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.