仿视觉过程的相位展开方法

在所有基于条纹分析的光学测量中,相位展开问题是难以避免的问题。所有传统的相位展开方法的共同点都是在相主值图中通过邻域内相主值差和寻找无噪声的相位展开路径来完成的。如果不利用整幅图像像素间的联系,则误差会沿展开路径传播。根据人眼识别栅线图周期的过程提出了一种与以往完全不同的相位展开方法。经过初步提取周期分界线、修补分界线和根据分界线确定周期三个步骤即可完成相位展开过程。该算法的原理简单明了,实现起来相对简单,只需单幅条纹图像即可得到周期,因而可用于动态测量。实验结果验证了该算法的可行性。     

时间维相位重建的改进算法

提出了一种时间维-相位重建的改进算法:利用折叠位相图进行时间相位展开以提高算法效率;推导并调整了基于时间相位展开算法初始条件从而减少所需的二维编码条纹图,增加了算法的实时性.从而可以更加有效地解决深度表面不连续和存在隔离物表面拓扑结构的景物相位重建问题.实验结果证明了本文所提出算法的可行性及有效性.     

An Effective Phase Unwrapping Algorithmfor Phase-stepping Interferometry

1.IntroductionInrecentyears,manyinterestshavebeenconcentratedontheproblemofphaseunwrappingforthefringepatternanalysis.Thewrappedphaseisintheformofthetangentfunctioninthecomputer.Thecalculatedphasevaluesarewrappedinto--rsto rs,whilethepracticalphasevaluesarereconstructedafterphaseunwrapping.Ifthecasesof'noise,steepwavefront,lowmodulation,andspeckleexistinthefringepatterns,thephaseunWrappingprocesswillfailthroughtheconventionalphaseunwrappingalgo-rithm[1'2].Asaresult,manystripswillbegeneratedin…     

Phase unwrapping algorithms, respectively, based on path-following and discrete cosine transform

This paper describes a path-following phase unwrapping algorithm and a phase unwrapping algorithm based on discrete cosine transform (DCT) which accelerates the computation and suppresses the propagation of noise. Through analysis of fringe pattern with serious noises simulated in mathematic model, we make a contrast between path-following algorithm and DCT algorithm. The advantages and disadvantages of analytical fringe pattern are also given through comparison of two algorithms. Three-dimensional experimental results have been given to prove the validity of these algorithms. Despite DCT phase unwrapping technique robustness and speed in some cases, it cannot be unwrapping inconsistencies phase. The path-following algorithm can be used in automation analysis of fringe patterns with little influence of noise.     

基于可靠性的相位去包裹算法

提出了一种新的基于可靠性的相位去包裹算法。采用了队列算法及去包裹可靠性的判别标准。与传统方法相比,能够自动避开噪声区域,解决了相位去包裹中的阴影遮挡以及空洞等问题,克服了传统去包裹方法中的误差传播效应,能准确快速地对全场进行相位去包裹。设计了一套基于此算法的三维形面测量系统。     

广义条纹图序列编码的相位重建

为解决拓扑复杂物体三维数字化过程中的绝对相位测量及相位重建问题,提出了一种广义变频条纹图序列的相位展开算法。简要综述了现有的各种时间维相位展开算法并指出这些算法存在的问题,在此基础上,详细分析比较提出方法与正指数条纹序列算法的噪声免疫力和时间复杂度,证明该方法有更高的噪声免疫力和更低的时间复杂度。特别是,当相邻编码条纹图的条纹数之比不等于2时,正指数条纹序列算法出现严重噪声,而提出的方法依然能够正常工作。此外,该算法还能够根据实际情况决定需要投影的条纹频率,从而能够使用相对较少的条纹编码图像进行有效的相位展开,进而提高系统的实时性。理论分析和实验结果都证明了提出算法的有效性。     

Fringe contrast-based 3D profilometry using fringe projection

Quality-guided algorithm is a widely used method in phase unwrapping. This paper shows an accurate quality map based on fringe contrast for 3D shape measurement. Phase-shifted fringe patterns are projected onto an object surface by a programmable liquid crystal projector and recorded by a CCD camera. A wrapped phase map and a fringe contrast map are extracted from the deformed fringe patterns by the phase-shifting technique. Guided by the contrast map, the quality-guided unwrapping algorithm minimizes unwanted shadow and non-uniform surface reflectance effects and is able to retrieve a correct surface profile. Validity of the proposed method is tested on a fish model and a cutting tool specimen.     

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11.7076和4.9775,新算法的均方根误差则为0.9459,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.     

A novel 3D measuring method for discontinuous object by non-integral twin-frequency grating

A new 3D shape measurement method based on non-integral twin-frequency grating projection is proposed. In this paper, the projected composite grating is composed of two sinusoidal gratings, and the quotient of whose frequencies is not an integer. By using appropriate phase-shifting algorithms, two wrapped phases can be obtained from sixteen frames of the distorted grating patterns. In aid of appropriate phase unwrapping method, the unwrapped phase of high frequency fringe is obtained only from the relation of the two wrapped phases by a pixel-to-pixel phase unwrapping technique. Therefore the unwrapped phase of high frequency fringe pattern is independent of the low frequency fringe pattern, different from traditional integral twin-frequency grating projection methods in which the phase unwrapping error of low frequency fringe pattern may be propagated onto the unwrapped phase of high frequency fringe pattern. The new theory proves that the proposed method is applicable to measure discontinuous object, and has considerable measurement accuracy.     

利用颜色编码辅助计算绝对相位的傅里叶轮廓术

针对传统去卷积算法时间需求的弊端,提出一种新的使用颜色编码辅助的绝对相位并行计算方法。该算法采用对光栅数目需求最少的傅里叶变换轮廓术（FTP）做为卷积相位求取的方法;颜色编码光栅被用来标识轮廓的序数。直接使用FTP计算出的卷积相位以及从彩色光栅中获得的轮廓序数,即可方便求出当前像素的绝对相位值;同时只用一副图像标识轮廓序数也比其他轮廓序数标识方法简单。本方法由于使用绝对相位计算方法,局部相位误差不会扩展。实验结果也证明了此算法对于多个分离物体以及复杂物体的有效性。     

Phase locked loop profilometry

An innovative technique for obtaining automatic three-dimensional shape information of a diffuse surface is presented. The technique is based on a new approach of phase measuring from a fringe pattern. The target to be studied is first modulated by projecting a linear grating onto its surface. The linear fringes are deformed according to the surface shape. Demodulation is carried out by determining the phase of these deformed fringes using a novel digital phase locked loop demodulation algorithm. The technique has the main advantage that the traditional phase unwrapping process is not required. The phase is determined continuously as the algorithm scans the two-dimensional fringe pattern. Owing to its sequential nature, this phase detection technique can be implemented using a special purpose video processor for phase determination at video rates, making it a very fast algorithm. The algorithm along with experimental results of real surface profiles are presented.     

用于三维测量的快速相位解包裹算法

减少条纹投影轮廓术的条纹图数量一直是本领域的研究热点。传统的时间相位解包裹算法,一般需要额外的条纹信息来确定条纹级次,导致条纹图数量过多。提出一种用于三维测量的快速相位解包裹算法,只需要N步标准相移正弦条纹图,就可以完成绝对相位的计算。首先,利用标准相移算法计算包裹相位和消除背景的掩膜;然后,直接利用包裹相位和掩膜,根据连通域标记算法计算条纹级次,进而求得绝对相位。该方法最少只需3幅条纹图,就可以完成三维测量,数据处理速度快。计算机仿真和实验结果验证了该方法的有效性和鲁棒性。     

A novel optical method without phase unwrapping for subsurface flaw detection

This paper presents a novel optical method without phase unwrapping for subsurface flaw detection, based on the computer-vision reflection grating technique. In the setup, a computer-generated fringe pattern displayed on a computer-monitor is placed in front of the test object surface and forms a mirror image behind the reflective surface. The fringe pattern is perturbed according to the surface slope distribution. Unlike the current fringe pattern analysis techniques, which require one/several images, the analysis algorithm of the present method involves a sequence of fringe patterns having multiple frequencies to deduce the ‘pixel-slope’ information which is directly related to the surface slope of the test object. The novel method offers independent analysis for each pixel of the data array, and thus the problem of phase discontinuity in phase unwrapping can be eliminated. In this paper, experimental demonstration of the novel optical method to subsurface flaw detection is presented.     

光弹性测量中的位相展开

根据调制度排序，提出了一个新的用于模型全场光弹条纹级次测量的位相展开方法，并进行了实验验证。在位相展开区域的边界上，位相展开的路径由像素的强度调制决定。这个方法的优点是很明显的，即使在最坏情况下，其误差也限制在局部最小区域上。     

相位锁定循环投影技术及其应用

由一组规则栅线投影到物体表面的变形光栅,采用相位锁定循环解调算法解调出含有物体表面高度信息的相位.该技术的最大优势是不需传统的相位去包裹.利用该算法对二维栅线图扫描确定的相位.本文给出了一个典型试件的实验结果和分析.     

A fast,accurate phase unwrapping method for wavelet-transform profilometry

A novel phase unwrapping method used in wavelet-transform profilometry is presented to improve the accuracy and speed of the unwrapping process. The wrapped phase of the fringe image is extracted by using wavelet transform. How to establish quality map using scale factor at wavelet ridge is discussed firstly. The proposed method can reflect the reliability of the pixels in fringe image effectively. As the consuming time of traditional flood-fill phase unwrapping algorithm is too long, an improved quality-guided method is used in phase unwrapping process. We divide the wrapped phase map into two levels following the established quality map, and process these two levels using different algorithms. Compared with the traditional flood-fill algorithm, we can get the accurate result while the consuming time of the phase unwrapping process is much less by using the proposed method. Simulation and experiment results verify that the 3D information of the measured object can be obtained rapidly and accurately by using the proposed method. Also the dynamic object can be measured too.     

A digital spatial carrier for wavelet phase extraction

In this paper, we present a new method to digitally add a high-frequency spatial carrier in order to use the wavelet phase extraction algorithm, which leads directly to the phase without the unwrapping process. The method needs a fringe pattern and its π/2 shifted version. The application is performed with two shifted fringe patterns obtained from the phase shifting images of the thermomechanical study of an MOS power transistor. A comparison with the phase shifting results is made.     

嵌入式三维数字成像系统

提出一种基于数字信号处理器(DSP)的嵌入式三维数字成像系统设计方案。该方案的硬件平台由条纹投影模块、数据采集模块、条纹自动分析模块及储存器等其他辅助电路组成。条纹投影模块将DSP输出的正弦光栅条纹, 经视频编码后用DLP投射到物体表面; 数据采集模块通过CCD相机采集被物体表面三维信息调制后的变形条纹图, 并进行视频解码; 条纹自动分析模块中利用相移算法计算折叠相位, 再结合相位展开算法求绝对相位分布。系统软件采用多线程技术并行控制三个模块。在相位解调过程中以软件流水线为主综合运用了循环展开、数据预取和内联函数等多种方法优化解调程序。实验结果表明, 该系统可以高速、准确地实现三维轮廓测量,优化后相位展开程序速度是优化前的7倍。     

基于希尔伯特变换的干涉条纹相位解调新算法

提出了一种新的应用希尔伯特变换解调干涉条纹相位的算法,可以从单幅干涉条纹图中解调出全场相位分布.在实际应用中,常借助傅里叶变换实现希尔伯特变换算法,但是会忽略负频率成分,造成相位信息的丢失.对于相位分布非单调变化的干涉条纹,提出了一种判断函数,用来计算相位信息零频率点的分布.利用相位的零频率点分布构造了一个二元模板,使用该模板对本文提出的两次希尔伯特变换法产生的包裹相位图进行修正.对修正后的包裹相位图进行解包裹处理,可以得到连续的全场相位分布.对该方法用计算机模拟进行了验证.