Research On The Method Of The Digital Image Correlation Based On Upsampling

Digital Image Correlation(DIC)measurement method can be used to measure the surface displacement of objects.Because of its simple equipment,non-contact measurement,and low environmental requirements,it has become the most active measurement method in academia and industry in photometry.However,many factors such as the selection of algorithms and calculation parameters affect the accuracy of sub-pixel displacement measurement of digital image correlation,and the current sub-pixel displacement measurement accuracy is relatively low,which cannot meet the accuracy requirements of current engineering.Therefore,this article mainly focuses on how to improve the accuracy of sub-pixel displacement measurement of digital speckle correlation methods.This thesis studies the basic theory of digital speckle correlation measurement methods,analyzes the coordinate relationship before and after speckle image deformation,introduces a variety of correlation coefficient criteria,and establishes a mathematical model for sub-pixel displacement measurement,mainly including gray interpolation method and surface fitting method,and a variety of common interpolation algorithms are summarized.The use of higher-order interpolation algorithms in the traditional gray-scale interpolation method cannot further improve the accuracy of sub-pixel displacement measurement.Therefore,this article will study the digital image correlation measurement method based on upsampling.This thesis proposes an interpolation method combining upsampling and B-spline interpolation.Firstly,analyze the basic principles of upsampling in the field of digital signal processing,and separately derive the implementation process of increasing the signal sampling rate in the digital domain from the time and frequency domain perspectives.Then,the window design method of anti-image interpolation digital filter is given.Secondly,based on the results of up-sampling processing sequence of data points can only be a multiple of interpolation,then B-spline interpolation in order to achieve an arbitrary sequence of data points interpolation.Finally,in order to verify the effectiveness of the proposed interpolation method,an interpolation simulation experiment is performed on the computer-simulated one-dimensional test sequence.The results show that the interpolation method combining upsampling and B-spline interpolation has higher interpolation accuracy than the method using only B-spline interpolation.In this thesis,an interpolation method combining upsampling and B-spline interpolation is proposed as a method for digital speckle displacement measurement.Firstly,for the interpolation module,the realization steps of two-dimensional upsampling processing are given,the spectrum of the digital speckle image is analyzed,and the relevant parameters of the anti-mirror interpolation digital filter are fixed.Secondly,for the displacement positioning algorithm module,analyze and derive two mainstream non-linear iterative algorithms in DIC:forward additive Gauss-Newton and inverse compositional Gauss-Newton,and determine the overall process of sub-pixel displacement measurement based on upsampling using these two algorithms.After that,the above one-dimensional test sequence was used to perform simulation experiments.The results show that the interpolation method combining upsampling and B-spline interpolation has better displacement measurement accuracy than the method using only B-spline interpolation.Finally,for the computer-simulated and real two-dimensional digital speckle images,the zero-mean normalized least squares correlation criterion is used to give a comparison of the measurement accuracy of displacement from the perspective of displacement mean bias error,standard deviation and root mean square error.The simulation results show that the digital image correlation method based on upsampling can significantly reduce the error caused by interpolation,and ensure the stability of the standard deviation,improve the displacement measurement accuracy of the digital image correlation method,and meet the stability and high precision requirements of displacement measurement of object deformation field.