Defocus deblurring for catadioptric omnidirectional imaging based on spatially invariant point spread function

The problem of catadioptric omnidirectional imaging defocus blur, which is caused by lens aperture and mirror curvature, becomes more severe when high resolution sensors and large apertures are applied. In order to overcome this problem, a novel method based on computational photography is proposed. Firstly, the defocus blur of catadioptric omnidirectional imaging is analyzed to calculate the point spread function for different scene points. Then, the defocus blur kernel of omnidirectional image is confirmed to be spatially invariant when rotating the focus ring of camera lens during an image’s integration time. Lastly, the deconvolution algorithm using prior sparse derivatives is applied to obtain all-focused/sharp omnidirectional images. Experimental results demonstrate that the proposed method is effective for omnidirectional image deblurring and can be applied to most existing catadioptric omnidirectional imaging systems.     

现场勘察中广角镜头相机快速标定算法及实现

基于摄影资料的图像测距技术已广泛应用于交通事故、考古等不可复原的现场勘察工作中,利用普通相机进行摄影测量也日趋成熟。但是普通相机没有广角镜头相机的取景优势,现场分析也比较局限,因此广角镜头相机逐渐取代普通相机。而广角镜头相机容易产生图像畸变效应。为此,本文基于相机成像原理,通过精确网格模板标定图像,利用相机参数间物理关系计算出相机内参和畸变参数,提出了一种广角镜头相机的快速标定算法,结合拍摄现场图像,精确定位参考模板标志牌在照片中的成像结果,计算出广角镜头相机的外参,建立广角镜头相机摄影测量系统。现场实验应用表明,本算法标定快速、简单、测量精度高,可以应用于交通事故现场勘测。     

Wide-angle catadioptric lens with a rectilinear projection scheme

A catadioptric wide-angle lens having a rectilinear projection scheme has been developed with a view to possible applications in the security-surveillance area. The lens has been designed for a miniature camera with a video graphics array-grade 1/3 in. color CCD sensor. The field of view of the lens is over 151 degrees , and still distortion is under 1%. Furthermore, the modulation transfer function is better than 0.3 at 70 line pairs/mm over the whole active area of the image sensor.     

柱面场景无畸变的折反射全景成像系统

提出了一种基于透视成像模型的柱面场景无畸变的折反射全景成像系统设计方法,该方法 利用系统柱面场景无畸变成像要求和视场角确定反射镜面形。根据这一方法设计制作了高次旋转对称非球面反射镜,并用该反射镜和CCD摄像头建立了全景成像系统,实现了对360°柱面场景的无畸变成像。     

摄像机径向畸变校正和内参估计的单图标定方法

提出了一种对摄像机的径向畸变进行校正和内参数估计的单图标定方法.拍摄一幅平面标定模板图像,提出若干条直线,拟合在单参数除法畸变模型下的圆弧参数,从而估计出径向畸变.对径向畸变进行校正后,利用标定模板点与经过校正后的图像点之间的对应关系,估计出单应性矩阵.在假定摄像机主点与畸变中心重合的条件下,线性地计算出摄像机焦距初值.以上述线性方法得到的结果为初值,进行非线性优化,最终得到准确的摄像机参数.超广角鱼眼相机和普通数码相机的实验结果表明,本文提出的算法实现简单、适用性广,结果准确,具有较强的实用性.     

Real-time pickup method for a three-dimensional image based on integral photography

We studied integral photography (IP), which creates three-dimensional autostereoscopic images. In particular we studied the possibility of a new method that uses a television camera to shoot directly numerous real images produced by a lens array. Unlike the conventional IP method in which the film is placed immediately behind a lens array, this method employs a television camera, which enables us to shoot moving pictures. Of a number of factors affecting the process of image pickup, we examined some optical factors and compared them with those obtained by the conventional IP method. The results show that with this new direct pickup method that uses a television camera, we can obtain an IP image like those obtained by using the conventional IP method. Further, we conducted an experiment with an high-definition TV camera, confirming the production of an autostereoscopic image by using a display device that combines a liquid-crystal panel and pinholes.     

一次成像折反射式步进变焦距物镜

设计了一个用于远距离监视电视的折反射式步进变焦距透镜。为使微光、白光和近红外三个波段共用一个光学系统,提出一次成像折反射式变焦,并进行了理论分析和给出了设计实例。克服了二次成像折反射式步进变焦方式二级光谱不能校正的缺陷,并且杜绝了像面中心产生黑斑的可能,结构也比较简单。     

An ultrashort throw ratio projection lens design based on a catadioptric structure

In this paper, we present a rotational symmetry for an ultrashort throw (UST) lens with offset field. The UST lens has a throw ratio of 0.23 and a total track of 195 mm. The optical elements of the UST lens are comprised of two parts. First, a catadioptric projection lens where the catadioptric function permits reaching an ultrashort throw ratio, short total track, while at the same time requiring fewer lens elements. The second part is a collimating lens which takes advantage of the telecentric condition to generate uniform total internal reflection (TIR) in the TIR prism. With this design, an effective focal length of -1.96 mm and a f-number of 2.4 can be obtained. The root mean square spot size and lateral colour of all fields are smaller than one pixel in size. The maximum optical distortion of ?0.97% and TV distortion of 0.2% are acceptable. In terms of image quality, the modulation transfer function (MTF) values for all fields are above 0.65 at 0.245 line pairs/mm. Even when the tolerance error is considered, the MTF values for all fields are still above 0.3. The suitability of the novel UST lens design for projection applications is discussed.     

增强现实技术在远程现实中的应用研究

设计了基于移动机器人的远程现实系统,辅助机器人遥操作.为提高人机交互能力,把增强现实技术应用到远程现实当中,根据增强现实中三维注册的原理,推导了双曲面全景成像中基于视觉的注册算法,实现了三维虚拟机器人在全景图像中的注册定位.为了提供更加直观的人机交互界面,采用一种快速算法把圆形全景图进行近似的柱面展开,并将"增强远程现实"应用于展开的图像界面中.实验结果表明,增强远程现实改善了场景的视觉感官效果、增加了辅助信息,提高了人机交互能力.     

Optimization method for ultra-wide-angle and panoramic optical systems

To an ultra-wide-angle and panoramic optical system, the aberrations of point object at any field angle are separated into two types: the aperture-ray aberrations of off-axis point object and the chief-ray aberrations. A simple form of the triangular formulae of tracing an oblique-incidence ray is derived to calculate the chief-ray parameters and their aberrations; moreover, the aperture-ray aberrations of an off-axis point object are analyzed with the plane-symmetric aberration theory. Based on the two types of aberrations, we present a merit function for ultra-wide-angle and panoramic optical systems; the optimization program with the differential-evolution algorithm is then developed. To validate the optimization method we finally optimize a fish-eye lens and a catadioptric omnidirectional imaging system.     

A two-point spatial mapping method for hybrid vision systems

We propose a new spatial mapping method for hybrid vision systems consisting of an omnidirectional camera and an active perspective camera. We calculate the relative position between the optical centers of the two cameras based on pre-acquisition parameters of two sample points from the observed scene, avoiding the difficulty and error in direct measurement, and at the same time using fewer points. We derive the formula of the relative position between the omnidirectional camera’s optical center and the active camera’s optical center from the distance between two points, and give a method for calculating the corresponding pan and tilt angles of the active camera from the coordinates in the omnidirectional image. Simulation and real experiments show that the two-point spatial mapping method has higher estimation accuracy than the homography calibration method, and at the same time has higher consistency among test points.     

Depth recovery and refinement from a single image using defocus cues

We present a technique to recover and refine the depth map from a single image captured by a conventional camera in this paper. Our method builds on the universal imaging principle: only scene at the focus distance will converge to a single sharp point on imaging sensor but other scene will yield different blur effects varying with its distance from the camera lens. We first estimate depth values at edge locations via spectrum contrast and then recover the full depth map using a depth matting optimization method. Due to the fact that some blur textures such as soft shadows or blur patterns will produce ambiguity results during the procedure of depth estimation, we use a total variation-based image smoothing method to smooth the original image, a smoothed image with detailed texture being suppressed can be generated. Taking this smoothed image as reference image, a guided filter is used to refine the final depth map.     

全球面无死角的全方位视觉传感器的设计

为了获取整个球面全景图像,提出了全方位视觉传感器(omni-directional vision sensor,ODVS)的二次折反射的成像原理并设计了折反射镜面.利用4阶Runge-Kutta算法求得了镜面曲面的数值解,通过组合镜头的设计实现ODVS与广角镜头的集成以消除ODVS的固有死角,然后,将两台无死角的ODVS装置以背靠背的方式进行连接,并将所获取的全景视频图像进行展开及无缝拼接得到360°* 360°视频图像.实验结果表明,所设计的ODVS装置可以获取全球面的视场范围,在视频监控领域有重要的应用价值.     

A triangle mesh-based corner detection algorithm for catadioptric images

As with conventional images corner detection is an important aspect of many computer vision problems involving catadioptric images. However, classical image processing algorithms are no longer appropriate for catadioptric images due to nonuniform resolution and distortions of catadioptric images. In this paper, we propose a novel approach to corner detection for catadioptric images based on triangle mesh. First, we transform catadioptric images to spherical images by combining an improved projection model for central catadioptric cameras with triangle mesh for a unit sphere. Spherical images yield a spatially uniform resolution domain for processing catadioptric images. Then, based on the topology of a triangle mesh, variations of light intensity with respect to directions for each image patch are measured to detect corners. The proposed algorithm addresses problems of catadioptric image processing caused by non-uniform resolution and distortions of these images. Experimental results showed that comparing to widely used methods, the triangle mesh-based corner detection algorithm can achieve higher repeatability rate relative to different imaging condition changes.     

Folded catadioptric panoramic lens with an equidistance projection scheme

A new formula for a catadioptric panoramic lens with an equidistance projection scheme has been derived. The fabricated lens has a field of view that is wider than that of any previously reported panoramic lens, and the nonimaged region near the back of the camera has a constant volume with zero angular extension.     

Scheimpflug and high-resolution magnetic resonance imaging of the anterior segment: a comparative study

High-resolution imaging with a camera system built on the Scheimpflug principle has been used to characterize the geometry of the anterior segment of the adult human eye as a function of aging and accommodative state but is critically dependent on algorithms for correction of distortion. High-resolution magnetic resonance imaging (MRI), in contrast, provides lower-resolution information about the adult eye but is undistorted. To test the accuracy of the Scheimpflug correction methods used by Cook and Koretz [J. Opt. Soc. Am. A 15, 1473 (1998)]; [Appl. Opt. 30, 2088 (1991)], data on anterior chamber and segment lengths, as well as lens thickness and anterior and posterior curvatures, were compared with corresponding MRI data for adults aged 18-50 at 0 diopter accommodation. Excellent statistical agreement was found between the MRI and the Scheimpflug data sets with the exception of the posterior lens radius of curvature, which is less well defined than the other measurements in the Scheimpflug images. The considerable agreement between data obtained with MR and Scheimpflug imaging, two different yet complementary in vivo imaging techniques, validates the Scheimpflug correction algorithms of Cook and Koretz and suggests the capability of directly integrating information from both. A third, equivalent, data set obtained with a Scheimpflug-style camera system differs considerably from both Scheimpflug and MRI results in magnitude and age dependence, with negative implications for this alternative method and its correction procedures.     

Single-viewpoint, catadioptric cone mirror omnidirectional imaging theory and analysis

A family of catadioptric imaging systems has been developed that can achieve omnidirectional viewing with a single planar imager while still being able to recover perspective images, provided that they satisfy the single-viewpoint (SVP) constraint. It has been shown that the only mirror shapes that can have SVP when paired with a sole focusing planar imager camera are the surfaces of revolution of conic section curves. However, the special case of such a surface, the cone-shaped mirror itself, has not been deemed a viable SVP mirror shape. We present a comprehensive imaging theory of the cone mirror in its SVP configuration. We show that the SVP, cone mirror catadioptric system not only is practical but also has unique advantages for certain applications. The detailed theory explains why and how a practical SVP cone configuration can be set up, the merits and weaknesses of such systems, and how one can remedy the weaknesses to create a workable imaging system. We also derive the tolerance formula for estimating effects of alignment errors. A prototype has been constructed, and experimental results validate our theory.     

光电窥膛光学系统参数优化选择

通过分析炮管内膛影响CCD成像质量的光强，光的均匀性，视场大小和空间分辨力等因素，提出了增大CCD成像镜头的景深对光电窥膛光学系统的光路结构及其参数优化设计的方法，并建立数学模型，提高了CCD摄像机在炮管内膛的成像质量，使图像在亮度，均匀性，色彩和清晰度方面达到很好效果。     

光点位置测量系统摄像镜头设计

针对使用线阵列电荷耦合器件(CCD)的二维位置定位系统中的光学系统的特殊要求,本文提出一种以球面镜作为前组柱面镜作为后组,前组像面作为后组物面的二级成像结构作为线阵CCD的摄像镜头.该镜头使具有相同一维坐标值的点成像为同一条直线,并且具有广角视场,畸变小,成像质量优良等性能特点.对其设计思想、像差特点进行了分析,并给出了f'=.20 mm,2ω=74,畸变小于1.6%的柱面镜摄像镜头实例及其像差和传递函数计算曲线.     

三维重构视觉系统的标定

文章基于改进两步法的标定思想,在三维重构中提出了一种新的视觉系统参数标定与镜头畸变修正方法.该方法根据图像中心附近点畸变量较小的性质,利用中心附近点和全场视点对CCD相机和DLP投影仪的内外部参数标定和镜头畸变修正进行分离.在标定过程中,所设计的带标准圆阵列的靶标和伪随机连续方形编码可以实现特征点的自动识别和匹配.实验表明,该方法能快速、方便地对视觉系统参数进行标定和镜头畸变修正.