF)相机的彩色目标三维重建需标定CCD相机与TOF相机联合系统的几何参数,在研究现有的基于彩色图像和TOF深度图像标定算法的基础上,提出了一种基于平面棋盘模板的标定方法。拍摄了固定在平面标定模板上的彩色棋盘图案在不同角度下的彩色图像和振幅图像,改进了Harris角点提取,根据棋盘格上角点与虚拟像点的共轭关系,建立了相机标定系统模型,利用Levenberg-Marquardt算法求解,进行了标定实验。获取了TOF与CCD相机内参数,并利用像平面之间的位姿关系估计两相机坐标系的相对姿态,最后进行联合优化,获取了相机之间的旋转矩阵与平移向量。实验结果表明,提出的算法优化了求解过程,提高了标定效率,能够获得较高的精度。     

立体图像对的生成

获取同一场景的立体图像对是实现双目立体成像的一个关键问题。提出了一种在三维场景已经建好的情况下生成立体图像对的方法。该方法根据双目立体视觉的原理，利用3DS MAX中的摄像机对象对场景中的物体进行坐标变换和透视投影变换，分别生成左眼视图和右眼视图。实验结果表明，两个目标摄像机与三维模型的位置关系以及基线长度是影响立体效果的重要因素，改变目标摄像机与三维模型的位置，可以分别生成正视差、负视差的立体图像对，当AB与CO的比例参数为0.05时，生成的立体图像对的立体效果较佳。     

Monitoring activities from multiple video streams: establishing acommon coordinate frame

Monitoring of large sites requires coordination between multiple cameras, which in turn requires methods for relating events between distributed cameras. This paper tackles the problem of automatic external calibration of multiple cameras in an extended scene, that is, full recovery of their 3D relative positions and orientations. Because the cameras are placed far apart, brightness or proximity constraints cannot be used to match static features, so we instead apply planar geometric constraints to moving objects tracked throughout the scene. By robustly matching and fitting tracked objects to a planar model, we align the scene's ground plane across multiple views and decompose the planar alignment matrix to recover the 3D relative camera and ground plane positions. We demonstrate this technique in both a controlled lab setting where we test the effects of errors in the intrinsic camera parameters, and in an uncontrolled, outdoor setting. In the latter, we do not assume synchronized cameras and we show that enforcing geometric constraints enables us to align the tracking data in time. In spite of noise in the intrinsic camera parameters and in the image data, the system successfully transforms multiple views of the scene's ground plane to an overhead view and recovers the relative 3D camera and ground plane positions     

Tri-view morphing

This paper presents an efficient image-based approach to navigate a scene based on only three wide-baseline uncalibrated images without the explicit use of a 3D model. After automatically recovering corresponding points between each pair of images, an accurate trifocal plane is extracted from the trifocal tensor of these three images. Next, based on a small number of feature marks using a friendly GUI, the correct dense disparity maps are obtained by using our trinocular-stereo algorithm. Employing the barycentric warping scheme with the computed disparity, we can generate an arbitrary novel view within a triangle spanned by three camera centers. Furthermore, after self-calibration of the cameras, 3D objects can be correctly augmented into the virtual environment synthesized by the tri-view morphing algorithm. Three applications of the tri-view morphing algorithm are demonstrated. The first one is 4D video synthesis, which can be used to fill in the gap between a few sparsely located video cameras to synthetically generate a video from a virtual moving camera. This synthetic camera can be used to view the dynamic scene from a novel view instead of the original static camera views. The second application is multiple view morphing, where we can seamlessly fly through the scene over a 2D space constructed by more than three cameras. The last one is dynamic scene synthesis using three still images, where several rigid objects may move in any orientation or direction. After segmenting three reference frames into several layers, the novel views in the dynamic scene can be generated by applying our algorithm. Finally, the experiments are presented to illustrate that a series of photo-realistic virtual views can be generated to fly through a virtual environment covered by several static cameras.     

Single view compositing with shadows

In this paper, we describe how geometrically correct and visually realistic shadows may be computed for objects composited into a single view of a target scene. Compared to traditional single view compositing methods, which either do not deal with the shadow effects or manually create the shadows for the composited objects, our approach efficiently utilizes the geometric and photometric constraints extracted from a single target image to synthesize the shadows consistent with the overall target scene for the inserted objects. In particular, we explore (i) the constraints provided by imaged scene structure, e.g. vanishing points of orthogonal directions, for camera calibration and thus explicit determination of the locations of the camera and the light source; (ii) the relatively weaker geometric constraint, the planar homology, that models the imaged shadow relations when explicit camera calibration is not possible; and (iii) the photometric constraints that are required to match the color characteristics of the synthesized shadows with those of the original scene. For each constraint, we demonstrate the working examples followed by our observations. To show the accuracy and the applications of the proposed method, we present the results for a variety of target scenes, including footage from commercial Hollywood movies and 3D video games.     

The invariant features-based target tracking across multiple cameras

Target tracking across lenses is a popular research topic for video surveillance recently. This paper presents a method of target tracking across lenses with overlap regions. First, the target detection and tracking are completed with a single camera. Second, in order to obtain the location-invariant feature of the same target in the images with various cameras, the camera calibration is completed based on a three-dimension (3D) model. After that, for all images via multiple cameras, the coordinates of the 3D model are unified. Finally, referring to the assumption of spatial and temporal consistency of the target location across multiple cameras, the association among detected objects for the same target with different cameras is established. And a feature pool is built which contains perspective and scale features. Thus the same target is continuously tracked across multiple lenses. At last, the performance of the proposed approach is compared with KSP and PABC and demonstrated with indoor and outdoor experiments.     

基于数字CCD相机的高速图像采集系统

介绍了一种基于线阵CCD相机的高速数据采集的方法和系统,该系统采用双CCD相机进行布站并对过靶物体进行拍摄,通过图像采集卡实现计算机对CCD相机的控制,并且完成数据的采集和存储,能够成功运用到高速运动物体的空间位置和速度检测方面,经试验,其实时性和高精度性能使其很好地应用到靶场的立靶精度试验中,极大地提高了靶场试验效果。     

Assessing the influence of temperature variations on the geometrical properties of a low-cost calibrated camera system by using computer vision procedures

This paper estimates temperature influence on geometrical properties of both a single camera and a calibrated camera system, assuming low-cost CCD cameras. It does not cover the effect of temperature on the camera’s electronics. Firstly, the influence of temperature change on camera parameters was modelled and integrated into an existing analytical camera model. A modified camera model enables quantitative assessment regarding the influence of temperature variations for a single camera. Temperature variations also directly influence the accuracies of calibrated cameras. The inability to analytically determine the calibration method error magnitude, led us to experimentally estimate errors regarding calibrated cameras. Finally, the total error regarding calibrated cameras was derived by combining the numerical error of the calibration method with those errors originating from temperature variations. The results show that the influence of temperature variations decreases when increasing the distances of the observed objects from the cameras. On a typical building site, the temperature influence is reflected in the image as an error of less than one pixel.     

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.     

Autocalibration with the Minimum Number of Cameras with Known Pixel Shape

In 3D reconstruction, the recovery of the calibration parameters of the cameras is paramount since it provides metric information about the observed scene, e.g., measures of angles and ratios of distances. Autocalibration enables the estimation of the camera parameters without using a calibration device, but by enforcing simple constraints on the camera parameters. In the absence of information about the internal camera parameters such as the focal length and the principal point, the knowledge of the camera pixel shape is usually the only available constraint. Given a projective reconstruction of a rigid scene, we address the problem of the autocalibration of a minimal set of cameras with known pixel shape and otherwise arbitrarily varying intrinsic and extrinsic parameters. We propose an algorithm that only requires 5 cameras (the theoretical minimum), thus halving the number of cameras required by previous algorithms based on the same constraint. To this purpose, we introduce as our basic geometric tool the six-line conic variety (SLCV), consisting in the set of planes intersecting six given lines of 3D space in points of a conic. We show that the set of solutions of the Euclidean upgrading problem for three cameras with known pixel shape can be parameterized in a computationally efficient way. This parameterization is then used to solve autocalibration from five or more cameras, reducing the three-dimensional search space to a two-dimensional one. We provide experiments with real images showing the good performance of the technique.     

基于CCD摄像机的测控装备标校系统的设计与实现

为了实现测控装备的标校,目标观察与监视,实时记录视频图像的功能,设计了基于CCD摄像机测控装备标校系统.该系统在镜头组合、标校处理器、主控计算机等硬件基础上,基于VC＋＋开发了标校软件,研制了测控装备标校系统.本系统能够成功实现标校,目标观察与监视、记录视频图像等功能.实践证明该系统运行稳定,很好的完成了上述功能.     

A Video-Based 3D-Reconstruction of Soccer Games

In this paper we present SoccerMan, a reconstruction system designed to generate animated, virtual 3D views from two synchronous video sequences of a short part of a given soccer game. After the reconstruction process, which needs also some manual interaction, the virtual 3D scene can be examined and 'replayed' from any viewpoint. Players are modeled as so-called animated texture objects, i.e. 2D player shapes are extracted from video and texture-mapped onto rectangles in 3D space. Animated texture objects have shown very appropriate as a 3D representation of soccer players in motion, as the visual nature of the original human motion is preserved. The trajectories of the players and the ball in 3D space are reconstructed accurately. In order to create a 3D reconstruction of a given soccer scene, the following steps have to be executed: 1) Camera parameters of all frames of both sequences are computed (camera calibration). 2) The playground texture is extracted from the video sequences. 3) Trajectories of the ball and the players' heads are computed after manually specifying their image positions in a few key frames. 4) Player textures are extracted automatically from video. 5) The shapes of colliding or occluding players are separated automatically. 6) For visualization, player shapes are texture-mapped onto appropriately placed rectangles in virtual space. SoccerMan is a novel experimental sports analysis system with fairly ambitious objectives. Its design decisions, in particular to start from two synchronous video sequences and to model players by texture objects, have already proven promising.     

TransCAIP: A Live 3D TV System Using a Camera Array and an Integral Photography Display with Interactive Control of Viewing Parameters

The system described in this paper provides a real-time 3D visual experience by using an array of 64 video cameras and an integral photography display with 60 viewing directions. The live 3D scene in front of the camera array is reproduced by the full-color, full-parallax autostereoscopic display with interactive control of viewing parameters. The main technical challenge is fast and flexible conversion of the data from the 64 multicamera images to the integral photography format. Based on image-based rendering techniques, our conversion method first renders 60 novel images corresponding to the viewing directions of the display, and then arranges the rendered pixels to produce an integral photography image. For real-time processing on a single PC, all the conversion processes are implemented on a GPU with GPGPU techniques. The conversion method also allows a user to interactively control viewing parameters of the displayed image for reproducing the dynamic 3D scene with desirable parameters. This control is performed as a software process, without reconfiguring the hardware system, by changing the rendering parameters such as the convergence point of the rendering cameras and the interval between the viewpoints of the rendering cameras.     

基于多摄像位的空间定位系统的研究与设计

基于多摄像位的空间定位即从来自多个摄像位的视频截图中获取物体的空间三维几何信息。本系统主要由三个部分构成,分别是:摄像机标定部分、立体匹配部分、基于点的三维重建部分。本文主要围绕这几个部分展开研究:首先,在摄像机参数标定中,采用正友的基于平面标定模板的摄像机标定方法,通过实验和计算获取摄像机的参数;其次,立体匹配部分采用了Burchfield算法,试验结果得到了视差图;最后,最后根据立体视觉基本原理,完成了三维坐标计算,得到了一个特定区域的点集信息(如球类)。本文最终设计并实现了一个应用于体育节目包装的基于多摄像位的空间定位系统。     

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.     

一种水下运动物体三维轨迹视觉测量方法

针对海洋工程中采用的设备深海悬垂法安装过程,采用多摄像头视频运动分析方 法计算水下三维运动轨迹可用于指导海洋工程的结构安装和分析设备水下运动特征。水下视频 和图像的处理获取面临着诸多挑战,首先由于水下环境悬浮物和颗粒较多,光在水下发生了散 射,使水下图像发生了退化;其次水下视频运动分析遇到的一个主要障碍是光线的折射引起的 图像误差。由于光在水、玻璃、空气不同介质间发生折射,光路发生弯曲,陆地上的摄像机成 像模型在水中不再适用,需要提出新的水下摄像机成像模型。本文引入带光线折射的水下摄像 机成像模型,研究水下摄像机的内参数和外参数标定方法,利用固定布置的 3 个水下摄像机拍 摄的目标水下运动视频来计算水下目标的轨迹。该方法适用于水池环境下水下物体大范围运动, 可以得到较为精确的轨迹,并得到了实验验证。     

Automated camera planning to film robot operations

Automatic 3D animation generation techniques are becoming increasingly popular in different areas related to computer graphics such as video games and animated movies. They help automate the filmmaking process even by non professionals without or with minimal intervention of animators and computer graphics programmers. Based on specified cinematographic principles and filming rules, they plan the sequence of virtual cameras that the best render a 3D scene. In this paper, we present an approach for automatic movie generation using linear temporal logic to express these filming and cinematography rules. We consider the filming of a 3D scene as a sequence of shots satisfying given filming rules, conveying constraints on the desirable configuration (position, orientation, and zoom) of virtual cameras. The selection of camera configurations at different points in time is understood as a camera plan, which is computed using a temporal-logic based planning system (TLPlan) to obtain a 3D movie. The camera planner is used within an automated planning application for generating 3D tasks demonstrations involving a teleoperated robot arm on the the International Space Station (ISS). A typical task demonstration involves moving the robot arm from one configuration to another. The main challenge is to automatically plan the configurations of virtual cameras to film the arm in a manner that conveys the best awareness of the robot trajectory to the user. The robot trajectory is generated using a path-planner. The camera planner is then invoked to find a sequence of configurations of virtual cameras to film the trajectory.