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A sequence of image processing algorithms for the analysis of interference patterns generated by a phaseshifting speckle interferometer is discussed. The goal is the accurate determination of displacement and strain components at the surface of an object. The phase change related to the displacement is accurately calculated from eight digitized interference patterns using a phase-shifting algorithm. Digital image processing algorithms have been developed for phase unwrapping, phase restoration, and phase fitting. During the processing steps a binary mask is used to solve the problem of invalid areas. Experimental results for the strain components at the surface of a simple object demonstrate a repeatability of 0.3-microstrain rms.
Vrooman et al. (1991) studied this question.