CMOS APS图像传感器的像质分析

使用标准CMOS制作工艺生产的有源像素传感器（APS）引起了广泛关注。为了确定CMOS APS成像系统设计的主要参数选择的正确性,以及能否满足要求或指标,需要对相机系统的像质进行分析。考虑到CMOS APS图像传感器与CCD的不同,在分析时计算了CMOS APS成像系统中的镜头、滤光片和焦平面的调制传递函数（MTF）,系统MTF曲线为各个部分MTF值之积。在系统截止频率范围内,利用MTF曲线所围面积的大小来评价系统的成像质量。在系统制造之前,用调制传递函数作为像质的评价方法,看其是否符合使用要求,是十分有价值的工作。     

两种排列方式光纤传像束的像质评价

根据调制传递函数对比度定义,推导了线列光纤传像束调制传递函数(MTF)的数理关系,建立了光纤直径有随机误差的线列光纤传像束MTF仿真模型,对MTF进行数值分析。通过考虑在光纤传像束中输入信号与光纤的位相匹配对MTF的影响,分析了V型槽排列和紧密排列两种不同方式的光纤传像束的平均MTF。结果显示,有随机误差的光纤束的平均MTF值分别分布于理想传像束平均MTF曲线附近,表明了光纤自身的误差对传像束的平均MTF影响不大;V型槽排列的线列光纤束的像质优于紧密排列方式的线列光纤束。     

高级像差对人眼成像质量和视觉的影响

定量地研究高级像差对人眼成像质量和视觉的影响对人眼像差矫正具有重要的实验和临床意义.利用Hartmann-Shack波前传感器人眼像差仪测量了正常人眼6mm瞳孔的波前像差,由波前像差计算出人眼光学系统的光学调制传递函数MTF和Strehl比率,并由MTF和视网膜空间像调制度AIM曲线计算出人眼视锐度和对比敏感度函数CSF.根据MTF和Strehl比率分析了高级像差对人眼成像质量的影响,根据视锐度和对比敏感度函数CSF分析了高级波像差对视觉的影响.研究表明Zernik前6级像差对人眼成像质量和视觉的影响是不可忽略的,更高级的像差对人眼成像质量和视觉的影响较小,甚至可以忽略.对Zemik前6级像差进行矫正,可以得到相当好的视觉.     

亚像元成像系统B样条插值方法

亚像元动态成像技术是实现遥感器高分辨、小型化非常有效的方法。将B样条插值方法应用于亚像元动态成像,提出利用四条B样条曲线插值两幅亚像元图像的方法。该方法利用待插值点邻域范围内的十二个点做四条B样条曲线,并取其中点的算术平均值作为待插值点的像素值。利用文中推导的插值算式可方便地计算待插值点的像素值。通过仿真对提出的方法进行了验证,给出了该方法与其它几种常用插值方法的性能比较,分析结果表明,该方法较其它几种方法得到的高分辨率图像效果更佳。     

人眼不同瞳孔直径波前像差特性分析

采用Hartmann-Shack人眼像差仪,测量了人眼在3.1mm,5.2mm和6mm瞳孔直径下的波前像差。波前像差的RMS值表明,随着瞳孔直径的增大,人眼各阶波前像差均随着增大。与瞳孔直径为3.1mm时相比,瞳孔直径为6mm和5.2mm时,Zernike2-10阶波前像差的RMS值分别增大1.2-7.7倍和1.1-4.8倍。用调制传递函数(MTF)和Strehl比评价了高阶波前像差对成像质量的影响,结果表明,大瞳孔高阶波前像差对成像质量的影响大于小瞳孔;在3.1mm,5.2mm和6mm瞳孔直径下,欲达到衍射极限的Strehl比率,分别需要矫正Zernike波前像差前2-4阶、前3-6阶和前5-7阶,需矫正的像差阶数随瞳孔直径的增大而增加。     

基于像元分解的亚像元级遥感数据分类精度评估方法

为减小混合像元现象给遥感数据分类精度评估过程带来的影响,将像元分解技术引入到分类精度评估中,提出了基于像元分解的亚像元级分类精度评估方法,并给出了相应的处理流程及精度评估所需误差矩阵的计算方法.实验结果表明,亚像元级分类精度评估方法能够体现混合像元在分类精度评估过程中的影响,能够从一定程度上细化各分类算法的优劣,降低由于空间分辨率所引起的分类精度评估结果的不确定性.     

像移和采样共同作用下的TDICCD探测器像质

CCD探测器的像元尺寸一般来说是光学系统弥散斑的几倍,因此以CCD探测器为接收器的光学成像系统在理论上可以近似看作是空间移不变系统。采用计算机仿真的方法来研究在空间移变条件下的TDICCD遥感相机的影像分辨力和像质问题,结果是：在目标条带宽度一定时,像元尺寸为a,像移量为a/3,a/2,a,MTF分别下降为0．918,0．876,0．753;当MTF基本相等时,像移量为a/3,a/2,a,条带宽度为36,38,44。通过模拟,认识到在像移大于a/3时,Angle=0和Angle≠0的肘阡相差小于1％;并在像移量大于a/3的条件下得到了适用于工程应用的像元尺寸、像移量、分辨力、MTF的一个简洁函数。     

数字图像单个像元分形维数的特征与计算方法

通过分形理论把空间结构信息引入遥感分类中,必须解决分形维数计算的问题,为此提出了一种通过相邻像元间灰度值大小的变化计算数字图像单个像元分形维数的算法。选定计算窗口值 L 后,运用所编程序对 TM 遥感数据进行运算,并得到所需分维值数据。发现所得分维值随窗口值 L 增大而减小;大窗口值的分维值图像较抽象,但建议窗口值不超过 61;小窗口值的分维值图像较清晰,但窗口值不能小于 5。     

连续扫描成像光学系统MTF的数值分析(英文)

为了实现高分辨力,在地球静止轨道上工作的遥感系统通常装备大口径光学系统,但光学系统的视场通常很小。扫描成像技术可使地球静止轨道上的高分辨力遥感光学系统获得更大的观测范围。但在扫描镜转动时像点一直在移动,所以在CCD曝光时间内会出现像点混叠。因此,扫描成像光学系统的调制传递函数将变差。本文采用动态光学传递函数分析方法研究了连续扫描成像光学系统成像性能。结果表明,在曝光时间范围0.5~1.5 ms,扫描镜的旋转角度应小于(7×10-6)o以保持较高的MTF。最后,给出了连续扫描镜的驱动方法并分析了扫描镜驱动不稳定性对MTF的影响。本文的研究结果可为连续扫描成像光学系统的深入研究和制作提供参考。     

采用针孔像分析法的OTF测试

开发了基于针孔像分析法的视频光学传递函数测试装置。测试装置采用 CCD 为像接收器件,通过针孔像分析,一次获得光学系统的二维传递函数。根据频谱分析理论,结合物频谱校正和空间频率对应等因素,研究了测试组件,包括针孔直径、准直物镜焦距、CCD 像元尺寸和显微物镜放大倍数等参数设置对空间频率对应及测试精度的影响;采用胖零设置和多幅图像平均法降低噪音影响,根据各组件自身的传递函数修正其对测试精度的影响。50mm 标准透镜的比对实验结果表明,采用本装置和本文建立的数据处理、误差校正方法,调制传递函数测试精度为±3%。     

近贴X射线成像系统调制传递特性联合检测方法

利用光学调制传递函数评价原理,在建立了各个成像子系统信号传递关系的基础上,提出了一种近贴式X射线成像光学调制传递特性检测方法。从像增强器约束、射线源约束和噪声约束这3个角度对近贴式X射线成像系统光学调制传递函数进行理论定标。将近贴式X射线成像系统后端的CCD望远系统换成CCD显微系统并对不同空间分辨率的铅栅进行成像与对比度拟合。实验结果表明:时域均衡可以有效提高拟合精度。其拟合结果表明空间分辨率为10线对/mm时其调制传递函数仍有10%,与理论定标结果基本一致。故传统近贴式X射线成像系统的望远光学镜头分辨率才是真正的成像瓶颈。     

Partially light-controlled imager based on liquid crystal plate and image intensifier for aurora and airglow measurement

In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 10(4)-10(-2) lx, the corresponding electron count is 1.57×10(5) - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2×10(5) lx. The clear details of [symbols: see text] presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement.     

Quantitative characterization of the limiting resolution of a microscanning imager

A method to determine the limiting resolution of a microscanning imager is proposed. Specifically, both the sample-scene phase effects and aliasing effects due to microscanning are modeled in this method by combining the pixel transfer function and the squeeze modulation transfer function. Further, this model is used to calculate the amount of improvement from typical microscanning modes to the limiting resolution of the imager focusing on various blur factors. Analytical results show that the limiting resolution of the microscanning imager is closely related to microscanning modes. The amount of improvement from different microscanning modes to the limiting resolution is different and is closely associated with the fill factor and the blur factors. The conclusion obtained will be helpful in choosing the optimum microscanning mode according to the fill factor of the detector and system blur factors.     

Improving photon count and flat profiles of multiplex imaging systems with the odd-symmetric quadratic phase modulation mask

The odd-symmetric quadratic (OSQ) phase mask is examined as a candidate for reduction of working distance and enhancement of light collection in multiplex imaging systems. The knowledge gained from the exact mathematical representation of the optical transfer function of the OSQ phase mask imager is exploited to explain the limits of system performance and quantify the upper bound on the magnitude of defocus within which this wavefront coding imager can successfully operate. The sensitivity of this imaging system to defocus about the special imaging condition that yields an enhanced dynamic range is examined, and it is shown that the modulation transfer function (MTF) degradation when the magnitude of misfocus is increased past this condition is much more gradual than the degradation of a conventional imager past a zero-misfocus state. The condition required for the spatial frequency and angular resolution of this OSQ phase mask imager to exceed that of its counterpart scaled imager is established, and results of simulated imaging under a reduced working distance configuration are presented.     

Applications of the phase transfer function of digital incoherent imaging systems

The phase of the optical transfer function is advocated as an important tool in the characterization of modern incoherent imaging systems. It is shown that knowledge of the phase transfer function (PTF) can benefit a diverse array of applications involving both traditional and computational imaging systems. Areas of potential benefits are discussed, and three applications are presented, demonstrating the utility of the phase of the complex frequency response in practical scenarios. In traditional imaging systems, the PTF is shown via simulation results to be strongly coupled with odd-order aberrations and hence useful in misalignment detection and correction. In computational imaging systems, experimental results confirm that the PTF can be successfully applied to subpixel shift estimation and wavefront coding characterization tasks.     

Theoretical approach to CMOS APS PSF and MTF modeling - evaluation

In this work, a fully theoretical CMOS active pixel sensor (APS) modulation transfer function model is formulated, evaluated, and compared with practical results. The model is based on a two-dimensional diffusion equation solution and covers the symmetrical photocarriers diffusion effect together with the impact of the pixel active area geometrical shape. Thorough scanning results obtained by means of a unique submicron scanning system (the S-cube system) from various APS chips, implemented in a standard CMOS 0.35-/spl mu/m technology, are compared with our theoretical predictions. The agreement of the presented comparison results indicates that for any potential active area shape, an analytical reliable estimate of image performance is possible.     

Modulation Transfer Function Assessment for Sampled Imaging Systems: A Generalization of the Line Spread Function

Abstract

The line spread function is a classical figure of merit for the modulation transfer function assessment of an optical system. However, this test cannot be directly applied to sampled imaging systems as they often exhibit aliasing effects. The purpose of this paper is to define a new figure of merit which allows the characterization of the transfer of all spatial frequencies even those which are placed after the Nyquist frequency. An experiment has been carried out to demonstrate the effectiveness of this new test.     

Adaptive flat multiresolution multiplexed computational imaging architecture utilizing micromirror arrays to steer subimager fields of view

A thin, agile multiresolution, computational imaging sensor architecture, termed PANOPTES (processing arrays of Nyguist-limited observations to produce a thin electro-optic sensor), which utilizes arrays of microelectromechanical mirrors to adaptively redirect the fields of view of multiple low-resolution subimagers, is described. An information theory-based algorithm adapts the system and restores the image. The modulation transfer function (MTF) effects of utilizing micromirror arrays to steering imaging systems are analyzed, and computational methods for combining data collected from systems with differing MTFs are presented.     

Dealiased spectral images from aliased Fizeau Fourier transform spectroscopy measurements

Fizeau Fourier transform imaging spectroscopy (FTIS) is a technique for collecting both spatial and spectral information about an object with a Fizeau imaging interferometer and postprocessing. The technique possesses unconventional imaging properties due to the fact that the system transfer functions, including the imaging and spectral postprocessing operations, are given by cross correlations between subapertures of the optical system, in comparison with the conventional optical transfer function, which is given by the autocorrelation of the entire aperture of the system. The unconventional imaging properties of Fizeau FTIS can be exploited to form spatially dealiased spectral images from undersampled intensity measurements (obtain superresolution relative to the detector pixel spacing). We demonstrate this dealiasing technique through computer simulations and discuss the associated design and operational trade-offs.     

Effect of spatial coherence on knife-edge measurements of detector modulation transfer function

When an image of an edge object is used in the determination of the modulation transfer function of a detector array, the partial coherence of the illumination is often ignored. Although this approximation is valid in some cases, it may not be satisfactory, particularly for the small detector elements characteristic of present-day charge-coupled devices. Here we demonstrate the effect of partial coherence on edge-based modulation transfer function determination for various pixel sizes, degrees of coherence, and f-numbers of the test optics.