Application of S-transform profilometry in eliminating nonlinearity in fringe pattern

摘要

The S-transform, conceptually viewed as an extension of the short-time Fourier transform and the wavelet transform, features a time-frequency representation known for its local spectral property and multiresolution strategy. It has been introduced in optical three-dimensional shape measurement based on a fringe projection technique recently. In this paper, an application of S-transform for demo- dulating fringe patterns affected by the nonlinearity has been discussed. Two methods based on the S-transform, called S-transform ridge method and S-transform filtering method, are used to eliminate the phase errors caused by nonlinear factors of the projector and CCD camera. The theoretical repre- sentations of S-transform ridge method and S-transform filtering method in fringe analysis are given. The computer simulation and experiment are carried out to verify our research. Compared with the re- constructions of the windowed Fourier transform, the wavelet transform and the S-transform ridge meth- od, the S-transform filtering method gives a better result under considering the influence of the fringe nonlinearity.