A new method for phase-stepping grating profilometry of complex objects is proposed and verified by experiments. Both, the discrete phase distribution and the modulation depth distribution are calculated. To construct binary control masks the discrete values and the histogram of the modulation intensities are inspected first. Then the blocking lines, which are connecting the pairs of opposite poles. are traced down through the local minimums of the odulation uintensties. The control masks are used to identify valid and invalid discrete phase distributions during phase unwrapping and phase interpolaton, and to control the path of phase unwrapping. The method could equally well be used in grating Profilmetry of in interferometry.

A new phase unwrapping algorithm based on fringe frequencyanalysis in Fourier-transform profilometry (FTP) is presented. Itsframework consists of digital weighted filtering and modulation ordering.By the frequency-weighted filtering, the analysis of fringe frequency isconverted into the analysis of fringe modulation. And based on orderingthis filtered fringe modulation, a more optimized phase unwrapping pathcan be found. When this new algorithm is applied to FTP, the consequentphase unwrapping path is always in the direction from an area inwhich the local spatial frequency is closer to the fundamental frequencyto one in which it is further. Because of the strong correlation betweenlocal spatial frequency and the reliability of phase data, this unwrappingpath also leads from higher to lower reliability. The experiment showsthat the new phase unwrapping algorithm based on fringe frequency isreasonable and effective. Even in the worst case, the error if any, islimited to local-minimum areas.