An automated Hirschberg test for infants

A novel automated method to measure eye misalignment in infants is presented. The method uses estimates of the Hirschberg ratio (HR) and angle Kappa (the angle between the visual and optical axis) for each infant to calculate the angle of eye misalignment. The HR and angle Kappa are estimated automatically from measurements of the direction of the optical axis and the coordinates of the center of the entrance pupil and corneal reflexes in each eye when infants look at a set of images that are presented sequentially on a computer monitor. The HR is determined by the slope of the line that describes the direction of the optical axis as a function of the distance between the center of the entrance pupil and the corneal reflexes. The peak of the distribution of possible angles Kappa during the image presentation determines the value of angle Kappa. Experiments with five infants showed that the 95% limits of agreement between repeated measurements of angle Kappa are ± 0.61 (°). The maximum error in the estimation of eye alignment in orthotropic infants was 0.9 (°) with 95% limits of agreement between repeated measurements of 0.75 (°).     

一种基于人脸核心特征的PCA人脸识别算法及应用

传统的PCA人脸识别算法是直接从图像中提取人脸进行识别,由于人脸的大小、角度,光照等原因导致识别率低。本文提出的基于人脸核心特征的人脸识别算法是通过人脸核心特征,包括左眼、右眼、鼻子、嘴巴进行人脸识别。这种算法能有效克服人脸识别中的大小、角度、光照等不利因素,显著提高了人脸识别率,并成功应用于智能相片搜索系统。     

Automatic pupillometry from digital images

Determination of two-dimensional characteristics of the anterior surface of the eye is becoming increasingly important in modern optometry and ophthalmology practice. In particular, accurate estimation of the pupil size and centration is crucial in customized refractive surgery, corneal transplantation, and advanced contact lens fitting. The pupil parameters change under different lighting conditions so they often need to be related to some fixed reference such as the limbus outline. However, current commercial pupillometers do not estimate limbus position. We present a novel algorithm for automatic extraction of pupil parameters from digital images that takes the relative limbus information into account. The algorithm utilizes several customized image processing techniques that form a robust procedure which performs well for a wide range of clinical images. We apply the developed algorithm to images obtained by a standard digital camera, and specialized ophthalmic instruments such as a wavefront sensor and a high-speed imaging system.     

眼轴及眼前节SS-OCT一体化成像系统

针对现有眼轴测量仪器无法同时实现大量程眼轴测量及眼前节成像的功能,设计了眼轴和眼前节同步测量的大量程扫频光学相干层析成像系统。该系统通过设计大量程扫频光源增加成像深度,并在外部设计搭建标定光路进行k域重采样以提高大量程干涉范围内的成像质量,从而在获取高精度眼轴信息的同时对眼前节成像;针对该系统OCT图像信噪比较低的问题,文中采用基于各向异性滤波的保边去噪算法对图像中的散斑噪声进行抑制以提高图像对比度。系统分别使用等比例人眼模型和离体鱼眼进行成像实验,实验结果表明:该系统成像深度可达到69 mm,在精准测量眼轴纵向五层结构的同时完成12 mm范围内的眼前节横向扫描,眼轴长度平均测量误差0.04 mm,成像时间约为0.45 s,满足临床医学应用中实时性的要求。     

Numerical model of heat transfer in the rabbit eye exposed to 60-GHz millimeter wave radiation

A numerical model of the anterior chamber of the rabbit eye is presented. The model takes into account both the fluid dynamics of the aqueous humor and the realistic boundary conditions at the interface of the cornea with the environment. The model is used to determine the temperature distribution and velocity field under 60-GHz millimeter wave radiation. The maximum predicted temperature (45.8 (°) C for an incident power density of 475 mW/cm(2)) is in good agreement with experimental results. Moreover, the model shows that there is a value for the incident power density (about 100 mW/cm(2)) for which the direction of aqueous humor flow due to buoyancy is inverted, because of the inversion of the temperature gradient in the anterior chamber of the eye. This phenomenon has already been reported from experimental observations and can be numerically studied, if aqueous humor fluid dynamics are taken into account in the heat-transfer model.     

基于梯度向量流场的眼睛特征提取

根据人脸图像的边缘梯度图提出了一种新的基于梯度向量流场的眼睛特征提取方法。该算法改进原有的梯度向量流迭代方程求解梯度向量流场,以梯度向量流场中的汇点作为候选点,通过人脸器官的几何位置关系等方法评价候选点以定位眼球。该算法能较好地容忍一定的光照变化、人脸的小角度倾斜和旋转、闭眼和眼镜等干扰。在具有以上干扰的ORL人脸库的400幅图像上的实验证明,该算法具有较好的眼睛特征抽取能力。     

一种红外条件下的新型眼睛状态识别算法

针对复杂光照、头部转动和戴眼镜对眼睛状态识 别算法的影响,提出了一种基于红外图像和形态学的眼睛状 态识别算法,通过带850nm窄带带通滤光片的红外摄像头采集眼睛图 像,提取眼睛轮廓特征描述子和眼睛骨架图像的方向 链码实现睁眼和闭眼判别,同时引入图像可信度判别机制,把眼睛划分为睁开、闭合和 不可信3种状态,从而极大地 降低了算法模型在恶劣环境中的虚警率。实验证明,本文算法模型对于复杂光照、头部转动 和戴眼镜等均具有较高的鲁棒性,在 可信眼睛图像集中,睁眼正确识别率达到了95.21%,闭眼正确识别率 达到了92.03%,均高于其他几种常用的眼睛状态识 别算法,同时每秒能处理200张以上眼睛图像,满足实际驾驶环 境中 实时性的要求。     

High-Density Directional Display for Generating Natural Three-Dimensional Images

A high-density directional display can produce natural three-dimensional(3-D) images by projecting a large number of directional images using directional rays. When the angle pitch of the directional rays is 0.2/spl deg//spl sim/0.4/spl deg/, more than two directional rays passing through a point in 3-D space enter the viewer's eye simultaneously so that the viewer's eye can focus on that point. No discrepancy appears between the convergence function and the accommodation function so that the display does not induce visual fatigue. Two different system configurations are presented: a projection configuration and a thin configuration. A prototype display based on the projection configuration was constructed. The prototype display displayed 64 directional images with directional rays having a horizontal angle pitch of 0.34/spl deg/. The screen size was 9.2 in. The preliminary experimental results showed that a viewer could focus on 3-D images produced by the prototype display.     

Perceptual Image Indexing and Retrieval

We describe a perceptual approach to generating features for use in indexing and retrieving images from an image database. Salient regions that immediately attract the eye are large color regions that usually dominate an image. Features derived from these will allow search for images that are similar perceptually. We compute color features and Gabor color texture features on regions obtained from a multiscale representation of the image, generated by a multiband smoothing algorithm based on human psychophysical measurements of color appearance. The combined feature vector is then used for indexing all salient regions of an image. For retrieval, those images are selected that contain more similar regions to the query image by using a multipass retrieval and ranking mechanism. Matches are found using the L₂ metric. The results demonstrate that the proposed method performs very well.     

一种改进的交叉眼角度欺骗技术

文中研究了多阵元天线角度干扰技术和交叉眼，建立了多阵元交叉眼干扰模型，提出了多阵元交叉眼角度欺骗改进算法，改善了交叉眼干扰角的稳定性和准确性、增加了角度欺骗的范围，同时此算法可以控制干扰角的方向。计算机仿真结果验证了算法改进的有效性和角度干扰的稳定性。     

卡塞格伦镜头的猫眼效应激光反射特性

卡塞格伦(Cassegrain)及类卡塞格伦式光学镜头在光电装备中应用广泛.为了研究具备卡塞格伦式光学镜头的光电装备所特有的猫眼效应特性,采用ZEMAX光学设计分析软件建立了卡塞格伦镜头反射模型,利用物理光学传输方法仿真分析了其猫眼效应反射特性,并得出了猫眼效应可探测入射角范围.对一特定卡塞格伦镜头进行了激光辐照实验,得到了猫眼效应反射光斑图像,测试了猫眼效应绝对反射率以及反射光发散角.结果表明,当发射系统位于该卡塞格伦镜头的视场内时,可以探测到猫眼效应反射光,中心遮挡造成原路返回处光强分布中心能量降低,猫眼效应绝对反射率为11.48%,反射光发散角为3.3 mrad,按照假设条件可以满足30 km内激光主动探测的需要.     

Cell culture imaging using microimpedance tomography

We present a novel, inexpensive, and fast microimpedance tomography system for two-dimensional imaging of cell and tissue cultures. The system is based on four-electrode measurements using 16 planar microelectrodes (5 microm x 4 mm) integrated into a culture chamber. An Agilent 4294A impedance analyzer combined with a front-end amplifier is used for the impedance measurements. Two-dimensional images are obtained using a reconstruction algorithm. This system is capable of accurately resolving the shape and position of a human hair, yielding vertical cross sections of the object. Human epithelial stem cells (YF 29) are also grown directly on the device surface. Tissue growth can be followed over several days. A rapid resistivity decrease caused by permeabilized cell membranes is also monitored, suggesting that this technique can be used in electroporation studies.     

Figure of merit for low frequency anechoic chambers based onabsorber reflection coefficients

Return loss as a function of frequency and angle of incidence is studied to determine the effectiveness of the absorbing material used in an anechoic chamber. This alone is not enough to determine a figure of merit for an anechoic chamber or to compare the figure of merit for one anechoic chamber to that of another. While the information gained from return loss calculations and measurements as a function of angle of incidence is valuable, an overall measure of anechoic chamber effectiveness is necessary in order to compare different designs. In this paper, a new chamber figure of merit which is based on the decay time of the chamber is introduced. This decay time is, in turn, based on the average power absorbed by the chamber walls. The resulting model is simple and does not require intensive numerical computation. Calculations of the figure of merit for anechoic chambers which contain different types of absorbing materials are shown, and calculated and measured values of decay time for a primary standards calibrations facility are compared     

基于梯度积分投影和最大期望算法的人眼定位

针对传统积分投影方法易受眉毛、睫毛、阴影、遮挡及噪声等干扰的问题,提出了一种梯度积分投影与最大期望(EM)算法相结合的人眼精确定位方法,可以在人脸图像中分割出人眼区域,并精确定位人眼位置。首先,采用一种新的梯度算子计算人脸图像的行梯度积分投影粗略定位人眼区域;然后计算人眼区域的列梯度积分投影函数,用EM算法将所得列梯度积分投影函数曲线拟合成两个高斯曲线,并根据高斯曲线精确分割出人眼窗口;最后,利用我们提出的加权质心法在所得人眼窗口中精确定位双眼位置。在YaleB人脸数据库及自采数据库上的实验结果表明,本文方法不易受眉毛及噪声干扰,并能有效克服眼睑和睫毛的遮挡,对不同光照条件及头部姿态都有很好的鲁棒性。     

大角度平面旋转人眼定位方法

提出一种解决平面大旋转角度人脸眼睛精确定位算法,首先根据圆周旋转不变性,建立基于圆周块子矩阵的标准人脸旋转模板.使对旋转角度的判定转化为对圆周块子矩阵移位距离的估计;然后用基于人脸结构关系的方法粗定位时,提出自适应的最优阈值方法去除噪声点,减少匹配误差,减少运算量,提高运算速度;最后对候选区域提取gabor特征,进行精确定位.在FRVT库上的实验结果表明,该算法适用于360°内的平面旋转的人眼定位,算法简单,运算速度快,准确率可达到87.67%.     

一种基于椭圆投影的非理想虹膜定位算法

人以正常步行速度通过采集装置会出现非理想的虹膜图像.本文针对非理想虹膜中的角度偏离图像,提出了一种基于椭圆投影的虹膜定位算法.该算法首先计算双眼相对位置来决定头部的旋转角度,之后找到瞳孔内一点,从该点出发根据梯度变化搜索到虹膜的内边界点,采用最小二乘法拟合椭圆形内边界.然后依据椭圆与圆形的近似度检测人眼凝视方向,使用投...     

视线跟踪系统中眼睛睁闭检测算法研究

眼睛睁闭检测在视线跟踪系统中具有重要意义.为提高检测的准确性,提出了一种基于Harris算子的检测方法.该方法首先利用Harris算子计算图像的角点量,然后搜索图像中角点量最大的位置,以该位置为中心,设置一个区域,统计该区域内角点量总和占整幅图像角点量总和的比例,通过将该比例与阈值相比较来确定眼睛的状态.实验结果表明,...     

基于近红外眼周图像有用特征的人类身份识别研究

针对现存身份识别算法很少有效利用眼周图像的问题,本文执行了两组实验探究人类如何分析眼周图像。首先,选择和预处理用于实验的眼睛图像;然后,以对象随机配对的方式创建不同对象的查询,发现志愿者能对92%的查询正确确定两幅图像的关系;最后,在形成不同对象对时考虑了多个因素,从具有相同年龄和种族,类似的眼睛颜色、眼妆、睫毛长度和眼睛遮挡的对象对形成查询,并且限制志愿者观察查询对的时间。实验取得的正确验证率为79%,分析结果表明,在现有身份识别系统中合并使用眼周识别算法可以更加准确有效地进行人类身份识别。     

交会对接微波雷达高精度测角算法

交会对接微波雷达需要完成100 km至20 m距离范围内、(±60°)×(±60°)宽视场范围内的角度测量,且测角精度要求在0.05°以内。针对兼具远近距离和宽视场测角需求,本文提出一种十形干涉仪几何对消测角算法。针对远距离测角精度无法满足精度要求的问题,采用基于当前统计模型的自适应Kalman滤波算法来提高测角精度。模拟试验、暗室试验和外场挂飞试验表明:干涉仪几何对消测角算法有效、可行,Kalman滤波后的角度测量结果优于高精度交会对接任务需求,已成功应用于月球轨道交会对接。     

一种结合分离滤波器与局部二进模式的快速人眼定位方法

为了解决低质量人脸图像中的快速人眼定位问题,提出一种结合分离滤波器与局部二进模式(LBP)的快速人眼定位算法,该方法快速有效地计算多尺度局部二进模式(LBPs)值,并且利用串级的思想,结合分离滤波器与LBP,进行快速精确的人眼定位.仿真实验表明,与一般的LBP方法相比,该方法在保证人眼定位精度的同时,具有更快的计算速度,在BiolD人脸库中,在两个尺度上计算,平均每幅人脸图像的计算时间下降近40%.