Phase-shifting coding method for absolute phase retrieval

Abstract

Absolute phase retrieval has been widely studied, as it is not much influenced by the discontinuity and occlusion of objects in phase-measuring profilometry. In the practical measurement, however, fringe order determination is by no means easy when the grayscale of deformed patterns is degraded because of uneven reflectivity or the large curvature of measured objects. We introduce a phase-shifting coding (PSC) method to overcome that problem. In the PSC method, fringe order is encoded by the phase-shifting amounts of additional fringe patterns, and the decoding algorithm to retrieve absolute phase is designed on the basis of phase difference and neighborhood consistency. The special statistical filtering and self-correcting filtering methods are utilized to eliminate absolute phase errors. Experiment results demonstrate that the proposed PSC method is effective and has strong robustness in grayscale degradation regions.