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。     

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.     

Designing a mirror to realize a given projection

I present a design technique for realizing given projections as catadioptric sensors. In general, these problems do not have solutions, but approximate solutions may often be found that are visually acceptable. The method described reduces the problem to solving a linear system. A given transformation from the image plane to an object surface is shown to determine a vector field that is normal to the surface in the case where the vector field is a gradient. For the case when the vector field is not a gradient, several functionals are presented that may be minimized to give approximate solutions. As an application several new designs are described, including a mirror that directly gives a full 360-deg cylindrical projection without the need for any digital processing.     

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.     

Incorporating lens distortion into the design of undistorted catadioptric omnidirectional cameras

An improved approach for design of the catadioptric omnidirectional camera with horizontal scene undistorted imaging is described. In the proposed approach, the influence of the lens distortion on the imaging quality of the omnidirectional camera is taken into account. We establish a radial distortion model for an image pickup lens and retain some opposite distortion in the mirror to correct the distortion existing in the image pickup lens. A horizontal scene undistorted catadioptric omnidirectional camera is designed with an off-the-shelf TV short focus lens using our approach; the numerical simulation shows that the distortion introduced by the imaging lens is eliminated effectively.     

Motion and structure from line correspondences under orthographic projection

In this article we determine the multiplicity of solutions in several cases where line correspondences from orthographic projections over three views are known. We show that in the general case where the motion may vary between frames, seven line correspondences over three views are sufficient to guarantee that in general there is a unique solution for the rotation and directions of the lines, up to a reflection about a plane parallel to the camera plane. There is a three-parameter infinite family of solutions for the translations and depths of each line in this case. If the object is experiencing constant rotation, then four lines are sufficient to obtain solutions up to the same ambiguities. If the object is moving with constant rotation about a center of rotation which itself is moving in a straight line at constant velocity, then three lines are sufficient, and there is just a one-parameter infinite family of solutions for the translation and depths of the lines. Several examples are given to illustrate our results. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 301–312, 1997     

Realizing any central projection with a mirror pair

We show that, for any rotationally symmetric projection with a single virtual viewpoint, it is possible to design a two-mirror rotationally symmetric system that realizes the projection exactly. These mirror pairs are derived from two coupled differential equations. We give examples in which the projections from the sphere at infinity are stereographic, perspective, and equiresolution.     

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.     

High speed data collection system for magnetic field imaging by CTtechnique

A method of high-speed data collection used in imaging the magnetic-field distribution leaking from magnetic devices along any plane is proposed. The method uses the computed tomography (CT) technique. A high-speed data collection system developed for demonstrating the method is described. An image of the magnetic field is reconstructed from projection data provided by the voltage induced in the sensors of a line conductor and a rectangular coil moving in the plane of observation. Rotational scanning of the sensors is used for collecting the projections so that data-acquisition time can be reduced. To demonstrate the performance of the system, the reconstructed images of the magnetic-field distributions made by some permanent magnets are shown     

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.     

Sensitivity of optical sensors based on laser-excited surface-plasmon waves.

We investigate the effect of the divergence of a Gaussian laser beam on the resonance curve and the sensitivity of optical sensors based on surface-plasmon resonance (SPR). For He-Ne laser beams it is found that, for beams with a waist radius of less than 300 mum, the SPR-curve characteristics differ appreciably from the case in which a plane wave is considered. Simple expressions for the sensitivity of (bio)chemical sensors are given. A simple Lorentzian model is used to estimate the maximum possible sensitivity when a multilayer system is used to enhance the resonance peak. It was found that the sensitivity can reach its highest value when the width of the SPR curve is equal to the laser-beam divergence. The results could be particularly important when a SPR curve is used to measure the absolute value of the refractive index of a sample or the dielectric constant and the thickness of a metal layer.     

Analysis and application of multiframe superresolution processing for conventional imaging systems and lenslet arrays

Low-cost compact sensors for ultrasmall systems are a pressing need in many new applications. One potential solution is a shallow aspect ratio system using a lenslet array to form multiple undersampled subimages of a scene on a single focal plane array, where processing techniques then produce an upsampled restored image. We have investigated the optimization and theoretical limits of the performance of such arrays. We have built a hardware simulator and developed algorithms to process imagery similar to that of a full lenslet imaging sensor, which allowed us to quickly test optical components, algorithms, and complete system designs for future lenslet imaging systems.     

Iterative algorithm of phase determination in digital holography for real-time recording of real objects

We propose a numerical method to obtain complex amplitude distribution of a three-dimensional (3D) object from a digital hologram. The method consists of two processes. The first process is to measure simultaneously a hologram of the 3D object and an object intensity distribution by two image sensors. These intensity distributions give us the amplitude and absolute value of phase of the 3D object at the image sensor plane. The second process is the determination of phase distribution by a proposed iterative process based on the criterion that the reconstructed 3D object is in focus and its conjugate reconstruction is out of focus. Numerical and experimental results show the effectiveness of the proposed method.     

Suppression of excess noise in Transition-Edge Sensors using magnetic field and geometry

We report recent progress at NIST on Mo/Cu Transition-Edge Sensors (TESs). While the signal-band noise of our sensors agrees with theory, we observe excess high-frequency noise. We describe this noise and demonstrate that it can be strongly suppressed by a magnetic field perpendicular to the plane of the sensor. Both the excess noise and =(T/R)(dR/dT) depend strongly on field so our results show that accurate comparisons between devices are only possible when the field is well known or constant. We also present results showing the noise performance of TES designs incorporating parallel and perpendicular normal metal bars, an array of normal metal islands, and in wedge-shaped devices. We demonstrate significant reduction of high-frequency noise with the perpendicular bar devices at the cost of reduced . Both the bars and the magnetic field are useful noise reduction techniques for bolometers.     

Transformation of alternating magnetic and electric fields in a ferroelectric-conductor ring structure

We have studied a new phenomenon according to which an alternating magnetic field is transformed into electric voltage and vice versa in a structure comprising a ferroelectric ring with metal electrodes deposited onto its surface. The ferroelectric is polarized in the radial direction and placed into a constant magnetic field, which is perpendicular to the ring plane. The transformation results from a combination of the electromagnetic induction in the conducting circuit and the piezoelectric effect in the ferroelectric ring. This phenomenon can be used for creating magnetic sensors with linear characteristics.     

Optical Systems for Use at Low Light Levels

The development of image intensifier tubes and their application in instruments for operation under low light-level conditions created the need for optics which require specific properties. Recognition of the problems involved when combining a lens with a tube results in general requirements for the lens, some of which are different from those in standard lens design. Refined basic lens configurations and new systems have been introduced in this field, e.g. refractive and catadioptric lenses. Some examples of their performance are shown. In addition relay lenses having an extremely high speed have been realized for applications mainly for x-ray image intensifier systems. Single-tube instruments with a bi-ocular eyepiece are shown to have many advantages over the double-tube binocular.     

Optical modeling in Testbed Environment for Space Situational Awareness (TESSA)

We describe optical systems modeling in the Testbed Environment for Space Situational Awareness (TESSA) simulator. We begin by presenting a brief outline of the overall TESSA architecture and focus on components for modeling optical sensors. Both image generation and image processing stages are described in detail, highlighting the differences in modeling ground- and space-based sensors. We conclude by outlining the applicability domains for the TESSA simulator, including potential real-life scenarios.     

An original approach to eddy current problems through a complexelectrical image concept

In this paper, we propose an original method for the physical analysis of electromagnetic interactions between an inductive sensor and any homogeneous conducting plane target. In the first part of this paper, the basic principles of inductive sensors are recalled. Then, we solve Maxwell's equations in order to obtain an analytical model for the relationship between the target properties and the electrical signals for a U-shaped sensor. Next, we emphasize the fact that our analytical relations can be interpreted as an extension of the electrical image method, even in the most difficult case of conducting and magnetic targets. In the last part, we present some measurements illustrating this new electrical image concept     

实体模型图纸化转换中复合剖的实现方法

提出了通过建立浮动模块的方法，解决了实体模型提取正投影图时AutoCAD系统只能定义单一剖切面而不能定义多个剖切面的问题。笔者列举了提取模型复合剖视图时的各种问题，提出了浮动模块的概念。指出了它的作用、形式及特点，并通过实例说明如何利用浮动模块来构建和变换实体模型的结构与位置，以使复合剖切面单一化和剖切过程简单化。最后结合实例对创建浮动模块的方法和提取复合剖视图的过程作了详细说明。     

All-spherical catadioptric telescope design for wide-field imaging

The current trend in building medium-size telescopes for wide-field imaging is to use a Ritchey-Chrétien (RC) design with a multilens corrector near the focus. Our goal is to find a cost-effective alternative design to the RC system for seeing-limited observations. We present an f/4.5 all-spherical catadioptric system with a 1.5° field of view. The system consists of a 0.8 m spherical primary and 0.4 m flat secondary mirror combined with a meniscus lens and followed by a three-lens field corrector. The optical performance is comparable to an equivalent f/4.5 RC system. We conclude that, for telescopes with apertures up to 2 m, the catadioptric design is a good alternative to the RC system.