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.

By using a defocused optical field with a Ronchi grating to get a quasi-sine optical field and by using a grating π phase shifting technique, the fundamental spectrum modulated by the object height distribution can theoretically be eXtended from O to 2fo (fo is the carrier frequency of the optical field) without overlapping the zero component and other higher spectra. Consequently, the measurable slope of height variation can be extended to nearly three times that of the unimproved Fourier transform profilometry method. This paper gives the theory and experiment resplts of the improved Fourier transform profilometry.