| Digital image correlation(DIC)has been widely used in civil transportation,aerospace and other fields.However,the hardware level such as transmission bandwidth limits the sampling rate of imaging equipment and the transmission requirements of deformation field in DIC.Due to the limitation of sampling rate,high-speed cameras cannot obtain high spatio-temporal resolution images.How to solve the contradiction between temporal and spatial resolution of camera and realize high-precision deformation measurement with high temporal resolution is a problem worthy of research.In addition,the continuous improvement of DIC computing efficiency stimulates the new demand for real-time transmission of deformation field.Due to the limitation of transmission bandwidth,the size of deformation field data must be considered to ensure the stability of transmission.In order to alleviate the pressure of sampling and transmission,this paper combines the idea of"compression"with these two aspects.Compressive sensing and displacement field compression in DIC are studied in this work.In order to improve the frame rate without losing camera resolution,snapshot compressive imaging(SCI)system is introduced into DIC measurement,and the SCI-DIC system is established.The measurement accuracy of the system is closely related to the quality of image reconstruction.However,at present,SCI reconstruction algorithms are generally designed for natural images.In order to further improve the restoration accuracy,Sp-De SCI algorithm specially designed for speckle reconstruction is proposed in this paper.On the basis of De SCI,Sp-De SCI combines normalize sum squared difference(NSSD)correlation function,speckle adaptive block search strategy,adaptive block search window size,adaptive signal aggregation based on correlation coefficient and inverse compositional matching strategy and gauss-newton algorithm(IC-GN).Simulation and real SCI-DIC experiments show that Sp-De SCI has the highest recovery accuracy compared with other advanced SCI algorithms,and its reconstructed frame and displacement field are closest to the true value.Compared with De SCI,which has the highest restoration accuracy at present,the DIC average displacement error of Sp-De SCI is reduced by 0.02 pixel and 0.01 pixel in simulation and real experiments respectively.In order to solve the problem of real-time transmission of displacement field in DIC,two displacement field compression methods based on discrete cosine transform(DCT)and discrete wavelet transform(DWT)are proposed in this paper.For floating-point displacement field data,non-integer and integer quantization for floating-point compression are proposed,and the selection of coding method,filter and filtering mode in JPEG and JPEG2000 are studied.In the laboratory experiment,the recommended parameters based on DCT and DWT compression algorithms are given.The compression ratio of the two algorithms and the calculation time before and after parallel are compared.It is found that the compression performance and calculation efficiency of the former are better than the latter.In the out-of-plane collapse of filled wall field experiment,the compression ratio,average error and calculation efficiency based on DCT method are verified,and the relationship between compression ratio and failure form is analyzed.Overall,it is found that the compression ratio based on DCT method is basically less than 10%,and the parallel computing speed reaches 2.0×10~6 points per second,which can meet the real-time transmission requirement of DIC displacement field based on heterogeneous parallel.This DIC has the highest computational efficiency at present(the computing speed is 1.6×10~6 points per second). |
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