Hybrid algorithm to reconstruct out-of-plane surface deformations from interferometric image data

摘要

Abstract: Interferometric methods are of particular interest in industrial quality assurance to detect material defects via deformation and vibration analysis. One of their main advantages is contact-free surface examination and the possibility to provide full-field information with sub-micron sensitivity. When examining intensity images provided by a phase-shifting speckle interferometer, the measuring range is limited because the phase wrapping effect occurs in combination with high speckle noise levels. In this paper, a new hybrid approach for the phase unwrapping problem is presented which significantly extends the measuring range, and, in addition, reduces the computational effort. This is achieved by a specific tile processing strategy combining a polynomial based local phase-unwrapping approach and a Fourier based strategy to form a hybrid algorithm. The hybrid approach assures time efficient tile processing using polynomial approximation in image areas of low fringe density on the one hand and carefully directed high performance slope computations in noisy or strongly deformed areas on the other hand. In these strongly deformed areas a Fourier based approach can still find the correct affine linear approximation. With the resulting set of local affine linear approximations, a global spline model of the underlying deformation profile is obtained by an iterative region-growing technique combined with a O(n) data transformation. !7