用变形全息透镜实现变形分数傅里叶变换

利用一发散点光源和一束倾斜平行光制作出在两个垂直方向上具有不同焦距的变形全息透镜,且用此全息元件实现了变形分数傅里叶变换。变形全息透镜两个方向上的焦距随全息记录条件和再现条件而变化,分析了用这种全息透镜实现变形分数傅里叶变换的条件。实验表明,用该元件能够方便地实现任意级次的变形分数傅里叶变换。     

Multiple information encryption by user-image-based gyrator transform hologram

A novel multiple information encryption by user-image-based gyrator transform hologram is proposed. In encryption process, each channel of the user image is phase encoded, modulated by random phase function and then gyrator transformed to get the gyrator spectrum of user image. Subsequently, each channel of the secret image is normalized, phase encoded, multiplied by modulated user image, and then gyrator transformed to obtain the gyrator spectrum of secret image. The encrypted digital hologram is recorded by the interference between the gyrator spectrum of user image and the spherical wave function. Similarly, the digital hologram for decryption is recorded by the interference between the gyrator spectrum of secret image and the spherical wave function. The multiple encrypted digital holograms are multiplexed into a final encoded hologram and the corresponding digital holograms for decryption are multiplexed into a final hologram for decryption. The wavelength and radius of the spherical wave function, and angle of gyrator transform are all essential keys for decryption. The proposed system has two main features. First, the encrypted hologram has no information about secret image. Second, the hologram for decryption used as identification key. Consequently the two marked security layers of information protection are achieved. The proposal can be realized by optoelectronic system. Numerical simulation results demonstrate the feasibility and security of the proposed technique.     

结合空间和光谱信息的高光谱影像端元光谱自动提取

端元光谱提取是高光谱影像混合像元分解的关键。现有的端元提取方法多是仅利用了影像的光谱信息,忽略了像元间的空间相关性。现有研究基础上,提出了一种结合影像空间和光谱信息的高光谱影像端元光谱自动提取方法(integration of spatial-spectral information based endmember extraction,ISEE)。该方法首先进行影像子空间划分以增强影像局部的光谱信息特征,然后通过特征空间投影分析获得影像候选端元,最后依次在影像空间信息约束下和端元光谱信息约束下进行优化,得到最终的影像端元光谱集。仿真高光谱影像和真实高光谱影像的实验结果表明,结合影像空间和光谱信息的ISEE方法是有效的,且比一些常用方法提取的端元光谱更为准确。     

基于多尺度区域粒度分析的遥感图像分割

针对高分辨率遥感图像中不同地物具有粒度差异的特点,提出了一种多尺度区域粒度分析的图像分割方法。该方法首先使用均值漂移得到图像各尺度上的初始过分割区域,然后通过考虑区域大小和区域间上下文关系进行粒度分析,最后利用马尔科夫随机场模型对图像的粒度信息和光谱信息进行建模,得到分割结果。用平朔地区SPOT5和泰州航拍等遥感图像进行了实验,并与若干考虑光谱特征的分割方法进行了对比,结果表明提出的方法能有效地提高分割精度。     

Measuring causality by taking the directional symbolic mutual information approach

We propose a novel measure to assess causality through the comparison of symbolic mutual information between the future of one random quantity and the past of the other.This provides a new perspective that is different from the conventional conceptions.Based on this point of view,a new causality index is derived that uses the definition of directional symbolic mutual information.This measure presents properties that are different from the time delayed mutual information since the symbolization captures the dynamic features of the analyzed time series.In addition to characterizing the direction and the amplitude of the information flow,it can also detect coupling delays.This method has the property of robustness,conceptual simplicity,and fast computational speed.     

超衍射成像中 双螺旋点扩展函数的三维定位精度

开关效应和单分子定位的结合可以实现样品的超衍射分辨成像, 双螺旋点扩展函数将单分子定位纳米分辨从二维扩展到了三维.本文对双螺旋点扩展函数的三维定位精度展开了探讨.首先, 基于费希尔信息量, 计算了双螺旋点扩展函数的无偏估计, 得出其理论定位精度, 并分析了光子数、背景噪声以及有效像元尺寸大小对其定位精度的影响; 其次, 基于单分子定位实验过程中对于数据分析通常采用的高斯拟合质心定位算法, 通过误差传递函数定律求得双螺旋点扩展函数的轴向定位精度.计算机模拟结果表明, 在光子数大于1000的条件下, 高斯拟合质心定位精度和费希尔信息量理论定位精度符合较好. 本文的讨论不仅为双螺旋点扩展函数的三维定位精度提供了理论依据, 同时也可为实验提供理论指导. 关键词： 双螺旋点扩展函数 费希尔信息量 定位精度 高斯拟合     

径向双折射滤波器的超分辨性能研究

超分辨技术因其可以超越经典的衍射极限而为人们所熟知．并且．在光存储和共焦扫描成像系统中有着广泛的应用。把由两个偏振器和一个圆对称的双折射元件组成的径向双折射滤波器引入超分辨技术,借助琼斯算法推导出其光瞳函数的表达式。由分析得出通过改变径向双折射滤波器中偏振器的偏振方向和双折射元件的主轴之间的夹角,即可实现光学系统的横向超分辨或轴向超分辨。同时对评价该器件超分辨性能的参量第一零点比、斯特尔比和旁瓣强度抑制比做了详细的讨论。该滤波器用于超分辨技术的优点在于其制作不涉及相位的变化而比较简单,且费用比较低。缺点是旁瓣能量过高,但可以通过采用共焦系统来抑制。     

利用频闪结构光测量旋转叶片的三维面形

在对快速甚至高速运动物体进行研究时,需要对运动物体各个时刻的三维面形和形变量进行数字化描述。提出了一种利用频闪光作为结构照明光源,基于傅里叶变换轮廓术对旋转叶片每个时刻的三维面形和变形量进行动态测量的光学方法。使用自行设计的同步控制单元对风扇叶片旋转位置进行检测,用该检测信号同步驱动频闪结构光源的发光和图像采集系统“冻结”记录下旋转叶片表面变形条纹的瞬时图像,再运用傅里叶变换轮廓术计算出每一瞬间时刻旋转叶片的三维面形,分析这些三维面形数字化结果可以进一步得到旋转叶片的变形量。通过对家用电风扇的实验,验证了该方法的合理性和可行性。该方法可望在高速运动物体的面形和变形研究上有广泛运用。     

Edge linking and image segmentation by combining optical and digital methods

We present a hybrid method for segmentation of intensity images, which combines an optical contouring technique and digital algorithms for linking edge points or image segmentation. In a first stage, the digital image to be processed is displayed in a twisted-nematic liquid-crystal display (LCD), which is placed between a polarizer–analyzer pair at 45 deg (instead of 90 deg as occurs in standard LCDs). It is not difficult to demonstrate that the proposed setup produces a resultant image with very pronounced dark contours at middle intensity. After the optical preprocessing, two different digital algorithms are applied: an edge linking algorithm (modified chain code) and a simple thresholding technique for image segmentation. The proposed procedure works well with monochromatic and color images. The method could be useful as a robust technique for segmentation of large images in real-time, which presents potential applications in medical and biological imaging.