Research on ESPI Image Filtering Method Based on Improved Wavelet Thresholding

Electronic Speckle Pattern Interferometry (ESPI) is an optical non-destructive measurement technique. The ESPI streak map contains a large amount of scattering noise, which seriously affects the accuracy of phase information extraction. Aiming at the characteristics of ESPI streak map, this paper proposes an improved wavelet threshold function and adaptive threshold filtering algorithm. The threshold function can effectively overcome the discontinuity and the existence of constant deviation of the hard and soft threshold functions, and the proposed adaptive threshold can effectively inhibit the over-filtering of the effective signal by the traditional fixed threshold. Simulation results show that the improved algorithm improves the peak signal-to-noise ratio by an average of 1.82 dB and the average structural similarity by an average of 11.39% compared with the conventional wavelet hard and soft thresholding method, which can effectively remove the noise of the ESPI image, better retain the fringe detail information of the fringe map, and lay a solid foundation for the subsequent accurate extraction of the skeleton line and phase information.