Fringe order error in multifrequency fringe projection phase unwrapping: reason and correction

A multifrequency fringe projection phase unwrapping algorithm (MFPPUA) is important to fringe projection profilometry, especially when a discontinuous object is measured. However, a fringe order error (FOE) may occur when MFPPUA is adopted. An FOE will result in error to the unwrapped phase. Although this kind of phase error does not spread, it brings error to the eventual 3D measurement results. Therefore, an FOE or its adverse influence should be obviated. In this paper, reasons for the occurrence of an FOE are theoretically analyzed and experimentally explored. Methods to correct the phase error caused by an FOE are proposed. Experimental results demonstrate that the proposed methods are valid in eliminating the adverse influence of an FOE.