暗通道与交叉通道多先验联合多光谱超分辨率算法

针对多光谱遥感图像超分辨率重建易受噪声和色差影响的问题,提出了暗通道与交叉通道多先验联合的多光谱超分辨率算法。首先,在传统全变分先验的基础上,引入了暗通道先验与交叉通道先验。然后,基于最大后验概率估计理论,建立了多先验联合的多光谱超分辨率重建算法。所提算法可实现图像边缘信息恢复、图像纹理信息恢复、噪声抑制、阶梯效应抑制和色差抑制,进而综合提升了重建图像的质量。最后,开展了实验验证,结果表明,在不同信噪比(10～40 dB)和色差干扰下,相比已有算法,所提算法的重建效果显著提升。     

基于分色校正的大像差光学成像系统图像处理技术

为解决传统大视场高分辨相机光学系统复杂、成本高昂等问题,利用同心多尺度计算成像系统,通过图像处理方式校正简化的光学结构残留的球差和倍率色差.分析光学系统的像差特性,得到不同波长的成像数据,并根据系统参量和像差表现,用红、绿、蓝三通道分别校正方案对图像进行处理.首先采用非线性图像缩放法,统一不同色光的放大倍率,完成倍率色差的校正;然后针对光学系统的点扩散函数随空间位置变化的特性,对各通道模糊图像进行分块,用Lucy-Richardson算法对每一个图像块进行图像复原,完成单色像差校正;最后融合三通道获得校正图像.用均方误差、峰值信噪比和结构相似度等方法进行图像质量评价,结果表明本文方法能够有效校正计算成像系统中的残留像差,提升图像质量.     

大视场高像质简单光学系统的光学-算法协同设计

为了实现高像质相机低成本、小型化的需求,本文提出了一种大视场简单光学系统的光学-算法协同设计方法,并通过图像复原算法校正简单光学系统的残余像差。首先,针对大视场光学系统,对空间变化的交叉通道去卷积算法进行改进,加入倍率色差校正,使图像复原算法可显著去除色差的影响。然后,在光学设计过程中,放开色差的约束,并专注优化绿色通道的像质,使其成像锐利,在后期交叉通道去卷积算法中有助于红、蓝两通道图像复原。利用该方法设计了一个由两片同种材料的镜片构成的大视场简单光学系统。系统焦距为50 mm,全视场为46°,F数为5. 6,探测器分辨率为1 000万像素。实验结果表明:本文设计的两片镜、大视场简单光学系统的成像质量可媲美三片式库克镜头,明显优于纯图像复原的结果。本文方法实现了大视场简单光学系统的设计,并能够通过系统最终获得高分辨率、高像质图像。     

基于加权暗通道的图像去雾方法

传统基于暗通道图像去雾中仅考虑初始透射图对于透射图优化的影响,而未充分考虑深度信息对于透射图优化贡献不同的特点,造成去雾结果在深度不连续处出现"晕"且离视点较远区域的去雾效果有明显下降.针对上述问题,本文提出一种基于边缘特征的加权暗通道先验去雾算法.该方法根据边缘特征的位置估计深度信息的连续性,将边缘点及非边缘点赋予不同权值,对加权透射图优化求解.仿真实验表明,新的去雾算法在恢复图像细节的基础上能够有效抑制"晕"的产生,证实了本文方法的可行性和有效性.     

基于像差选择性校正的光学-数字联合设计

提出面向成像系统的光学和数字图像处理联合优化设计.根据泽尼克多项式模型分析了每种像差对成像清晰度的影响;在变分贝叶斯框架下,提出了基于加权双向差分先验模型的像差数字校正算法;将像差分为易于数字校正和不易于数字校正两类,建立基于像差选择性校正策略的光学-数字处理联合设计方法.采用联合设计方法设计了三镜片大像差光学系统,其奈奎斯特频率处的MTF值约为0.50,采用传统方法设计的六镜片光学系统MTF值约为0.53,两系统成像质量相当,本文方法可降低系统复杂度.     

多尺度窗口的自适应透射率修复交通图像去雾方法

基于传统暗原色先验原理的图像去雾算法存在的"halo"效应,且图像中明亮区域存在颜色失真现象,针对此问题,本文提出了多尺度窗口的自适应透射率修复交通图像去雾方法。首先,利用新的8方向边缘检测算子求取图像中景深突变区域,根据暗通道先验理论和前一步求得的景深突变区域,在景深变化较大区域使用5×5的窗口,景深变化较小区域则使用15×15的窗口得到暗原色估计图。同时,针对暗通道先验原理对近景部分存在白色区域时透射率估计不准确的问题,引入了自适应透射率修复方法,通过引导滤波器得到边缘增强后的暗原色图像,并利用其与原暗原色图像的纹理差对近景区域的透射率进行修正,完成图像去雾。实验结果表明:双边滤波和梯度双边滤波两种算法均存在halo现象,并且在包含白色物体的明亮区域色彩失真严重,客观评价指标失去意义;相比于引导滤波,本文去雾算法的各项指标均有所提高,其中平均梯度平均提高了8. 305%,PSNR平均提高了12. 455%,边缘强度因子平均提高了7. 77%。本文算法有效解决了复原图像中"halo"效应现象和明亮区域颜色失真现象,去雾效果最优。     

基于改进暗原色先验和颜色校正的水下图像增强

水下图像成像过程与雾天图像类似,但传统的去雾方法用于水下图像处理效果欠佳。针对水下捕获图像存在颜色衰减严重和蓝(绿)色基调的问题,提出了一种基于改进暗原色先验和颜色校正的水下图像增强方法。结合光在水下的传播特性,对空气中的暗原色先验去雾算法进行改进,在求取水下暗原色通道和图像背景光时考虑红色通道的逆通道;提出先采用改进的水下暗原色先验法去除后向散射光,再通过白平衡算法对增强后的水下图像进行颜色校正的方法。实验结果表明,相比于传统算法,本文的方法在处理后向散射严重的水下图像时,可以获得更高的清晰度和对比度。     

基于双透射率水下成像模型的图像颜色校正

针对水下图像颜色失真的问题,提出了基于双透射率水下成像模型的图像颜色校正算法。在水下成像模型的基础上,将透射率定义为直接分量透射率和后向散射分量透射率;通过红色暗通道先验获得后向散射分量透射率,并精确估计背景光,利用无退化像素点获得三通道的直接分量透射率;最后将两个透射率代入成像模型获得复原图像。实验结果表明,该算法仅依靠物理模型便能有效地去除水下图像的色偏。     

基于结构先验的加权NLTV能谱CT重建算法

能谱计算机断层扫描在数据采集过程中可以区分光子能量,并同时得到多个能量通道的投影。由于单个能量通道只包含了总光子数的一小部分,且大多数光子计数探测器只能承受有限的计数率,所以多通道投影通常含有较大的噪声。为了从噪声投影中重建出高质量的能谱图像,利用不同能量通道下重建图像具有结构相似性,提出一种基于结构先验的加权非局部全变分(NLTV)重建算法。设计了简单和复杂两种模型进行仿真,比较了TV算法、NLTV算法、加权NLTV算法,以及基于结构先验的加权NLTV等去噪算法的重建效果,结果表明,本文算法对复杂模型和高噪声模型的重建具有明显优势。     

闭环控制自适应光学系统变形镜约束技术的研究

为了实现闭环控制自适应光学(AO)系统中的变形镜对倾斜及平移像差的约束,分析了基于限定向量算法对系统动态特性及校正残差的影响,数值仿真结果表明,限定向量算法无法实现约束量的完全抑制,并且严重影响系统的校正效果。提出了基于投影抑制的算法,通过分离像差及在控制电压上实现对变形镜的抑制,采用2种算法利用单变形镜对含有倾斜的像差进行校正的仿真结果表明,采用限定向量算法,变形镜产生了使远场偏移9.3 pixel的整体倾斜时,基于向量投影抑制算法只产生小于0.02 pixel的偏移,并且对前36阶各单阶泽尼克模式的像差校正后具有更高的斯特列尔比。结果表明,基于投影抑制的算法具有更好的约束能力、更低的条件数及具有更优的校正效果。     

Studies of transverse chromatic aberration based on individual eye model

Two kinds of individual eye models, with and without involving the angle between visual axis and optical axis, are constructed according to the measurements of the corneal surfaces, the optical axis lengths and wavefront aberrations. The constructed eye models are then used to investigate the properties of the transverse chromatic aberration (TCA) and its influence on visual performance. The statistical distributions of the horizontal TCA, vertical TCA and the absolute magnitude of the TCA over the spectrum from 470 to 650 nm are provided, respectively. The variations of TCA with wavelength as referring to the central wavelength of 555 nm for five subjects are also provided. Then we evaluate the impact of TCA on image performance in comparison with longitudinal chromatic aberration (LCA). It is shown that LCA is more detrimental than foveal TCA in image quality. It is found that, while LCA was corrected well, the foveal TCA is simultaneously corrected. Finally, we investigate the correction of peripheral TCA with an achromatizing element. The correction of peripheral TCA of human eye strongly depends on the location of the achromatizing element, and with the element in front of the eye, the peripheral TCA cannot be corrected.     

The study of correction for chromatic aberrations of human eye with diffractive–refractive hybrid elements

A chromatic corrector with two refractive–diffractive hybrid elements is designed over a reasonable wide field-of-view of 7° to correct the chromatic aberrations of human eye. We investigate the performance of the corrector using several optical criteria in a comparison with the chromatic corrector with single refractive–diffractive element. Both the correctors can correct the longitudinal chromatic aberration (LCA) fairly. It is demonstrated that the chromatic corrector with single element introduces serious eccentric transverse chromatic aberration (TCA), which deteriorates the image quality at the edge field-of-view. On using the chromatic corrector with two refractive–diffractive elements, not only the LCA but also the TCA can be corrected very well. The designed chromatic corrector can be used to improve the retinal image quality and has potential application in the design of visual instruments.     

色散效应对聚光多结太阳电池性能的影响及优化

针对色散效应导致聚光多结太阳电池性能降低的问题,使用分布式三维等效电路模型计算高倍聚光下GaInP/GaInAs/Ge三结太阳电池的输出特性,通过分析电池各层的电压分布、暗电流分布以及横向电流分布,研究了不同电池尺寸下色散效应对电池性能影响的机理.结果表明:色散使多结太阳电池在局部区域的光生电流变得不匹配,随着电池尺寸的减小,局部区域之间失配的光生电流能够以横向电流的形式相互补偿,使电池整体的电流更加匹配,从而减小色散效应的影响.当电池芯片尺寸较大(20 mm×20 mm)时,色散主要降低电池的短路电流密度,色散光斑下电池的效率仅相当于无色散时的94%;当电池芯片尺寸减小到2 mm×2 mm时,短路电流密度与无色散时相等,但横向电阻降低了电池的填充因子.当电池芯片尺寸进一步减小到0.4 mm×0.4 mm时,色散与无色散光斑下电池的各项性能几乎没有差别,效率均约为34.5%,色散效应的影响可忽略不计.     

一种基于共轭节面的图像畸变分析方法

无像差的光学相机的成像模型可由其共轭节面模型等效表示。针孔模型本身忽略了偏离该等效模型的误差,也无法表示平板玻璃的平移误差、光轴的安装误差以及实际相机光学系统的像差,这四个因素都会引起图像畸变。基于此利用共轭节面的性质建立了一种图像畸变几何模型,并与广泛采用的像差模型进行了对比,从理论上解释了像差模型各个系数的物理意义。对某实际针孔相机进行仿真分析,该几何模型给出的相对径向畸变、角度误差在设计参数的范围以内,并且可以模拟图像的非对称畸变。该几何模型需要辨识包含主面相关参数、光轴倾斜角和平板玻璃的轴向球差在内的4个参数,辨识参数较少,理论上可以作为一种新的图像畸变校正方法。     

Design of Plane-Symmetric Low <Emphasis Type="Italic">F</Emphasis>-number Reflective System Based on Perturbation Aberration Model

All-reflective optical systems have theoretically no chromatic aberration and are suitable for wide spectral application, but co-axial reflective systems are difficult to design as low F-number optical systems. In this paper, the aberration of plane-symmetric optical systems with low F-number is analyzed based on the wavefront derived from optical path length. Up to third-order aberrations are classified into three categories by their characteristics. The reduction method of the dominant aberration, astigmatism-like aberration, is proposed. In the method, the Gauss image plane is modeled by means of a simplified mirror surface with third-order approximation. Because the system is plane-symmetric, symmetric cross section and asymmetric cross section are modelled differently. The design example of a three-mirror system with F/2 is shown.     

泛卡塞格林光学系统的色差研究

泛卡塞格林光学系统结构简单、像质优良,广泛应用于空间光学领域中。从对研制完成的谱段位于500～800nm的泛卡塞格林光学镜头的调制传递函数(MTF)的测量结果出发,结合泛卡塞格林光学系统的结构特点,分析表明光学设计的色差来源于其高次施密特非球面镜,提出了一种利用非球面镜的最小色差条件来改进光学系统的新方法。通过三级像差理论,分析了施密特非球面镜的面形方程,计算出最小色差条件及相应的中性带高度,进行光学设计的优化改进,取得了良好的效果。结果表明,改进后光学系统的色差由原来的31.4μm减少为4.25μm,且光学系统的MTF值达到0.6以上(40lp/mm),像质优良。该方法为类似光学系统的设计提供了一定的参考价值。     

Differential algebraic method for arbitrary-order chromatic aberration analysis of electrostatic lenses

In this paper, differential algebra is applied to calculate arbitrary high-order chromatic aberrations of electrostatic electron lenses. Expressions of differential algebraic form of high-order combined chromatic aberration coefficients are obtained and arbitrary-order chromatic aberrations can be calculated numerically. As an example, a typical Schiske's electrostatic lens has been studied. All the first- to third-order chromatic aberration coefficients of the lens have been calculated, and the pattern of the first-order chromatic aberration has been given as well.     

梯度折射率棒透镜的色差估计

对梯度折射率(GRIN)棒透镜色差的影响因素进行了研究,在玻璃光学性质计算模型的基础上建立了梯度折射率棒透镜色差估计函数与基础玻璃性能、交换离子对性质和参与交换的离子数量之间的关系。对Na+/Li+,K+/Cs+和K+/Tl+交换制备的梯度折射率棒透镜的色差进行了计算,结果表明,GRIN棒透镜的色差评价函数主要取决于基础玻璃和交换离子的性质,而与参与交换的离子数量无关。     

梯度折射率棒透镜的色差模型

本文提出一个梯度折射率棒透镜(GRIN－RodLens)的色差模型,并运用本模型合理地解释了在色差测量过程发现的各类色差现象.     

Theory of paraxial lateral aberrations of electrostatic imaging electrostatic electron optics based on asymptotic solutions and its verification

In imaging electron optics, study of geometrical lateral aberrations of third order and paraxial lateral aberrations of second order has traditionally been paid more attention to, but the existence of paraxial chromatic aberrations of third order and paraxial chromatic aberrations of magnification of third order was almost ignored, and the general form of paraxial lateral aberration has not been studied theoretically.In the present paper, the paraxial lateral aberrations expressed in general form have been derived emphatically on the basis of asymptotic solutions of paraxial equation. The relationship between the coefficients of asymptotic solutions has been investigated, which proves that the coefficients of asymptotic solutions are related each other. Through a bi-electrode electrostatic spherical concentric system model, two special solutions expressed by asymptotic solutions and accurate solutions in a bi-electrode electrostatic spherical concentric system have been deduced, and the paraxial lateral aberrations have been verified and tested, in which the aberration coefficients are solved by asymptotic solutions of paraxial equation. Result completely proves that the approach based on asymptotic solutions to solve the paraxial lateral aberrations are practicable and accurate enough. The paraxial chromatic aberration of magnification of third order and the paraxial chromatic aberration of third order have been firstly derived, and the Recknagel-Artimovich formula of paraxial chromatic aberration of second order which possess an greatest part in the whole paraxial lateral aberrations has been deduced and confirmed. A simple and clear form for expressing paraxial lateral aberrations of imaging electron optics is suggested for practical use. Results of the present paper will have theoretical value for aberration theory of imaging electron optics and practical significance for the design of image tubes.