The Optimized Design And Error Analysis Of Digital Speckle Patterns

Because of advantages of non-contact,full-field,and low environmental requirements,digital image correlation is increasingly used in civil,mechanical,biological,aerospace and other industries.The method is based on tracing the texture pattern features on the surface of the test piece to measure the appearance,movement and deformation of the test piece.Therefore,the speckle patterns on the surface of the specimen is crucial to the digital image correlation method.At present,there is still no conclusion on how to make a speckle patterns on the surface of the specimen,and what kind of speckle patterns is produced.This leads to different results for different experimenters in the same experiment,which makes the correctness has been questioned,and greatly limiting the application of digital image correlation methods.To solve this problem,we need to find a stable and high-quality speckle patterns.The speckle patterns should correspond to the smallest calculation error of digital image correlation method.In order to find this speckle field,this paper firstly analyzes the 36 speckle patterns used by our group in experiments.The best speckle pattern in the 36 speckle images is given by analog digital image correlation calculation,and the reason for the small calculation error of the digital image correlation method is analyzed.Further analysis confirms that it is hard to fully evaluate the quality of the speckle field using the mean intensity gradient,and the description descriptors,the smoothness descriptors,and the variance descriptors described in the image processing discipline are highly correlated with the calculation error of the digital image correlation method.However,in order to obtain the optimal speckle field,it is not sufficient to statistically analyze the existing speckle pattern.Theoretical analysis is also needed.For this reason,this paper summarizes the theoretical relationship between the various parameters of the speckle field and the calculation errors of the digital image correlation method.Then,using the branch-and-bound method to obtain the speckle patterns with the largest intensity gradient in the sub-region under certain conditions.Comparing with the random pattern which each pixel has 50% probability to be black,the root mean square error(RMSE)reduces by 40% approximately,and the MIG used prewitte operator increases by about 60%.The a convenient and practical method of designing digital speckle patterns based on point distribution are also given.The accuracy is higher than the speckle field calculated by the optimization method.At the end of this article,the feasibility and superiority of optimizing the speckle patterns were verified in two practical experiments.In this paper,the design of digital speckle patterns in digital image correlation method is deeply studied.Through theoretical analysis and experimental research,digital speckle field with higher quality and more stable digital image calculation error is obtained and used.In the actual measurement,the consistency of the speckle patterns in the digital image correlation method is ensured,which provides a reliable means for practical experiments and has a good application prospect.