Omnidirectional Imaging System Research Articles

단일카메라 전방향 스테레오 비전 시스템을 이용한 거리측정

It is possible to obtain an omnidirectional stereo image via a single camera by using a catadioptric approach with a convex mirror and concave lens. In order to measure three-dimensional distance using the imaging system, the optical parameters of the system are required. In this paper, a calibration procedure to extract the parameters of the imaging system is described. Based on the parameters, experiments are carried out to verify the performance of the three-dimensional distance measurement of a single camera omnidirectional stereo imaging system.

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.

A Survey of Catadioptric Omnidirectional Camera Calibration

For dozen years, computer vision becomes more popular, in which omnidirectional camera has a larger field of view and widely been used in many fields, such as: robot navigation, visual surveillance, virtual reality, three-dimensional reconstruction, and so on. Camera calibration is an essential step to obtain three- dimensional geometric information from a two- dimensional image. Meanwhile, the omnidirectional camera image has catadioptric distortion, which need to be corrected in many applications, thus the study of such camera calibration method has important theoretical significance and practical applications. This paper firstly introduces the research status of catadioptric omnidirectional imaging system; then the image formation process of catadioptric omnidirectional imaging system has been given; finally a simple classification of omnidirectional imaging method is given, and we discussed the advantages and disadvantages of these methods.

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.

구조광 영상기반 전방향 거리측정 시스템 개발

In this paper, a ranging system is proposed that is able to measure 360 degree omnidirectional distances to environment objects. The ranging system is based on the structured light imaging system with catadioptric omnidirectional mirror. In order to make the ranging system robust against environmental illumination, efficient structured light image processing algorithms are developed; sequential integration of difference images with modulated structured light and radial search based on Bresenham line drawing algorithm. A dedicated FPGA image processor is developed to speed up the overall image processing. Also the distance equation is derived in the omnidirectional imaging system with a hyperbolic mirror. It is expected that the omnidirectional ranging system is useful for mapping and localization of mobile robot. Experiments are carried out to verify the performance of the proposed ranging system.

去散焦模糊的折反射全向成像系统设计

去散焦模糊的折反射全向成像系统设计

Difference analysis and registration research of a pair of complementary cylindrical panoramic images

Based on the introduction of the complementary catadioptric omnidirectional imaging system,the difference between correspondence points in two complementary cylindrical panoramic images was analyzed in detail.For the coordinate difference of correspondence points in two images,Harris corner was chosen to search transform model of registration,to solve the registration problem of the two complementary cylindrical panoramic images.The experimental results cover the registration results,precision of using affine model,projective model and polynomial model for registration,which suggest that third-order polynomials model is more suitable.

双反射面互补结构的折反射全向成像系统设计

双反射面互补结构的折反射全向成像系统设计

Spectral Analysis of Omnidirectional Illumination in a Natural Scene

This article describes a method for analyzing omnidirectional color signals in a natural scene, which contains direct illuminations of daylights and indirect illuminations of the reflected lights from different object surfaces. A multiband omnidirectional imaging system is used for capturing high resolution images in the omnidirectional observations at a particular point in a natural scene. The spectral-power distributions of color signals are recovered from the captured six-band images. The authors investigate the spectral composition of the omnidirectional scene illumination based on the principal component analysis of the whole set of color signals acquired at the same location in a fixed time of day in five months of a year. It is found that all the omnidirectional color signals can be expressed in a linear combination of only three principal components. This property has the potential for high data compression. Moreover, the authors analyze the chromaticity distribution of omnidirectional color signals. Experimental results are presented for omnidirectional color signals obtained in an outdoor scene of university campus. The reliability of the proposed method is examined from various points of view. An application to image rendering is shown.

A High-Resolution Imaging System for Omnidirectional Illuminant Estimation

Illuminant estimation in natural scenes includes the problem of estimating a spatial distribution of light sources by omnidirectional observations. So far most omnidirectional measuring systems used a mirrored ball as an optical tool. This kind of system, however, has several essential problems, such as low and nonuniform spatial resolution and a dead region due to imaging the camera itself, as reflected by the mirror. The present article realizes multiband spectral imaging with high spatial resolution for omnidirectional estimation of scene illuminant in a simple measuring system. To overcome the mirrored ball problems, we propose a multiband omnidirectional imaging system using a high-resolution trichromatic digital camera, a fisheye lens, and two commercial color filters. The spatial resolution of omnidirectional imaging systems is analyzed based on an optics model in detail. We describe a practical spectral imaging system. Use of the RGB camera with each of the two color filters allows two different sets of trichromatic spectral sensitivity functions via spectral multiplication, resulting in six spectral bands, after image capture with each color filter. An algorithm is developed based on statistical estimation theory for estimating illuminant spectra from noisy observations of the sensor outputs. The feasibility of the proposed method is examined from the viewpoints of spatial resolution and omnidirectional illuminant estimation.

Low-cost method for the estimation of the shape of quadric mirrors and calibration of catadioptric cameras

This paper tackles the problem of quadric mirror estimation for omnidirectional imaging systems, as well as the poses of the camera relative to the mirror and to the world reference system. These estimates are obtained for quadric-shaped mirrors (including elliptic, parabolic, hyperbolic, and spherical mirrors) where the positions of the camera and mirror are unconstrained (fully noncentral configurations). The apparent contour of the mirror can be used to reduce the uncertainty in the estimation. Although it can enhance both the accuracy of the estimation (allowing the method to converge from farther initial configurations) and also its performance, its use is not strictly required. The intrinsic parameters of the camera model (pinhole or orthographic) are assumed to be known, as well as the structure of a calibration object in local coordinates. The method is nonlinear, and we use a genetic algorithm in conjunction with the Nelder-Mead simplex algorithm to minimize the objective function. Experimental results using real data are presented, demonstrating the accuracy of this calibration method, comparing its accuracy with and without the apparent contour, and computing its reprojection error. Because the mirror quadric is estimated, this method can also be used to identify and classify the mirror.

Hybrid Stereo Configurations Through a Cylindrical Sensor Calibration

This paper deals with the calibration of a cylindric omnidirectional imaging system, based on a rotating 2,048 pixels linear camera which provides high definition panoramas. The two-step algorithm relies on line-segment projections as calibration features, which are sinusoidal curves. We proposed a cylindrical line detection, based on the dual principle of the Hough transform. Moreover, the use of Plucker coordinates introduces some new characteristics in the calibration process. This kind of formalism allow a linearization of the cylindrical projection, which is non-linear in the usual way. Results obtained from this first step are used to evaluate one of the intrinsics, the other one being determined by a linear criterion minimization in the dual space, i.e. the sines magnitudes space.

Panoramic stereo reconstruction using non-SVP optics

Omni-directional sensors are useful in obtaining a 360° field of view with a single lens camera. Omni-directional stereo imaging systems can be constructed using a single camera and a mirror consisting of two concentric, radially symmetric lobes. If the central camera-mirror axis is vertical, a stereo image containing imagery from all azimuth directions from two viewpoints can be captured within one image. A vertically oriented catadioptric optical system that employs a mirror with a radial profile other than parabolic or hyperbolic cannot maintain the straightness of non-vertical lines. However, non-parabolic or hyperbolic mirror profiles are desirable for resolution distribution, sensor size, and cost. These mirror shapes, including spherical mirrors, are said to be non-central or non-single view-point (SVP); without a virtual perspective point, they pose new feature extraction challenges. The projection of straight lines in the world do not map to straight lines on the pixel array for non-SVP panoramic images, nor in the general case map to any conventional conic. A method for processing the imagery from a panoramic non-SVP catadioptric stereo sensor to reconstruct a 3D model of polyhedral objects with horizontal and vertical line edges is introduced. Horizontal line segments are extracted using the Panoramic Hough Transform and vertical line segments are recognized as straight radial lines. These segments, and closed shapes they form, are matched between the two lobe views to estimate position in three-dimensions. A novel Hough transform technique is described, and practical considerations for its successful use are explored. Four general weaknesses with Hough transform techniques in general are identified, and solutions to address them in each case are given. Details of a complete system using the Panoramic Hough Transform are given to demonstrate where this transform must be supplemented with other methods for robust operation. Issues of reconstruction accuracy are addressed, and experimental results with synthetic and real images are presented.

Omni-directional visual surveillance

Perimeter security generally requires watching areas that afford trespassers reasonable cover and concealment. By definition, such ‘interesting’ areas have limited visibility distance. Furthermore, targets of interest generally attempt to conceal themselves within the cover, sometimes adding camouflage to further reduce their visibility. Such targets are only visible while in motion. The combined result of limited visibility and target visibility severely reduces the usefulness of any approach using a standard Pan/Tilt/Zoom (PTZ) camera. As a result, these situations call for a very sensitive system with a wide field of view, and are a natural application for Omni-directional Video Surveillance and Monitoring. This paper describes a frame-rate, low-power, omni-directional tracking system (LOTS). The paper discusses related background work including resolution issues in omni-directional imaging. One of the novel system component details is quasi-connected-components (QCC). QCC combines gap filling, thresholding-with-hysteresis (TWH) and a novel region merging/cleaning approach. The multi-background modeling and dynamic thresholding make an ideal approach for difficult situations like outdoor tracking in high clutter. The paper also describes target geolocation and issues in the system user interface. The single viewpoint property of the omni-directional imaging system used simplifies the backprojection and unwarping. We end with a summary of an external evaluation of an early form of the system and comments about recent work and field tests.