ESPI correlogram analysis by two stage application of wavelet transform with use of intensity thresholding

Abstract

The presented paper deals with the data processing of correlograms acquired by an electronic speckle pattern interferometry (ESPI). Correlograms are highly noised by the speckle pattern and special care should be taken to denoise these correlograms before calculating the demanded phase map or phase profile. This paper presents a process that utilizes two stage use of wavelet transform (WT) for both denoising and a phase profile retrieval. In the first stage the correlogram is denoised by thresholding of wavelet transform coefficients. Unlike the common use, WT phase retrieval process is not directly applied to the denoised correlogram, but rather to its intensity thresholded image, which is done in the second stage. Proposed algorithm is verified by its application to the artificially generated correlograms and in the final step also to the experimentally acquired correlograms.