虹膜区域选取与识别率对应关系分析

在人眼自然张开状态下,虹膜遭受睫毛、眼睑和反射光斑不同程度地干扰而失去了部分信息,因此需要找出虹膜保留面积与虹膜识别率之间的对应关系,从而根据小同的识别率要求估计不同的人眼最小张开程度.利用相关系数识别方法作为评测手段分别在不同的虹膜图库中进行了实验.结果证明,选取靠近瞳孔的虹膜内环区域与整个虹膜区域的比率在大于37.5%时,或者暴露的虹膜两侧扇形的角度大于70.时,就可以获得区分个体的特征量,达到比较稳定的识别率.实验结果还给出了虹膜内环区域而积与识别率的对应关系曲线以及虹膜两侧扇形区域面积与识别率之间的对应关系曲线.     

一种新颖的虹膜轮廓提取方法

传统的虹膜定位方法是在人眼图像上把虹膜轮廓当作理想圆来提取.针对虹膜内边界不是理想圆,外边界边缘模糊等问题,提出一种新的虹膜轮廓提取方法.先利用极坐标变换将包含全部虹膜区域的某个范围展开成矩形形状,然后在此矩形区域上根据灰度的阶跃进行虹膜真实内边界的查找,最后在矩形区域上利用直线定位虹膜外边界代替在人眼图像上利用圆定位外边界.该方法不仅解决了内边界不是理想圆造成的瞳孔遗留或纹理损失问题,而且以点、线检测代替圆检测显著降低了虹膜定位时间.通过对CASIA-IrisV3虹膜图像库进行定位测试结果表明,该方法平均定位时间0.172 s,定位准确率99.35%.     

原向反射屏剩余发散角测试

 提出了玻璃微珠原向反射屏的剩余发散角概念和测试方法：将激光光束投射到原向反射屏,其反射回的激光光束成像到硫酸纸（接收屏）上。利用相机拍摄不同距离下原向反射屏的成像光斑,得到光斑的图像数据;并处理相应图像数据,计算出剩余发散角。通过实验测得所用的玻璃微珠原向反射屏的剩余发散角为0.447 8°。     

基于单位扇环灰度的虹膜定位算法

提出了基于单位扇环灰度的虹膜定位算法。利用投影法分割出一个包含瞳孔的矩形区域,通过最大类间方差法确定该矩形区域的阈值,完成瞳孔的分割。对于虹膜外边界的定位,需要基于瞳孔中心分割出某一方向上的扇形区域,以5个像素作为扇形区域的步长,计算每个扇环的平均灰度值,根据灰度变化情况就可以确定该方向上的虹膜外边界点。其他方向上的边界点也通过此方法确定。对这些边界点进行筛选并进行圆的拟合,最终实现虹膜的定位。实验结果表明,采用该方法所分割的虹膜图像可以获得良好的效果,具有良好的应用和参考价值。     

新型离轴反射变焦距光学系统的多视场检测方法

基于对离轴反射变焦距光学系统进行计算机辅助装调研究, 需要检测离轴反射变焦距系统各个视场的波像差, 除零度视场外, 获得包括其他视场的波像差有助于提高计算机辅助装调的准确性, 但是目前已有的波像差检测方法往往只能获得系统零度视场的波像差. 本文针对这个难题提出了一种检测离轴反射变焦距光学系统各个视场波像差的方法, 并应用于离轴三反变焦距光学系统的各视场波像差仿真检测. 该方法在传统自准直干涉法的基础上进行改进, 关键在于采用变形镜代替扫描的平面镜, 并采用夏克-哈特曼波前传感器代替干涉仪, 配合精确标定的激光器光源阵列, 可以实现对离轴三反变焦距光学系统的多视场波像差同时检测. 由理论分析和仿真模拟得出, 该系统在视场(0°, 3°), (0°, 4.2°), (0°, 5.5°), (0°, 7°), (0°, 9.8°), (0°, 14°)处经过变形镜补偿后的剩余波像差的RMS值分别为0.00039λ, 0.00075λ, 0.0024λ, 0.00017λ, 0.00053λ, 0.0057λ, 分析仿真结果表明此检测方案是可行的, 且适用于离轴反射变焦距系统的计算机辅助装调技术的研究.     

利用双反射镜控制实现无线光通信光束对准

针对远距离无线光通信中光束跟踪受长距离大气传输不确定因素影响大的问题,提出了一种利用双反射镜的无线光系统结构。针对双反射镜到接收端的短轴跟踪控制设计了滤光片转盘模块,通过给反射光斑施加频率扰动的方式来实现对相机探测面上双光斑的辨别,并以探测面上双光斑的重叠情况作为判别光束对准的依据。对于存在偏移的重叠双光斑图像,提出多光斑/重叠光斑中心提取的思路,利用最小二乘法椭圆拟合实现重叠光斑的分割,并对无重叠、较少重叠以及较多重叠三种情况下的光斑图像进行分割实验。研究结果显示,在光斑重叠的场景下,光斑中心定位与实际位置之间的标准差小于0.5 pixel,因此所采用的算法在重叠光斑的分离方面具有很好的效果。     

多角度偏振成像仪遥感图像太阳耀斑区的拖尾校正方法

为了有效校正星载偏振相机成像时太阳耀斑区产生的拖尾,以高分五号卫星多角度偏振成像仪为例,结合多角度偏振成像仪在轨成像特点,理论分析了图像获取过程中拖尾产生的机理.建立了光斑区不含饱和像元情况下能够有效对漏光拖尾进行校正的矩阵法与暗行法校正模型,以及光斑区全像元饱和情况下结合矩阵法与暗行法估计光斑区饱和像元强度的遗留拖尾校正模型,该算法充分考虑了强光饱和条件下太阳耀斑区产生的漏光拖尾与遗留拖尾.利用实验室积分球光源成像光斑模拟在轨运行时遥感图像太阳耀斑开展拖尾校正方法可行性验证实验.实验结果表明,该方法不仅能有效去除图像中的拖尾噪声,提高图像质量,而且能够对光斑饱和像元强度进行有效估计.最后,分析多角度偏振成像仪在轨成像图中耀斑区拖尾对其辐亮度测量精度的影响,分析结果表明,拖尾校正前后,灰度方差由202.69×10^6下降至2.32×10^6,平均梯度由5.08×10^-1下降至2.26×10^-1.     

合成孔径雷达图像反演海面风向新方法的研究

提出了利用基于Tikhonov正则化的二维数值微分方法来反演合成孔径雷达图像海面风向的新方法. 首先将高分辨率合成孔径雷达图像去噪、降采样并分割成数个子图像,利用基于Tikhonov正则化的二维数值微分方法求解所关注子图像每一个点的梯度方向,在此基础上通过带有距离权重的目标函数确定子图像整体强度的梯度方向,该梯度的垂线方向就是所要求解的风向,然后进行模拟试验,在添加误差为10%的随机扰动情况下,分别基于Tikhonov正则化的二维数值微分方法与基于有限差分的Sobel算子方法来反演风向,结果表明,前者误差为0.7293°,后者误差为13.5069°,最后进行了实例试验,结果显示,Sobel算子方法的部分风向反演结果偏离整体风向明显,而基于Tikhonov正则化的二维数值微分方法的风向反演结果一致性较好. 将三个船舶报风向与相应位置合成孔径雷达图像的海面风向反演结果进行对比,Sobel算子方法的风向反演结果平均误差在9.0331°,而基于Tikhonov正则化的二维数值微分方法的风向反演结果平均误差仅为1.1148°. 关键词： 合成孔径雷达 海面风向 数值微分 Sobel算子     

利用地球红外辐射的旋转飞行体姿态估计方法

针对导航控制系统对姿态测试技术多元化、新型化和低成本的要求, 提出了一种基于地球红外辐射的旋转飞行体姿态估计方法. 首先, 根据地球红外辐射的产生机理, 结合红外辐射在大气中的传播规律, 建立了地球红外辐射模型. 然后, 分析了旋转飞行体的运动特征, 构建了红外传感器的测量模型. 为了探索红外传感器的输出信号与旋转飞行体的姿态信息之间的内在联系, 研究了不同姿态角和视场角下的传感器输出信号特征. 最后, 为了提高旋转飞行体的姿态测试精度, 设计了基于三轴红外传感器的扩展卡尔曼滤波算法来估计姿态角和横滚角速度. 结果表明: 利用地球红外辐射场进行姿态测试的方法有效可行, 俯仰角估计误差在±0.1°, 横滚角估计误差在±0.05°, 横滚角速度估计误差在±1 rad/s. 该姿态测量方法简单有效, 能够满足旋转飞行体的姿态测量要求.     

折反射全向相机镜面位姿的自标定方法

在已知镜面和透视相机参数的情况下,提出一种不需要任何其他标定物的折反射全向相机镜面位姿的自标定算法,只需要折反射相机采集任意一幅图像即可估计出反射镜面与透视相机之间的旋转和平移。利用镜面外边缘所成的像,通过平面圆位姿估算方法获得两个候选位姿;再利用透视相机镜头边缘的成像,同时进行镜头边缘参数估计和镜面位姿选择。该标定方法操作简单,精度高,适用于非单视点相机的标定。仿真和真图实验结果证明了该方法的有效性。     

视线跟踪输入及其图像处理

介绍了视线跟踪输入人机交互系统的原理和构成,特别是数字图像处理技术在其中的应用。以辅助光源在人眼角膜上的普尔钦斑点及瞳孔偏移为依据,通过对实验照片进行图像处理及分析来检测和判断视线输入方向。提出了在使用过程中在头部微小变动时视线输入方向的修正方法。同时也阐述了通过眼睛盯视实现对计算机外设的控制。结果表明,视线跟踪输入实现了人眼与计算机之间的实时信息交互,为今后以眼动输入作为人机交互手段的自适应平台的开发打下了一定的基础。     

The modelling of the influence of a corneal geometry on the pupil image of the human eye

In normal conditions, a pupil of the eye is observed through the optical system of the cornea. The cornea is the anterior surface of the eye and is the major refractive element of the human eye. The influence of the corneal shape should not be neglected in measurements of the pupil size. The purpose of this study was to estimate the influence of the corneal geometry, the diameter of the pupil and its position in the anterior chamber on the magnification and position of the image of the pupil. The numerical calculations presented in the paper assume infinitely thin cornea, and the corneal topography was approximated by the elongated ellipsoid. The ray tracing procedure was used in our numerical modelling. The magnification of the pupil image amounted to about 10% and increases with decrease of radius of curvature and eccentricity of the corneal profile and decreases for the largest pupil. The results show also that the pupil image is placed nearer the corneal apex than the real pupil. The image of the pupil is always blurred, which limits the sharp observation of the pupil.     

Localization of iris in gray scale images using intensity gradient

A new method of iris localization based on intensity value analysis is proposed in this paper. Iris recognition systems are mainly dependent on the performance of iris localization processing. Steps after localization involve normalization, feature extraction and matching. These steps are based on the accuracy and efficiency of localization of iris in human eye images. In the proposed scheme, the inner boundary of iris is calculated by finding the pupil center and radius using two methods. In the first method, selected region is adaptively binarized and centroid of the region utilized for obtaining pupil parameters. Edges are processed to detect radius and center of pupil during the second method. For outer iris boundary, a band is calculated within which iris outer boundary lies. Signals in one dimension are picked up along radial direction within determined band at different angles. Three points with maximum gradient are selected from each signal. Redundant points are deleted using Mahalanobis distance and remaining points are used to obtain the outer circle of the iris. Points for upper and lower eyelids are found in the same way as the iris outer boundary. Selected points are then statistically fitted to make parabolas and lastly eyelashes are removed from the image to completely localize the iris. Experimental results show that proposed method is very efficient and accurate.     

Design of a computer game using an eye-tracking device for eye's activity rehabilitation

An eye mouse interface that can be used to operate a computer using the movement of the eyes is described. We developed this eye-tracking system for eye motion disability rehabilitation. When the user watches the screen of a computer, a charge-coupled device will catch images of the user's eye and transmit it to the computer. A program, based on a new cross-line tracking and stabilizing algorithm, will locate the center point of the pupil in the images. The calibration factors and energy factors are designed for coordinate mapping and blink functions. After the system transfers the coordinates of pupil center in the images to the display coordinate, it will determine the point at which the user gazed on the display, then transfer that location to the game subroutine program. We used this eye-tracking system as a joystick to play a game with an application program in a multimedia environment. The experimental results verify the feasibility and validity of this eye-game system and the rehabilitation effects for the user's visual movement.     

The curvature measurement of the human eyeball

The curvature of the cornea in the ophthalmology field is essential data, especially for humans when they are being tested for wearing contact lenses, or for patients undergoing refractive surgery by either knife or laser. It is extremely difficult to measure the curvature of the eye precisely because the measurement of the cornea, using a contact tool, is not possible. In this paper, we propose a method to measure the curvature using lens aberration theory and an image processing technique. We project a circular grating, known as a Placido disc, on to the cornea. The reflective image does not have equal divisions and this distortion value contains the curvature information.     

Influence of intraocular pressure on geometrical properties of a linear model of the eyeball: Effect of optical self-adjustment

In general, visual acuity does not change with variations in intraocular pressure. Experiments in vitro as well as our clinical findings lead us to hypothesise that the eyeball could possess certain mechanical properties enabling it to automatically produce a sharp image on the retina despite variations in intraocular pressure. Previously reported simple biomechanical models of the eye did not confirm this hypothesis. Here, we propose a generalised mechanical model of the eyeball in which we include an appropriate limbus ring that mimics the ciliary body and the iris. The Finite Element Method is used to model the eyeball and to test its behaviour. A set of geometrical and material parameters has been determined for the model so that the postulated function of the eye is preserved. Numerical simulations have confirmed the hypothesis. The anatomically justified inclusion of the limbus ring in the proposed model of the eyeball makes it more realistic than those previously reported.     

Automatic localization of pupil using eccentricity and iris using gradient based method

This paper presents a novel approach for the automatic localization of pupil and iris. Pupil and iris are nearly circular regions, which are surrounded by sclera, eyelids and eyelashes. The localization of both pupil and iris is extremely important in any iris recognition system. In the proposed algorithm pupil is localized using Eccentricity based Bisection method which looks for the region that has the highest probability of having pupil. While iris localization is carried out in two steps. In the first step, iris image is directionally segmented and a noise free region (region of interest) is extracted. In the second step, angular lines in the region of interest are extracted and the edge points of iris outer boundary are found through the gradient of these lines. The proposed method is tested on CASIA ver 1.0 and MMU Iris databases. Experimental results show that this method is comparatively accurate.     

A new data processing and calibration method for an eye-tracking device pronunciation system

In this paper, a new data processing and calibration method for a pronunciation system of an eye-tracking device is described. The eye-tracking device was created using both head mounted display (HMD) technology and remote operation capabilities. A pattern recognition computer program was used to distinguish the pupil position and calculate its coordinates.This system can be adapted to provide a digital speech function. A new method for processing the image of the eye in the PC-based system was also developed. With one video CCD camera and frame grabber analyzing a series of human pupil images while the subject is gazing at the screen, an auto-calibration algorithm is used to obtain the direction of the eye gaze in real time. The computers provide the speech sound according to the location where the eye gazes exceed 0.5 s. The availability of multipurpose in this eye-tracking system with very simple equipment will be reconfirmed for future advanced research.     

基于特定感兴趣区采样的虹膜定位改进算法

从虹膜图像特点出发,以瞳孔形心为辅助点实现对虹膜图像特定感兴趣区采样.并且根据虹膜内外圆半径的生理特点设定Hough变换半径参量,依据虹膜内外圆近似同心圆来筛选与虹膜外圆最匹配的Hough变换结果.该算法在主动避开眼皮,睫毛干扰的同时又显著降低了Hough变换的计算量.通过对中科院自动化所CASIA虹膜数据库108组图像的虹膜定位测试结果表明,该方法平均定位时间0.83 s,定位准确率98.9%.     

基于个体眼光学结构的角膜与晶状体的像差补偿

研究角膜对晶状体波前像差的影响对现行的个性化视觉矫正手术有-定的参考价值.运用光学设计软件Zemax,根据个体人眼的角膜地形图、眼内各部分轴向间距和全眼波前像差数据,为22只人眼构建了个体眼光学结构.基于个体眼光学结构和衍射光学理论计算了眼内、外不同位置处的波前,获得了角膜对晶状体波前像差的影响.结果表明,角膜和品状体像差存在补偿和叠加两种关系.大多数眼睛,角膜对晶状体像差有一定补偿作用.总体像散的均方根(RMS)值比品状体像散的RMS值减小0.08～1.48μm,相当于10.1%～77.5%.总体高阶像差的RMS值比晶状体高阶像差的RMS值减小了0.06～0.85 μm,相当于3.8%～79.4%,平均减小了50.7%.其中,球差和彗差的Zernike系数绝对值总体比晶状体分别减小了0.02～0.60μm和0.01～0.39μm,相当于4.3%～98.4%和2.5%～91.4%.