Automatic Selection Method for Parameters of Bandpass Filter in Fourier Transformation Profilometry

The digital bandpass filter in frequency domain plays a key role in Fourier transformation profilometry (FTP). Considering the variations of optical geometry and relevant parameters in FTP, an automatic selection method for parameters of bandpass filter in FTP is presented in this paper. In the proposed method, with only one frame of deformed fringe pattern, numerical differentiation is applied to the Fourier frequency spectrum of the deformed fringe pattern in FTP, in order to find roughly the initial center position of base frequency; next, image histogram and threshold segmentation techniques are used to process the Fourier frequency spectrum to automatically and accurately obtain the center frequency and bandwidth of the bandpass filter, so to realize the automatic processing of frequency filtering. The proposed method can automatically adapt to the variations of optical geometry and relevant parameters in FTP, can make the FTP produce its advantage in dynamic measure, and it will find wide application in engineering. Computer simulation and experimental results with real data show the validity of the proposed method.