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.

Fourier transform profilometry is one of the popular non-contact 3-D measurementmethods, where a Ronchi grating or sinusoidalgrating is projected onto a diffuse threedimensionalsurface,and the resulting deformed grating image is detected by a CCD cameraand processed by a computer. This method requires only one frame (or two frames) of thedeformed fringe pattern in some algorithms to retrieve the surface of measured object, so it hasobvious advantage for realtime data acquisition and 3-D measurement of dynamic process. Inthis paper, we review some algorithms in FTP, discuss some important problems, includingfrequency spectra overlapping, phase unwrapping, sampling, and 3-D measurement ofdynamic process. With the development of computer hardware and software and availabilityof high-resolution image grabber, FTP method will be a promising one for acquiring 3-D dataof object, and more and more researchers pay attention to it.