数字全息粒子图像测速技术应用于旋转流场测量的研究

将数字全息粒子图像测速(DHPIV)技术应用于旋转流场的三维空间速度测量当中。提出了一种新的焦平面定位方法,即综合灰度梯度法,对数字全息中粒子的焦平面进行精确定位,获得了粒子的空间坐标。针对数字全息粒子图像测速技术中的粒子匹配问题,采取三维互相关算法对流场中的示踪粒子进行空间匹配。将基于综合灰度梯度法和三维互相关算法的数字粒子图像测速技术运用到旋转流场全息图中,获得了局部的三维可视化速度场,与理论模型吻合很好。结果表明,该技术能够很好地应用于旋转流场的测量研究当中。     

激光扫描共聚焦显微镜自动对焦研究

目的：针对激光扫描共聚焦显微镜在二维平面扫描样本时不能自动准确定位焦平面的不足,提出一种基于全自动光学显微镜自动聚焦原理的数字图像处理算法解决这个问题。方法：利用激光扫描共聚焦最微镜获得具有一定厚度的显微样本不同焦距下序型固傻,首先应用灰度方差算子全局搜索进行粗聚焦,对粗聚焦得到的焦平面附近各一个扫描步距范围内的图像再利用基于Sobel梯度的熵函数进,行目标区域的精确聚焦,单向搜索以提高聚焦速度.结果：实验表明该方法对于无荧光标记的样本的均可以准确对焦,粗细两次聚焦可以提高自动对焦的精度,基于Sobel梯度的熵函数对于图像边缘敏感,比以往的空域自动对焦方法更符合生物显微样本对焦精确度高的需求。     

基于小波变换的红外弱小目标检测新方法

针对小波变换不能涉及过多尺度的问题,分析了边缘类型对小波多尺度边缘提取的影响。结合红外目标图像对比度低,噪声大,灰度缓慢变化的特点提出基于Canny算子的梯度相位法。梯度相位法认为边缘不只是在灰度发生突变的地方存在,如果某个区域,灰度沿某个方向缓慢变化,这个区域也存在边缘,只不过可以认为边缘比较粗。经试验此方法对红外图像的小波多尺度边缘提取的质量有明显提高。     

采用粒子群优化粒子滤波的红外目标提取算法

提出了一种新的基于粒子群优化粒子滤波(PSOPF)的红外目标提取算法,将红外目标提取阈值的计算问题看作系统状态估计问题.在粒子滤波的框架下,建立了关于灰度—方差加权信息熵和像素点灰度值的阈值状态空间,建立了基于粒子群优化算法思想的系统状态转移模型,建立了基于红外目标提取效果评价函数的系统观测模型,它有效综合了红外图像中灰度、信息熵、梯度、像素点的空间位置等信息.最后,以粒子的加权平均估计目标提取的阈值.实验结果表明,该方法是有效且稳健的.     

基于灰度梯度分割的机头检测算法

在末制导阶段,提出了基于灰度梯度分割的机头检测算法.首先利用平均梯度算子进行边缘检测,分割出目标区域和目标最亮区域,寻找各区域形心位置,通过判断目标区域形心和目标最亮区域形心位置,检测出飞机轴线,确定出候选机头信息;然后利用序列图像帧间较为稳定的相关特征进行D-S合成,对候选机头信息的可信度进行判断,得出准确的机头信息;最后利用数帧不同姿态的目标红外图像数据进行了算法验证.仿真结果表明:在末制导阶段,基于灰度梯度分割的机头检测算法,可有效地识别出机头,并具有较快的运算速度,可实现实时处理.     

液晶屏线路中导电粒子压合的自动光学检测研究

在薄膜晶体管液晶显示器线路检测中,常通过对线路中的导电薄膜粒子的计数和定位实现其导电性的自动检测。为了解决窄边框线路中粒子密度增大带来的粒子重叠问题,提出一种采用微分干涉成像和掩模法结合k均值聚类的算法,在分离出粒子的亮、暗部后,结合图像熵值和粒子的凸性准确分割出粒子。讨论了聚类簇选值的影响,通过不同粒子密度、不同粒子尺寸的样本检验本文算法,并与以往的梯度结合灰度的方法进行对比。结果表明:本文算法在粒子密度较小的区域能达到92.6%的识别率,在粒子密度较大的区域也能达到86%的识别率,分别比梯度加灰度的方法提高了9.9%和42.7%。解决了粒子重叠的问题,并且对光场和成像效果有更好的鲁棒性。     

基于灰度梯度和反正切函数拟合的亚像素边缘检测算法

在数字图像处理和机器视觉中,边缘检测是一个基本问题和关键环节,因此,精确地检测图像边缘是非常必要的。本文提出了一种基于灰度梯度和反正切函数拟合的亚像素边缘检测算法。首先,通过Canny算子粗略提取输入图像的边缘;然后对初步得到的边缘像素逐点提取灰度梯度方向,以提取的梯度方向为坐标轴正方向建立灰度梯度直角坐标系;最后利用最小二乘法,采用反正切函数拟合图像边缘的灰度梯度,获得亚像素边缘位置。利用Microsoft Visual Studio 2008平台进行实验,结果表明：与基于小波变换及基于Zernike矩的亚像素边缘检测方法相比,本文所提算法定位精度较高,检测速度较快,能够更完整地检测出图像的平滑边缘。     

灰度值不连续图像的边缘检测方法研究

对灰度值不连续图像的边缘检测方法作了研究，把梯度法，门限法和边缘跟踪法等3种方法分别用于目标图像，进行比较并得出了结论。     

一种组合GAUSS-filter、SOBEL、NMS、OTSU 4种算法的图像边缘检测的FPGA实现

边缘检测是分离图像目标主体和背景的主要依据。通过检测图像上灰度显著变化的像素点集合来确定图像的边缘。目前边缘检测的方法大多综合应用两个算法来提高边缘检测质量。本文在FPGA上综合应用GAUSS-filter、SOBEL、NMS、OTSU等多种算法进行图像边缘检测。将原始采集到的彩色图像转换成灰度图像,先对图像进行高斯平滑处理,消除干扰性噪声;应用SOBEL算法计算图像梯度值,再应用NMS算法处理灰度,挑出轮廓边缘梯度值最大的灰度像素集合;最后应用OTSU算法自适应地确定图像门限阈值进行边缘检测。该方法不仅能刻画出图像的边缘,而且还能对边缘进行细化,实验结果显示对不同的图像都有很好的检测效果。本文所提出的在FPGA上实现的图像边缘检测方法具有准确、实时、高速等特点,能够应用到许多领域中。     

一种直边缘物体宽度的图像测量法

提出一种基于方向功率谱与投影梯度的直边缘物体宽度测量方法,通过对目标图像功率谱进行极坐标变换得到方向功率谱,并由此计算出直边缘物体的伸展方向;然后对原始图像按照该伸展方向进行灰度投影,并由投影梯度结果得到待测宽度。该方法无需对目标图像进行边缘检测、阈值分割等预处理操作,因而测量结果更加准确、可靠,且计算量较小、测量效率高。数值模拟与实验结果表明,本文所提方法能够保证1像素的测量精度,且物体长度方向的几何尺寸不影响宽度测量结果。     

Matching Structures by Computing Minimal Paths on a Manifold

The general problem of matching structures is very pervasive in computer vision and image processing. The research presented here tackles the problem of object matching in a very general perspective. It is formulated for the matching of surfaces. It applies to objects having small or large deformation and arbitrary topological changes. The process described hinges on a geodesic distance equation for a family of curves or surfaces embedded in the graph of a cost function. This geometrical approach to object matching has the advantage that the similarity criterion can be used to define the shape of the cost function. Matching paths are computed on the cost manifolds using distance maps. These distance maps are generated by solving a general partial differential equation which is a generalization of the geodesic distance evolution scheme introduced by R. Kimmel, A. Amir, and A. F. Bruckstein (1995, IEEE Trans. Pattern Anal. Mach. Intell.17, 635–640). An Eulerian level-set formulation is also introduced, leading to a numerical scheme used for solving partial differential equations originating from hyperbolic conservation laws, which has proven to be very robust and stable.     

基于随机化视觉词典组和上下文语义信息的目标检索方法

 传统的视觉词典法(Bag of Visual Words,BoVW)具有时间效率低、内存消耗大以及视觉单词同义性和歧义性的问题,且当目标区域所包含的信息不能正确或不足以表达用户检索意图时就得不到理想的检索结果.针对这些问题,本文提出了基于随机化视觉词典组和上下文语义信息的目标检索方法.首先,该方法采用精确欧氏位置敏感哈希(Exact Euclidean Locality Sensitive Hashing,E²LSH)对局部特征点进行聚类,生成一组支持动态扩充的随机化视觉词典组;然后,利用查询目标及其周围的视觉单元构造包含上下文语义信息的目标模型;最后,引入K-L散度(Kullback-Leibler divergence)进行相似性度量完成目标检索.实验结果表明,新方法较好地提高了目标对象的可区分性,有效地提高了检索性能.     

Discernibility criterion in Fresnel projection microscopy

The applicability of the Rayleigh separation criterion in Fresnel electron projection microscopy is studied theoretically. Quantum mechanical simulations of electron scattering by two C60 molecules, at energies of the order of 150 eV, are analysed on the basis of the discernibility criterion of two diffracting apertures. The simple separation criterion derived from Fresnel theory is found to remain pertinent, except for small source to object distances. At these distances, the critical separation distance between the two C60 molecules is such that the 'sucking-in' of the beam between the two nearby C60 molecules cannot be neglected. This leads to a discrepancy with the Rayleigh criterion.     

Salient edge and region aware image retargeting

The purpose of image retargeting is to automatically adapt a given image to fit the size of various displays without introducing severe visual distortions. The seam carving method can effectively achieve this task and it needs to define image importance to detect the salient context of images. In this paper we present a new image importance map and a new seam criterion for image retargeting. We first decompose an image into a cartoon and a texture part. The higher order statistics (HOS) on the cartoon part provide reliable salient edges. We construct a salient object window and a distance dependent weight to modify the HOS. The weighted HOS effectively protects salient objects from distortion by seam carving. We also propose a new seam criterion which tends to spread seam uniformly in nonsallient regions and helps to preserve large scale geometric structures. We call our method salient edge and region aware image retargeting (SERAR). We evaluate our method visually, and compare the results with related methods. Our method performs well in retargeting images with cluttered backgrounds and in preserving large scale structures.     

Parameter space warping: shape-based correspondence between morphologically different objects

This paper presents a novel and comprehensive method for the automated determination of correspondences between two morphologically different two-dimensional (2-D) or three-dimensional (3-D) objects. Correspondences are determined by warping parametric representations of the objects to be matched. The warp is guided by the minimization of a similarity criterion function that measures features related to structural correspondence, including Euclidian point-to-point distance and differences in normals and curvature. The method uses a continuous harmonic parameterization for both the object and the warp, which provides: 1) a high degree of computational efficiency; 2) robust extraction of differential features, not subject to discretization errors or noise amplification in differentiation; 3) direct formulation of constraints to avoid overlaps in the resulting correspondence set; and 4) a scale-space paradigm of object shape and warp. The new method does not search for individual landmarks, but operates with a complete, integrated representation of the object geometry. The method was tested on 2-D and 3-D objects with substantial shape differences. Results demonstrated substantial improvements of 2%-33% in correspondence accuracy and 15%-59% in correspondence quality compared with direct registration methods.     

数字全息显微中自动调焦技术及其应用 （封面文章） （特邀）

数字全息显微技术(Digital Holographic Microscopy, DHM)将光学干涉和光学显微技术相结合,为微观物体的三维形貌、透明物体的厚度/折射率分布提供了一种快速、无损测量手段。数字全息显微可以通过计算机模拟物光波的衍射传播以实现对被测样品的数字调焦。然而,这一过程需要事先知道全息图到物体像面的距离(文中称为离焦距离)。如何自动获得离焦距离一直是数字全息显微技术中的研究热点。为此,文中着重介绍了基于锐度度量、能量集中度、振幅模量分析、稀疏度测量以及不同照明调制的离焦量获取方法。利用该离焦量可以实现对运动样品或动态过程的自动调焦,为运动物体或动态过程的跟踪观测和实时干预提供了有力手段。此外,文中还介绍了数字全息显微自动调焦技术在细胞、三维粒子场上成像、识别和追踪以及生物组织三维成像等方面的应用。     

How far is far?

Recent comparisons of computed and measured backscattering cross sections of cylindrical bodies revealed unexpectedly large discrepancies which were apparently due to the finite range used in the measurements. This led to a reexamination of the farfield criterion for a variety of two-dimensional scatterers and one three-dimensional object. It was found that large errors can be incurred in measurements at the standard far-field distance, especially of bodies characterized by strong edge scattering. Errors as great as 6 dB can occur and it may be necessary to exceed the usual farfield distance by a factor of 5 or more in order to reduce the error to 1 dB.     

A Robust Particle Filter-Based Method for Tracking Single Visual Object Through Complex Scenes Using Dynamical Object Shape and Appearance Similarity

This paper addresses the issue of tracking a single visual object through crowded scenarios, where a target object may be intersected or partially occluded by other objects for a long duration, experience severe deformation and pose changes, and different motion speed in cluttered background. A robust visual object tracking scheme is proposed that exploits the dynamics of object shape and appearance similarity. The method uses a particle filter where a multi-mode anisotropic mean shift is embedded to improve the initial particles. Comparing with the conventional particle filter and mean shift-based tracking (Shan et al. 2004), our method offers the following novelties: We employ a fully tunable rectangular bounding box described by five parameters (2D central location, width, height, and orientation) and full functionaries in the joint tracking scheme; We derive the equations for the multi-mode version of the anisotropic mean shift where the rectangular bounding box is partitioned into concentric areas, allowing better tracking objects with multiple modes. The bounding box parameters are then computed by using eigen-decomposition of mean shift estimates and weighted averaging. This enables a more efficient re-distributions of initial particles towards locations associated with large weights, hence an efficient particle filter tracking using a very small number of particles (N = 15 is used). Experiments have been conducted on video containing a range of complex scenarios, where tracking results are further evaluated by using two objective criteria and compared with two existing tracking methods. Our results have shown that the propose method is robust in terms of tracking drift, tightness and accuracy of tracked bounding boxes, especially in scenarios where the target object contains long-term partial occlusions, intersections, severe deformation, pose changes, or cluttered background with similar color distributions.     

Improved space-time trellis coded modulation scheme on slowRayleigh fading channels

It has been established that the appropriate criteria for space-time trellis coded modulation (STTCM) design on slow Rayleigh fading channels are maximisation of the minimum rank and the minimum determinant of the distance matrices. It is demonstrated that when STTCM is used in systems with a large product (>3) of the numbers of transmit and receive antennas, the design of codes with maximum coding gain is governed by the minimum trace of the distance matrices. A number of new codes based on the proposed design criterion have been constructed and shown to be superior to other known codes     

基于前导脉冲辅助的相位调制1090ES信号载频同步算法

基于相位调制扩容1090ES信号为ADS-B带来新的功能和应用,载波频率同步是扩容信号需解决的一项关键技术。针对扩容1090ES信号的突发载频同步问题,提出了一种基于频偏捕获和相位误差跟踪环的快速同步方法,频偏捕获采用前导辅助脉冲相关性判决进行二叉树频率搜索,捕获载频偏差并校正得到频偏较小的基带信号,相位误差跟踪环实现对小频偏信号进行频率估计和补偿。仿真结果表明:该方法适用于基于相位调制的扩容1090ES信号接收系统。