基于条纹等值线相关的散斑条纹图处理新方法

在数字散斑干涉术中,通常由物体变形前后得到的两幅原始散斑场用相减方法来得到条纹图,并由相移后的多幅(三幅以上)条纹图来求取相位场。介绍了一种基于条纹等值线相关的条纹图生成新方法,并在此基础上提出了基于单幅干涉条纹图的相位场提取新方法和基于条纹等值线相关的单步相移新方法。实验结果表明,该方法具有良好的结果和发展前景。     

线性相关计算形成数字剪切散斑相关条纹图

本文提出了用线性关计算法形成数字剪切散斑干涉纹的新方法，从理论分析和实验研究均证明，用该方法所获得的数字剪切散斑相关条纹图在图象监视器上易于观盾，条纹图象光强无直流分量影响且可见度较减模式要高，该新方法的采用为今后的条纹图象分析了奠定了基础。     

线性相关计算法形成数字剪切散斑相关条纹图

本文提出了用线性相关计算法形成数字剪切散斑干涉条纹的新方法,从理论分析和实验研究均证明,用该方法所获得的数字剪切散斑相关条纹图在图象监视器上易于观看,条纹图象光强无直流分量影响且可见度较减模式要高,该新方法的采用为今后的条纹图象分析奠定了基础。     

用数字滤波消除散斑条纹图噪声

本文讨论了散斑摄影条纹图的噪声来源及模型,设计合适的数字滤波器.采取正交实验手段,全面分析了噪声、条纹对比度和密度对条纹方向及间距测量精度的影响.     

数字散斑条纹图的滤波方法

在现代数字散斑测量方法中,一般采用减模式来产生数字散斑条纹图,它是进一步图像处理的信息载体,同时不可避免地附带有大量的乘性噪声。为了保证测量精度,在进一步图像处理前必须对其进行降噪,选择合适的滤波方法显得尤为重要。在多年实际经验及阅读了大量文献的基础上,该文对国内外常用的数字散斑干涉条纹图滤波方法进行了分类阐述,选择了一些有代表性的方法予以实现,给出实验结果,并进行了对比分析。最后对数字散斑干涉条纹图滤波方法的发展方向给出了自己的看法。     

基于Gabor滤波的散斑条纹图平滑方法

提出了一种基于伽博(Gabor)滤波的散斑条纹图平滑方法.通过加窗傅里叶运算提取散斑条纹图的条纹频率和条纹梯度方向,并利用它们确定具有频率和方向选择性的Gabor滤波器对散斑条纹图进行Gabor滤波.数值模拟和实验结果表明,该方法在滤除散斑噪声的同时能够有效的保留散斑条纹图的条纹结构,为从单幅散斑条纹图中进一步提取条纹相位场奠定了良好的基础.     

散斑条纹的快速高精度处理技术

本文提出一种快速高精度散斑杨氏条纹(斑纹)场处理方法——同态阀值滤波法。用它实现了散斑场条纹的快速、逐点连续高精度处理。     

数值孔径与数字剪切散斑干涉条纹亮度的关系

分析了数字剪切散斑干涉条纹图的形成理论，并获得了条纹亮度与摄象机数值孔径等参数的精确关系式，从理论分析和实验验证均得出在采用小的摄象机数值孔径和３ｍＷ Ｈｅ－Ｎｅ激光器的情况下，仍可获得比较满意的数字剪切散斑干涉条纹图，理论工作及其结论对于进行数字剪切散斑干涉实验的最佳参数选择具有指导作用。     

散斑错位干涉术条纹的形成与特性分析

通过相关计算及滤波分析,建立了散斑错位干涉术条纹强度的统计分布,从而得到了这类条纹更为一般的特征属性.     

基于统计滤波的单幅散斑条纹图的相位恢复技术

基于统计信号处理技术的贝叶斯（Bayes）估计原理,提出一种新的滤波方法。该方法能有效减少散斑条纹图中的噪声,而且仅用一幅散区斑条纹图就能获得准确的条纹相位分布,通过实例说明了该方法的处理过程。     

Quality assessment of speckle patterns for digital image correlation

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring technique, which is nowadays widely used in the domain of experimental mechanics. The technique is based on a comparison between pictures taken during loading of an object. For an optimal use of the method, the object of interest has to be covered with painted speckles. In the present paper, a comparison is made between three different speckle patterns originated by the same reference speckle pattern. A method is presented for the determination of the speckle size distribution of the speckle patterns, using image morphology. The images of the speckle patterns are numerically deformed based on a finite element simulation. Subsequently, the displacements are measured with DIC-software and compared to the imposed ones. It is shown that the size of the speckles combined with the size of the used pixel subset clearly influences the accuracy of the measured displacements.     

A comparative study of phase-shifting algorithms in digital speckle pattern interferometry

Digital speckle pattern interferometry (DSPI) is a tool for making qualitative as well as quantitative measurements of deformation of objects. Phase-shifting algorithms in DSPI are useful for extracting quantitative deformation data from the system. Comparative studies of the different phase-shifting algorithms in DSPI for object deformation measurement are presented. Static and quasi-dynamic deformation of the object can be measured using these algorithms. Error compensating five-step phase-shifting method is used for the algorithms.     

Development of microscale pattern for digital image correlation up to 1400 °C

Speckle patterns to be used for digital image correlation (DIC) at the micrometer level up to 1400 °C were fabricated by several methods. The quality of the patterns before and after heating was evaluated in terms of the mean intensity gradient (MIG) and the speckle size distribution. The displacement accuracy in simulative translation of images showed that the MIG alone was not enough to evaluate the pattern properties; a large MIG, an even speckle size distribution, and a wide speckle size range pattern were required for a good DIC. The reaction between the patterning material and substrate, the cracking of speckles, and the plastic flow of patterning material may cause changes in the pattern morphology at high temperature. Two patterning methods, spraying a mixture of ceramics powder and binder by a fine-nozzle air brush and abrading a polished surface, yielded a small pattern with high MIG values and even size distributions that was stable at 1400 °C. The potential of the fabricated patterns was shown by measuring the coefficient of thermal expansion of polycrystalline Al₂O₃ from 800 °C to 1400 °C.     

Speckle pattern quality assessment for digital image correlation

To perform digital image correlation (DIC), each image is divided into groups of pixels known as subsets or interrogation cells. Larger interrogation cells allow greater strain precision but reduce the spatial resolution of the data field. As such the spatial resolution and measurement precision of DIC are limited by the resolution of the image. In the paper the relationship between the size and density of speckles within a pattern is presented, identifying that the physical properties of a pattern have a large influence on the measurement precision which can be obtained. These physical properties are often overlooked by pattern assessment criteria which focus on the global image information content. To address this, a robust morphological methodology using edge detection is devised to evaluate the physical properties of different speckle patterns with image resolutions from 23 to 705 pixels/mm. Trends predicted from the pattern property analysis are assessed against simulated deformations identifying how small changes to the application method can result in large changes in measurement precision. An example of the methodology is included to demonstrate that the pattern properties derived from the analysis can be used to indicate pattern quality and hence minimise DIC measurement errors. Experiments are described that were conducted to validate the findings of morphological assessment and the error analysis.     

Evaluation of the 1D empirical mode decomposition method to smooth digital speckle pattern interferometry fringes

The 1D empirical mode decomposition method is applied to reduce speckle noise in the correlation fringes produced in digital speckle pattern interferometry. This method is based on the decomposition of a signal in a sum of well-behaved fast and slow oscillation modes through a sifting process, which generates a fully data-driven technique. Consequently, this is an adaptive approach and the use of basis functions in the analysis process is not required. The denoised signal is given by the residue obtained after the fast oscillation modes are removed. The performance and limitations of the denoising technique are analyzed using computer simulated fringes and these results are compared with those obtained using a wavelet sub-band removal approach. An application of the EMD method to denoise experimental correlation fringes is also presented.     

A simple method of contrast enhancement and extremum extraction for interference fringes

A method of interference fringe processing by finding the average and the extremum gray levels of image points within a fixed or varying window and then computing the modified image intensity with a simple algorithm is proposed. This method can yield a uniform brightness and high (1 or near to 1) contrast at the same time over the whole image area for an input pattern with low contrast and considerable luminance variation, when a relatively large window is used. It can also perform extremum extraction if a small window is employed. This technique is simple, effective and convenient for use, as has been verified by a series of examples of simulated and experimental fringe processing.