基于光强传输方程与SLM的快速相位恢复

基于光强传输方程（TIE）的相位恢复技术,可以通过测量一系列垂直于光轴分布的散焦强度图,直接求解得到光场的相位信息。传统的基于TIE的强度图像采集系统在获得散焦图像时需要机械移动。通过在空间光调制器（SLM）上加载透镜相位图,使其实现可编程透镜的功能,任意改变此透镜的焦距值,可以实现不同的散焦距离,从而避免采集图像过程中CCD的移动。根据不同的算法理论,设计了两种光强图像采集系统。由于日常生活中使用相机拍照时,透镜的相位调制作用不可忽略,使用SLM代替含透镜的光传播模型中透镜的作用,设计了第一种实验装置。此外,通过在4f系统的频率域位置放置SLM,设计了第二种实验装置。真实实验的结果验证了这两种方法的有效性和正确性。     

自适应聚焦下基于强度传输方程的相位恢复

基于强度传输方程的非干涉相位恢复方法是通过对强度图像求解方程来获取相位的一种途径。在图像采集过程中,对聚焦图像的选择是很重要的。但该过程通常是由主观方法来确定,从而导致聚焦定位不准确,进而影响相位恢复结果的精度。首先,提出了一种基于强度传输方程的自适应聚焦相位恢复方法;其次,使用边缘占空比对采集图像进行定位,在求解相位之后进行循环角谱传播,直到边缘占空比定位位置不变,即被认为是定位到了最佳聚焦位置;最后,再使用强度传输方程求解样本的相位。结果证明:该方法不仅提高了相位恢复的准确性而且减少了获取大量图像的次数。在模拟实验中,恢复相位与原始相位的相关系数达到0.9866,均方根误差为0.3050。在实际的微透镜阵列实验中,用所提出的相位恢复方法恢复出的微透镜高度与真实高度误差仅为5.7%,证明了在显微成像领域,所提算法可以定位到最优聚焦位置,有利于自动聚焦技术的发展,进而提高相位恢复的精度。     

基于光强传输方程离散余弦变换求解的数字全息相位解调方法

提出了一种基于光强传输方程（TIE）的数字全息相位解调方法,并利用离散余弦变换进行了求解。仿真和实验结果表明,与传统的基于快速傅里叶变换的相位解调方法相比,该方法在没有损失精度的基础上加快了解包裹过程。此外,通过选择一个合适的延拓方案来计算强度的偏导数后,该方法的效率可进一步提高。提出的基于TIE的新型相位解调方法具有较高的处理速度和精度,可以实现相位测量的实时应用。     

传输图像的子波域插值恢复算法

在丢包信道中传输子波编码图像时,存在图像重构问题.本文提出了一种新的图像恢复算法—树恢复子波域插值算法,可以用于恢复丢失的子波树系数.该算法利用二维子波变换具有的水平和垂直方向边缘检测能力,采用数学形态学膨胀运算,恢复已丢失的表示边缘信息的高频系数.为了保持图像边缘的尖锐性和方向性,本文采用了高频系数指导下的低频系数恢复技术.文章最后给出的仿真结果验证了该算法的有效性.     

透镜模型下基于色散和强度传输方程的相位恢复技术

针对基于强度传输方程（Transport of Intensity Equation, TIE）的非干涉相位恢复技术要求光源是单色的限制,以及强度采集过程移动CCD或物体而引入的机械误差,提出了一种适用于透镜模型下的色散相位恢复技术。该方法基于透镜成像系统的相位变换特性,将色散与TIE结合在一起, 使不同波长的光经过透镜系统后在同一位置成像,从而在不机械移动的情况下获得聚焦和散焦强度图像。再利用散焦量与波长的关系结合TIE计算出物体的相位信息。模拟实验中用该方法恢复物体的相位与原始相位的相关性系数为0.970 7,均方根误差为0.061 8;同时真实实验对透镜阵列相位进行了恢复,实验结果与真实参数误差为1.74%,证明了所提方法的正确性和有效性。     

单透镜系统中与色散融合的混合相位恢复方法

相位恢复是利用能观测到的强度信息恢复原始相位信息。强度传输方程（TIE）作为一种传统的非干涉相位恢复技术,只需通过测量至少两个相近平面的强度信息即可计算出相位信息。这种方法通常需要通过移动被测物体或摄像机来获取强度图像,不可避免地会产生机械误差。提出了一种新的相位恢复方法:与色散融合的混合相位恢复算法（CD-HPR）。通过设置不同波长的光通过单透镜系统得到物体在同一位置成的像,这样不需要机械运动就能获得聚焦和散焦图像强度,然后结合散焦量与波长之间的关系计算出散焦量,再用强度传输方程计算初始相位信息。角谱迭代算法的使用较好地改进了初始相位值。在仿真实验中,该方法恢复的相位与原始相位之间的均方差为0.1076;同时,通过实验恢复了透镜阵列的相位,实验结果与实际参数的误差为3.4%,证明了该方法的正确性和有效性。该方法扩展了传统方法要求光源为单色的局限性,提高了计算精度。     

基于图像序列的YG算法二维相位恢复

迭代算法相位恢复计算中存在可能陷入局部极小值,导致算法收敛速度慢和不稳定的缺点,为了克服这一缺点,本文利用多个输出平面上光的强度信息,将YG算法推广到空域约束(光强度约束)二维相位恢复问题,提高算法收敛速度.模拟实验结果表明,基于图像序列的YG算法二维相位恢复收敛速度快,相位恢复精度高,同时对噪声具有较好的鲁棒性.     

强度传输方程和角谱迭代融合的相位检索算法

相位检索技术将光学与计算相结合,从强度测量中恢复相位,包括强度传输方程法和角谱迭代法。但前者仅对近场相位的恢复有效,其基于相干照明的假设前提使得该方法不能直接应用于自然场景的相位检索中;而后者具有迭代不确定性、收敛速度慢等缺点。探讨了在相干照明情况下传统强度传输方程法和角谱迭代法相融合的相位检索算法,将该融合法进一步扩展,提出了适用于自然场景透镜模型的相位检索方法,即使用强度传输方程法计算像平面的相位,并将该相位值作为角谱迭代的初始值,根据光路的可逆性,迭代出物面的相位信息,分别给出了两种情况下的实验结果。     

相位共轭补偿大气传输中SBS的阈值效应对目标上光强分布的影响

提出了在用非线性光学技术补偿激光大气传输过程中，利用受激布里渊散射（ＳＢＳ）的阈值效应可以在非配合目标上主动获得小面积的信标光斑。从理论上证明了在存在大气湍流的情况下，阈值效应对目标上信标光强分布的影响。最后分别就最初目标上的光斑是由两个强反射光点组成的光斑和是一个大面积的强度连续分布的光斑的情况进行了实验研究，实验结果与理论相符合。     

湍流退化图像相位恢复算法研究

为克服气动光学效应对目标图像的影响．把相位恢复算法与气动光学效应机理研究结合起来,用于湍流退化图像的恢复。该算法是通过目标图像的傅里叶变换幅值来恢复目标图像,或等价地,恢复傅里叶变换相位。讨论了两类相位复原算法——迭代傅里叶变换（研）和解相关算法。对现有的解相关算法作了改进。采用共轭梯度法解高斯一牛顿方程,可有效提高算法的收敛速度。研算法不能保证迭代过程总能收敛到正确解,有时会出现停滞现象。将研和解相关算法组合起来,可以克服IFT算法的停滞现象,提高正确收敛率。给出了在信噪比为20dB情况下的湍流退化仿真图像恢复的实例,目标图像能较清晰地恢复出来。实验结果表明该算法具有较好的稳定性和抗噪声能力。     

Phase measurement of atomic resolution image using transport of intensity equation

Since the Transport Intensity Equation (TIE) has been applied to electron microscopy only recently, there are controversial discussions in the literature regarding the theoretical concepts underlying the equation and the practical techniques to solve the equation. In this report we explored some of the issues regarding the TIE, especially bearing electron microscopy in mind, and clarified that: (i) the TIE for electrons exactly corresponds to the Schr?dinger equation for high-energy electrons in free space, and thus the TIE does not assume weak scattering; (ii) the TIE can give phase information at any distance from the specimen, not limited to a new field; (iii) information transfer in the TIE for each spatial frequency g will be multiplied by g2 and thus low frequency components will be dumped more with respect to high frequency components; (vi) the intensity derivative with respect to the direction of wave propagation is well approximated by using a set of three symmetric images; and (v) a substantially larger defocus distance than expected before can be used for high-resolution electron microscopy. In the second part of this report we applied the TIE down to atomic resolution images to obtain phase information and verified the following points experimentally: (i) although low frequency components are attenuated in the TIE, all frequencies will be recovered satisfactorily except the very low frequencies; and (ii) using a reconstructed phase and the measured image intensity we can correct effectively the defects of imaging, such as spherical aberrations as well as partial coherence.     

基于小波变换与曲波变换的图像插值

提出了一种组合小波变换与曲波变换稀疏约束的图像插值算法。利用小波变换对图像纹理成份和曲波变换对图像卡通成份的稀疏表示特性,首先将图像插值问题转化成稀疏约束的图像重建问题,然后通过迭代投影对复原最优化问题进行求解,从而实现成份自适应的图像插值。实验结果表明,相比于现在有图像插值算法,本文算法可以显著地提高被插值图像的峰值信噪比(PSNR)和视觉质量。     

Edge-directed interpolation based on shifted-linear image model

This paper presents a hybrid image interpolation algorithm to keep details and edges simultaneously. The basic idea is to separate the unknown pixels into two classes and estimate them in different way. One class of unknown pixels is obtained via shifted linear interpolation and the other class through statistical signal processing method. The merit of this hybrid algorithm is that each unknown pixel can be estimated through original pixels simultaneously. Simulation results demonstrate that this hybrid interpolation algorithm improves the quality of the interpolated images over conventional interpolation methods.     

A unified approach to optimal image interpolation problems based onlinear partial differential equation models

The unified approach to optimal image interpolation problems presented provides a constructive procedure for finding explicit and closed-form optimal solutions to image interpolation problems when the type of interpolation can be either spatial or temporal-spatial. The unknown image is reconstructed from a finite set of sampled data in such a way that a mean-square error is minimized by first expressing the solution in terms of the reproducing kernel of a related Hilbert space, and then constructing this kernel using the fundamental solution of an induced linear partial differential equation, or the Green's function of the corresponding self-adjoint operator. It is proved that in most cases, closed-form fundamental solutions (or Green's functions) for the corresponding linear partial differential operators can be found in the general image reconstruction problem described by a first- or second-order linear partial differential operator. An efficient method for obtaining the corresponding closed-form fundamental solutions (or Green's functions) of the operators is presented. A computer simulation demonstrates the reconstruction procedure.     

Multi-object image retrieval based on shape and topology

We aim at developing a geometry-based retrieval system for multi-object images. We model both shape and topology of image objects including holes using a structured representation called curvature tree (CT); the hierarchy of the CT reflects the inclusion relationships between the objects and holes. To facilitate shape-based matching, triangle-area representation (TAR) of each object and hole is stored at the corresponding node in the CT. The similarity between two multi-object images is measured based on the maximum similarity subtree isomorphism (MSSI) between their CTs. For this purpose, we adapt a continuous optimization approach to solve the MSSI problem and a very effective dynamic programming algorithm to measure the similarity between the attributed nodes. Our matching scheme agrees with many recent findings in psychology about the human perception of multi-object images. Experiments on a database of 1500 logos and the MPEG-7 CE-1 database of 1400 shape images have shown the significance of the proposed method.     

Dictionary based color image retrieval

In this work the normalized dictionary distance (NDD) is presented and investigated. NDD is a similarity metric based on the dictionary of a sequence acquired from a data compressor. A dictionary gives significant information about the structure of the sequence it has been extracted from. We examine the performance of this new distance measure for color image retrieval tasks, by focusing on three parameters: the transformation of the 2D image to a 1D string, the color to character correspondence, and the image size. We demonstrate that NDD can outperform standard (dis)similarity measures based on color histograms or color distributions.     

Hadoop分布式的海量图像检索

传统基于内容的图像检索方法通过相似度测量算法获取检索结果,对海量图像存在检索效率低和精度差的弊端,因此设计基于Hadoop分布式的海量图像检索方法,其基于Hadoop云平台对海量数码图像实施分布式运算,采集图像SURF特征,采用K-Means聚类方法将相似图像SURF特征聚集起来,通过TF-IDF数据挖掘技术对图像特征实施量化,进而基于Hadoop平台中的Lucene框架塑造海量图像数据的索引模块和搜索模块,依据用户输入的图像SURF特征塑造海量图像数据索引,完成相似图像的准确检索。实验结果说明,所提图像检索方法检索出的图像质量佳,对海量图像进行检索的效率和精度高。