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.

An automated measurement method for 3600 surface topography of 3-D diffuse objects is presented. The method is based on the simple principle of triangulation with structured illumination. The geometric specifications of the structured light module used in the system are analyzed on a computer. U siIlg aFl advantageous data acquisition schedule, high data acq uisition rates and measuring accuracy can be achieved. The. system comprises a structured lighting projector, a 2-D detector array, and a m icrocomputer for contr01 And processing. Experimental results for 3-D objects are offered.

A new method is presented for automatic phase measuring profilometry (PMP), in which a defocused image of the projected square-wave Ronchi grating and a phase shifting technique are chosen for the optical phase cvatuation. This. makes it possible to design all-electronic LCTV-based PMP systems. In this paper a detailed analysis of the applied phase evaluation algorithm as function of the number of steps, N, is given. The alternating feature of the phase measurement precision e (N), which lead to the obvious choice of seven or five steps, is dearly demonstrated. Then an analytical description is presented of the low.pass optical filtering performed by defocused imaging of the projected and video-frame-grabbed Ronchi grating. It is followed by an analytical description ofthe additional low-pass digital filtering of the same signal due to the inhercnt properties of the N-step phase shifting algorithm. The figure of merits are estimated in comparison to the simulated perfect imaging ofa sinusoidal grating. The results are verified, experimentally by a relief determination of a typical object. For lhis purpose the flve accurately.; b.ifted defocused projections of the original Ronchi grating, spread over the object, were captured by a CCD based video-digitizin3 system and evaluated with a PC.