Omnidirectional Imaging System Research Articles

A Modified Keystone-Based Forward-Looking Arc Array Synthetic Aperture Radar 3D Imaging Method

An arc array synthetic aperture radar (AA-SAR) is a new type of omnidirectional observation and imaging system. Based on linear array 3D imaging, this paper introduces a keystone algorithm combined with the arc array SAR 2D imaging method and proposes a modified 3D imaging algorithm based on keystone transformation. The first step is to discuss the target azimuth angle, retain the far-field approximation method of the first-order term, analyze the influence of the forward motion of the platform on the along-track position, and realize the two-dimensional focusing of the target slant range-azimuth direction. The second step is to redefine a new azimuth angle variable in the slant-range along-track imaging and use the keystone-based processing algorithm in the range frequency domain to eliminate the coupling term generated by the array angle and the slant-range time. The corrected data are used to perform along-track pulse compression to obtain the focused image of the target and realize the three-dimensional imaging of the target. Finally, in this article, the spatial resolution of the AA-SAR system in the forward-looking state is analyzed in detail, and the change in the spatial resolution of the system and the effectiveness of the algorithm are verified through simulation.

Non-symmetrical five-sided mirrors based single viewpoint catadioptric infrared omnidirectional imaging system

Non-symmetrical five-sided mirrors based single viewpoint catadioptric infrared omnidirectional imaging system

Omnidirectional ghost imaging system and unwrapping-free panoramic ghost imaging.

Ghost imaging (GI) is an unconventional imaging method that reconstructs the object information via light-intensity correlation measurements. However, at present, the field of view (FOV) of this method is limited to the illumination range of light patterns. To enlarge the FOV of GI efficiently, we propose an omnidirectional GI system (OGIS) that can achieve a 360° omnidirectional FOV only via the addition of a curved mirror. The OGIS features retina-like annular patterns designed as a log-polar structure and can obtain the undistorted unwrapping-free panoramic images with uniform resolution. This research presents a new, to the best of our knowledge, perspective for the applications of GI, such as pipeline detection, a panoramic situation awareness for autonomous vehicles.

Design of an omnidirectional gaze optical imaging system with ultrahigh resolution

In this study, we discuss a new method to optimize the design of an omnidirectional gaze optical imaging system with ultrahigh resolution and long focus. An aspheric diffractive optical element is used in the optical system to offer more freedom, simplify the structure, and decrease the chromatic aberration. Owing to large image sensor arrays, the omnidirectional gaze photoelectric imaging system is capable of overcoming the shortcoming of low peripheral resolution. This has led to an increased usage of this system in military applications. Here, we describe a six-piece optical system installed on an 80 MPx full-frame CCD with 10,320 × 7752 pixels, 5.2 μm pixel size, 200° × 360° field of view, and an effective focal length of 11.6 mm. The difficulties in designing an ultrahigh-resolution fish-eye lens have been discussed and addressed. Furthermore, system performance evaluation, tolerance analysis, and image distortion calibration were also performed.

Catadioptric hyperspectral imaging, an unmixing approach

Hyperspectral imaging systems provide dense spectral information on the scene under investigation by collecting data from a high number of contiguous bands of the electromagnetic spectrum. The low spatial resolutions of these sensors frequently give rise to the mixing problem in remote sensing applications. Several unmixing approaches are developed in order to handle the challenging mixing problem on perspective images. On the other hand, omnidirectional imaging systems provide a 360‐degree field of view in a single image at the expense of lower spatial resolution. In this study, we propose a novel imaging system which integrates hyperspectral cameras with mirrors so on to yield catadioptric omnidirectional imaging systems to benefit from the advantages of both modes. Catadioptric images, incorporating a camera with a reflecting device, introduce radial warping depending on the structure of the mirror used in the system. This warping causes a non‐uniformity in the spatial resolution which further complicates the unmixing problem. In this context, a novel spatial–contextual unmixing algorithm specifically for the large field of view of the hyperspectral imaging system is developed. The proposed algorithm is evaluated on various real‐world and simulated cases. The experimental results show that the proposed approach outperforms compared methods.

Real-Time Free-Moving Active Coded Mask 3D Gamma-Ray Imaging

The ability to localize and map the distribution of gamma-ray emitting radionuclides in 3D has applications ranging from medical imaging to nuclear security. In the case of radiological source search and nuclear contamination remediation, the deployment of freely moving detection systems such as handheld instruments or ground/aerial-based vehicles is critical in overcoming the inverse square law and complex shielding scenarios. Using contextual sensors, these systems can simultaneously generate 3D maps of the surrounding environment and track the position and orientation of the gamma-ray sensitive detectors in that environment. The fusion of contextual scene data and gamma-ray detector data to facilitate real-time 3D gamma-ray image reconstruction has been demonstrated with mobile high purity germanium (HPGe) and CdZnTe-based Compton cameras for gamma-ray energies ranging from a few hundred keV to several MeV. Here we apply this approach for lower energy (50–400 keV) gamma rays, using a handheld CdZnTe-based omnidirectional imaging system and an active coded mask imaging modality. We present our approach to real-time reconstruction using a scene-data-constrained graphics processing unit (GPU)-accelerated list-mode maximum likelihood expectation maximization (MLEM) algorithm and show results from several measurements in the lab and in the field.

The design of a catadioptric omnidirectional thermal imaging system based on the combination of genetic algorithm and gradient descent

This kind of panoramic system is difficult to design, the designers usually start from a commonly used patent and modify the patented structure, which is time consuming to make the structures to meet the requirements. In fact, the most critical part of the design is to determine the initial structure parameters of the quadrics mirror of this system instead of the parameters of the whole system, the remaining elements of the system could be integrated as a regular optical system. In this paper, we firstly created the error function about the aberrations of the quadrics mirror and calculated the minimum value of the error function related to the initial parameters of the quadrics mirror by combining the genetic algorithm (GA) with gradient descent (GD), after that we can obtain a group of parameters of the quadrics mirror. Finally, we completed the optical design of a catadioptric omnidirectional thermal imaging system based on the determined structure of the quadrics mirror. A system was obtained with an operating waveband of 8–12 μm, the field of view is: 360° in the horizontal direction, and 20–100° in the vertical direction; F/1.4; the resolution is 0.4@33lp/mm; the effective focal length is 5 mm. It demonstrates the reliability and validity of this method.

Omnidirectional Time-Lapse Imaging System for Egg-in-Cube Platform

Omnidirectional Time-Lapse Imaging System for Egg-in-Cube Platform

Camera self-calibration from projection silhouettes of an object in double planar mirrors.

In double planar mirror omnidirectional imaging systems, camera calibration is a crucial part of the 3D reconstruction process. Based on analysis of the imaging geometric features of double planar mirrors, three types of algorithms for the camera intrinsic parameters are presented by computing the imaged circular points and orthogonal vanishing points. The camera intrinsic parameters can be obtained by the constraints on the imaged circular points and the orthogonal vanishing points to the image of the absolute conic. Simulation, real data, and 3D reconstruction experiments are presented to show the feasibility and validity of the proposed methods.

Design and analysis of miniature high-resolution omnidirectional gaze optical imaging system

A miniature high-resolution omnidirectional gaze optical imaging system comprising one optical low-pass filter and 5 lens elements with just one aspheric surface was successfully designed. The total tracking length of the system is 14.7 mm and fit on a 5MPx 2/3in CCD with 2448 × 2050 pixel of 3.45 μm for the full 360° × 200° imaging. We introduced the difficulties in the design of ultrawide field of view system and proposed specific computations to overcome them by aberration theories, furthermore making a simulated analysis and performance evaluation using ZEMAX optical design software. The result shows that an admirable corrected field curvature along with a low F-theta distortion, and a perfect lateral and longitudinal color aberration correction were achieved; relative illumination of all field is over 68%; when the ambient temperature changes from −40 to 70 ℃, the modulation transfer function performs in a steady range at 75 lp/mm; all of these will promote the wide-field lens application in medical, automotive, and stereo vision.

遠隔監視システムを用いた災害地情報収集のための非等方性全方位視覚系(「VRにおける画像処理技術」特集)

遠隔監視システムを用いた災害地情報収集のための非等方性全方位視覚系(「VRにおける画像処理技術」特集)

恒等探测距离折反射式周视红外成像系统设计及分析

恒等探测距离折反射式周视红外成像系统设计及分析

Scene Depth Perception Based on Omnidirectional Structured Light.

A depth perception method combining omnidirectional images and encoding structured light was proposed. First, a new structured light pattern was presented by using monochromatic light. The primitive of the pattern consists of four-direction sand clock-like (FDSC) image. FDSC can provide more robust and accurate position compared with conventional pattern primitive. Second, on the basis of multiple reference planes, a calibration method of projector was proposed to significantly simplify projector calibration in the constructed omnidirectional imaging system. Third, a depth point cloud matching algorithm based on the principle of prior constraint iterative closest point under mobile condition was proposed to avoid the effect of occlusion. The experimental results demonstrated that the proposed method can acquire omnidirectional depth information about large-scale scenes. The error analysis of 16 groups of depth data reported a maximum measuring error of 0.53 mm and an average measuring error of 0.25 mm.

Optimal Spatial Resolution of Omnidirectional Imaging Systems for Pipe Inspection Applications

Achieving optimal spatial resolution in imaging systems plays a major role in the design of vision-based industrial inspection tools. Single-view omnidirectional imaging systems provide a cost-effective and computationally-traceable solution for real-time inspection of infrastructure with a favorable size factor. We formulate, for the first time, the spatial cylindrical resolution of omnidirectional Catadioptric and Dioptric imaging systems with the focus on pipe inspection applications. We also provide a design guideline to achieve the highest resolution in these systems. First, we deliver a comprehensive study on optimal resolution in Catadioptric imaging systems which consist of a perspective pinhole camera, a collimated laser as the light source, and a reflective surface (i.e., hyperbolic mirror). Variation of the spatial resolution in terms of the camera's focal length, the mirror curvature, and the relative position between the laser projector and the camera is fully investigated via simulation and experiments. Also, the optimal resolution in Dioptric systems, which consist of a camera with compound refractive lenses (i.e., fish-eye lens) is studied and compared with that in Catadioptric systems. Tests were conducted on a 40-cm-diameter PVC pipe in a controlled laboratory environment.

Improved wide-angle, fisheye and omnidirectional camera calibration

In this paper an improved method for calibrating wide-angle, fisheye and omnidirectional imaging systems is presented. We extend the calibration procedure proposed by Scaramuzza et al. by replacing the residual function and joint refinement of all parameters. In doing so, we achieve a more stable, robust and accurate calibration (up to factor 7) and can reduce the number of necessary calibration steps from five to three. After introducing the camera model and highlighting the differences from the current calibration procedure, we perform a comprehensive performance evaluation using several data sets and show the impact of the proposed calibration procedure on the calibration results.

Catadioptric 전방향 스테레오 영상시스템 및 3차원 좌표 복원

An image acquisition by using an optical mirror is called as a catadioptric method. The catadioptric imaging method is generally used for acquisition of 360-degree all directional visual information in an image. An exemplar omnidirectional optical mirror is the bowl-shaped hyperbolic mirror. In this paper, a single camera omnidirectional stereo imaging method is studied with an additional concave lens. It is possible to obtain 3 dimensional coordinates of environmental objects from the omnidirectional stereo image by matching the stereo image having different view points. The omnidirectional stereo imaging system in this paper is cost-effective and relatively easy for correspondence matching because of consistent camera intrinsic parameters in the stereo image. The parameters of the imaging system are extracted through 3-step calibration and the performance for 3-dimensional coordinates reconstruction is verified through experiments in this paper. Measurable range of the proposed imaging system is also presented by depth-resolution analysis.

Defocus deblurring for catadioptric omnidirectional imaging based on coded aperture and omni-total variation

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 coded aperture technique is proposed in this article. Firstly, the defocus blur of catadioptric omnidirectional imaging is analyzed to calculate the point spread function for different scene points. Then, a method of obtaining optimal focused plane is proposed. Lastly, based on the strategies of neighboring annuluses division and stitching of omnidirectional images, a deconvolution algorithm using omni-total variation prior is applied to obtain all-focused/sharp omnidirectional images. Experimental results demonstrate that the proposed method is effective for omnidirectional image defocus deblurring and can be applied to most existing catadioptric omnidirectional imaging systems.

HOPIS: hybrid omnidirectional and perspective imaging system for mobile robots.

In this paper, we present a framework for the hybrid omnidirectional and perspective robot vision system. Based on the hybrid imaging geometry, a generalized stereo approach is developed via the construction of virtual cameras. It is then used to rectify the hybrid image pair using the perspective projection model. The proposed method not only simplifies the computation of epipolar geometry for the hybrid imaging system, but also facilitates the stereo matching between the heterogeneous image formation. Experimental results for both the synthetic data and real scene images have demonstrated the feasibility of our approach.

Omni-total variation algorithm for the restoration of all-focused catadioptric image

In this paper, we present a novel omni-total variation (Omni-TV) algorithm for the restoration of defocus blur to obtain all-focused catadioptric image. Catadioptric omni-directional imaging systems usually consist of conventional cameras and curved mirrors for capturing 360° field of view. Mirror curvature in the catadioptric camera often leads to noticeable blurring artifacts in omni-directional imaging. The problem becomes more severe when high resolution sensor is introduced. In an omni-directional image, two points near each other may not be close to one another in the 3D scene. Traditional gradient computation cannot be directly applied to omni-directional image processing. Thus, an omni-gradient computing method combined with the characteristics of catadioptric imaging is proposed, in which an Omni-TV minimization is used as the constraint for deconvolution regularization. The proposed method is vital for improving catadioptric omni-directional imaging quality and promoting applications in related fields like omni-directional video and image processing.

Omnigradient Based Total Variation Minimization for Enhanced Defocus Deblurring of Omnidirectional Images

We propose a new method of image restoration for catadioptric defocus blur using omnitotal variation (Omni-TV) minimization based on omnigradient. Catadioptric omnidirectional imaging systems usually consist of conventional cameras and curved mirrors for capturing 360° field of view. 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 used. In an omnidirectional image, two points near each other may not be close to one another in the 3D scene. Traditional gradient computation cannot be directly applied to omnidirectional image processing. Thus, omnigradient computing method combined with the characteristics of catadioptric omnidirectional imaging is proposed. Following this Omni-TV minimization is used as the constraint for deconvolution regularization, leading to the restoration of defocus blur in an omnidirectional image to obtain all sharp omnidirectional images. The proposed method is important for improving catadioptric omnidirectional imaging quality and promoting applications in related fields like omnidirectional video and image processing.