基于图切割的相位展开

剪切散斑干涉术中,普遍采取相移法提取相位,只可得到被包裹的相位信息,进一步量化计算之前,必须展开相位,但是大量的散斑噪音使相位展开变得非常困难.本文提出基于图切割理论的相位展开算法,将相位展开等价于整数的最优估计问题,通过最小化能量函数展开相位,无需对散斑包裹相位图进行滤波,就可以从包含大量散斑噪音的包裹相位图中准确地提取出真实相位,极大程度地保留了相位包裹图中的细节信息.对于同一幅模拟的散斑包裹相位图,传统的质量导向枝切法和最小二乘法的均方根误差分别为11.707 6和4.977 5,新算法的均方根误差则为0.945 9,数值模拟与实验结果均验证了新算法优良的抗噪性能.     

基于方向图变换的快速不连续相位展开

几何突变导致的相位不连续一直是相位展开中具有挑战的问题。针对这一问题,提出基于方向与变换的快速不连续相位展开算法。在提出的算法中,利用图像的结构张量估计包裹相位图的方向,将方向图进行变换和差分计算得到的可靠的权重系数图作为加权最小二乘法的权重,并使用预处理共轭梯度法迭代求解。该算法可以快速地找出不连续位置,并在不连续分割后的区域进行单独的相位展开,具有很好的识别和展开效果。详细地描述了算法的原理和实现步骤,并对算法进行仿真和实验数据验证。实验结果表明:其相位展开的均方根误差为0.36,证明该算法能够快速、准确地对不连续的包裹相位进行展开。     

基于散斑相位条纹方向的自适应正弦/余弦滤波

结合正弦/余弦(sin/cos)滤波技术提出了依据散斑相位条纹图的条纹方向自动选取滤波窗口大小的自适应滤波法。通过计算散斑包裹相位条纹图的条纹方向,依据相位条纹方向自动选择合适的滤波窗口,对散斑包裹相位图的sin和cos变换图同时进行自适应均值滤波,再通过四象限反正切算法得到包裹相位条纹图。实验结果表明,该滤波法能有效保护条纹相位跳变信息,对于条纹密度变化较大且形状复杂的散斑包裹相位图,仍能进行有效的条纹滤波处理,滤波后的相位条纹图更逼近于原始条纹走向。     

基于平滑样条拟合的相位图像滤波评价方法

在散斑干涉测量中,散斑相位图存在大量散斑噪声,需要对其进行滤波处理。但是,目前存在的滤波评价指标不适用于对单一图像持续滤波过程的判断,难以实现滤波过程的自动化。提出一种基于平滑样条拟合的滤波评价方法,通过对滤波过程中相位图的相位分布进行平滑样条拟合并计算其均方根误差,实现对滤波效果的定量分析,以及对持续滤波过程中的图像滤波完成情况的判断,并采用散斑干涉测量中的实验图像对所提方法进行实验验证。实验结果表明,该方法能有效判断散斑相位图是否滤波完成。最后通过对该方法判断的滤波完成图像进行解包裹处理,进一步验证了该方法的有效性和普适性。     

热传导方程在散斑条纹图相位提取中的应用

去除电子散斑十涉条纹图中的噪声是提取条纹图相位的关键问题.利用热传导方程去除条纹图中的噪声,定性和定量分析了该方法的滤波性能.在此基础上,进一步将MBO算法和热传导方程应用于条纹二值化和相位图平滑过程中,并成功地从单幅模拟条纹图中提取了条纹图的相位.研究结果表明,热传导方程能有效减少散斑条纹图中的噪声,改善二值条纹图的边界.进而获得准确的相位分布.     

基于边缘检测的最小不连续相位展开算法

为克服Fylnn最小不连续相位展开算法效率较低的缺陷,以快速高效地展开包裹相位图,提出了一种基于边缘检测的最小不连续相位展开新算法.先对孤立噪声点预处理并将其排除在增长环搜寻扫描区域外,然后利用边缘检测技术检测出相位不连续区域,并把其作为扫描区域.由于利用边缘检测使增长环搜寻所需的扫描范围在很大程度上缩小,最小不连续相位展开算法的效率得到了很大提高.详细描述了新算法的原理和实现步骤,并用计算机模拟和实际的包裹相位图来验证其有效性.相位展开结果表明,新算法能正确展开这些包裹相位图,且较最小不连续算法有更高的效率.     

数字图像散斑相关技术的蚁群优化方法

基于蚁群优化方法提出新的数字图像散斑相关算法。该方法模仿了真实蚂蚁从其巢到食物找到最短路径的方式,通过对蚁群优化方法改进,减少迭代次数并改善解的质量。将新的数字图像散斑相关算法应用到计算机模拟的散斑图像和实验获得的散斑图像中,并与广泛使用的Newton-Raphson算法进行了比较。实验结果展示了新算法的精度、可行性和有效性。当数量级为0.01像素,误差离散均方根小于0.002像素。     

基于经验小波变换及核概率密度的物体表面变形测量

采用CCD相机采集物体变形前后的散斑图片,利用一维经验小波变换对散斑图片进行逐行分解,获得一系列的固有分量.根据分解后分量的核概率密度函数提出基于核概率密度的自适应降噪法,去除噪声干扰,提取跟变形信息相关的分量并重构,利用重构后的每一行获得变形前后重构散斑图.采用Hilbert法计算重构后散斑图的相位,对变形前后散斑图相位进行相减,根据相位差进行解包裹获得物体表面变形信息.实验结果表明该方法能够有效地对物体表面变形进行测量,且测量精度较经验模态分解提高4倍.     

散斑干涉相位条纹图的频域滤波处理

为了解决在数字散斑干涉技术测量时,散斑干涉相位条纹图像中大量噪声对相位解包裹结果和精度产生严重影响的问题,介绍了一种条纹正余弦分解和频域低通滤波结合的方法,实现了散斑干涉相位条纹图的高精度滤波。该方法的基本思路是在对相位图像进行滤波处理前,先将相位图通过正余弦函数进行映射转换成两幅图,分别经过频域滤波,然后再合成为相位图。这种分解频域滤波方法可以在滤波的同时,有效保留相位跳变信息。实验结果表明：与传统的图像降噪方法相比,该方法能够在保留图像“尖峰”信息的基础上,较好地滤除图像中的散斑噪声,方法简单有效,有效解决了传统滤波方法应用在相位条纹图中,相图灰度信息丢失10%~40%的问题。     

数字散斑相位图去包裹新算法

提出了一种新的数字散斑相位图去包裹算法,主要针对检测对象为复杂非连续物体这一情况。物体在激光照明下,采用光学相位反相相减图像的方法来检测并标识出相位间断区,并利用改进了的行列去包裹算法。使去包裹过程只在相位有效区域进行,从而准确快速地实现全场有效区域的相位去包裹。与已提出的相位去包裹方法相比,该算法具有计算量小,速度快,并能有效地避开大面积的相位间断区的优点,该方法使数字散斑技术可以方便地应用于工程实际中如对复杂非连续构件的变形、振动等方面的定量分析。     

Modulation analysis in spatial phase shifting electronic speckle pattern interferometry and application for automated data selection on biological specimens

In electronic speckle pattern interferometry (ESPI), for a fast and objective analysis of measurement data which occur with a high repetition rate, an automated data processing is of particular advantage. For this reason, investigations were carried out to determine if the modulation of speckle interferograms can be applied as a quality parameter for the selection of suitable interferogram data for further evaluation e.g. phase unwrapping when spatial phase shifting (SPS) is performed. Six methods for determining the modulation of speckle interferograms are characterised and compared. The applicability of the speckle interferogram modulation as a parameter for mask generation in the unwrapping process of the phase difference is demonstrated by the evaluation of measurement data obtained from experiments with a spatial phase shifting endoscopic ESPI system on a technical surface and on a human gastrectomy specimen.     

Self-marking phase-stepping electronic speckle pattern interferometry (ESPI) for determining a phase map with least residues

Different from most of the electronic speckle pattern interferometry (ESPI) approaches, which involve the correlation fringe formulation followed by speckle noise elimination (or filtering), to develop a wrapped phase map, this study adopts the approach proposed by Creath in 1985 instead. However, Creath's approach is so critical of its applying interferograms, the influence of which is dependent on the robustness of the applied phase-shifting algorithm and the accuracy of the phase shifter. The self-marking technique proposed by Huang and Chou in 2000 is adopted herein to help overcome any unfavorable conditioning, including hysteresis, nonlinearity or plane tilting, of the pieozo-electrical transducer (PZT), to enable the successful implementation of the Creath's method. With its help, the whole phase stepping history of a practical work (i.e., an ESPI experiment for the present study) can be fully recorded and monitored. Thus, the required phase stepping frames can be accordingly decided and their further calculation will yield a phase map with least number of residues.     

散斑条纹图的自适应窗口滤波方法

针对散斑噪声很难用常用的滤波方法进行滤除,在已有等值线滤波方法的基础上,提出一种更优的自适应窗口滤波方法。由于等值线窗口是在条纹方向图的基础上得到的,深入研究条纹方向的求取方法,提出了一种更为可靠的条纹方向求取算法,在得到高精度条纹方向的同时,还能估计出条纹的密度。使用等值线窗口技术,保持了窗口形状的自适应能力,然后利用对条纹密度的估计,根据条纹的宽度来确定滤波窗口的大小,实现了滤波窗口大小的自适应。最后,根据条纹方向和滤波后的图像可以直接得到条纹密度变化较大的单幅散斑图的相位结果。     

Temporal phase unwrapping using orthographic projection

This paper proposes a novel temporal phase unwrapping method which is a generalization of the three commonly proposed approaches: hierarchical, heterodyne, and number theoretical phase unwrapping. The proposed unwrapping method is based on the orthographic projection of wrapped phases from the measurement space to the space of co-dimension 1. In the space of co-dimension 1 all unknown integer period-order numbers are computed simultaneously using a nearest-neighbor search on a fixed constellation of points. The proposed method offers new key insights about relationship between unwrapping success rate, noise limit, and maximum unwrapping range. We give example how the proposed method may be applied in the multiple frequency phase shifting profilometry.     

Weighted least-squares phase unwrapping algorithm based on derivative variance correlation map

Among different phase unwrapping approaches, the weighted least-squares minimization methods are gaining attention. In these algorithms, weighting coefficient is generated from a quality map. The intrinsic drawbacks of existing quality maps constrain the application of these algorithms. They often fail to handle wrapped phase data contains error sources, such as phase discontinuities, noise and undersampling. In order to deal with those intractable wrapped phase data, a new weighted least-squares phase unwrapping algorithm based on derivative variance correlation map is proposed. In the algorithm, derivative variance correlation map, a novel quality map, can truly reflect wrapped phase quality, ensuring a more reliable unwrapped result. The definition of the derivative variance correlation map and the principle of the proposed algorithm are present in detail. The performance of the new algorithm has been tested by use of a simulated spherical surface wrapped data and an experimental interferometric synthetic aperture radar (IFSAR) wrapped data. Computer simulation and experimental results have verified that the proposed algorithm can work effectively even when a wrapped phase map contains intractable error sources.     

调制度分析在等步长相移法相位展开中的应用

推导了两种常用等步长相移算法的调制度表达式,提出一种新的调制度分析方法。该方法用于等步长相移法中基于加权最小二乘法的相位展开,能够充分利用调制度信息,构造二值和小数权重,从而增强相位展开过程对多种干扰因素的免疫力。实验结果说明了该方法的有效性和实用性。最后比较了二值权重和小数权重在加权最小二乘法的相位展开中的性能表现。     

基于分支设置的质量导引相位展开算法

二维相位展开方法是近年来较为活跃、引起关注的一个研究课题,它在许多测量应用中有着重要的作用。尽管掩膜阻断算法在多个领域都有成功应用实例,该算法存在着固有的缺陷。为了克服掩膜阻断算法的缺陷,综合分支阻断方法和质量导引方法的优点,提出一种基于分支设置的质量导引相位展开新算法。它先以一个初始质量图来引导分支的设置,然后把分支对应的相位质量设置为最低,从而产生一个新的质量图,最后按新质量图来引导相位展开,并使用几个包裹相位图来验证此方法的有效性。计算机模拟相位图和实际相位图的相位展开结果表明,在存在复杂轮廓不连续和高噪声的情况下,该算法优于模板阻断算法,能得到较好的相位展开结果。     

Automatic analysis of three-dimensional displacement field using ESPI

Electronic speckle pattern interferometry (ESPI) has been used to study the in-plane and out-of-plane displacements of the object. In order to improve the accuracy, a Fourier filtration algorithm has been used to remove the speckle noise and get the holographic-quality ESPI fringe pattern. The processing steps of this method are described in detail in this paper. In addition, a phase shifter, which is easily used with simplified structure and high stability, is also presented. It can be applied to various coherent arrangements in experiments to obtain phase shifted fringe patterns. Experiments of determining the 3D displacement field of a circular fixed plate with a uniform load have been carried out using these methods. The results presented in this paper indicate that the accuracy of this method is satisfactory.     

含噪声包裹相位图的加权最小二乘相位展开算法研究

二维相位展开广泛应用在精密光学测量、自适应光学、合成孔径雷达、图像处理等领域中。为处理含噪声包裹相位图,以预条件共轭斜量法求解权重最小二乘相位展开方程。引入非加权二维离散余弦变换求解泊松方程得到的最小二乘相位解作为共轭斜量法的初始解,从而加快了收敛速度,同时提出一种新质量图确定算法求解过程中的权重项。计算机模拟和试验表明算法计算速度快,能有效地消除传统路径积分法在处理信噪比低包裹相位图时的"拉线"现象,是一种有效的相位展开方法。