Elimination of nonlinearity in modulation measurement profilometry by Wavelet Transform

Modulation measurement profilometry applies coaxial and coimage plane optical systems to reconstruct the surface shape of the measured object, in which, the direction of the grating projection is the same as that of CCD to capture the images. This technology completes the reconstruction by the extraction of modulation values instead of phase information. It can effectively avoid the shadows, shutoff and calculation of phase unwrapping and accomplish the shape measurement for object with complex surface. However, in the practical application, the measurement precision is usually affected by the nonlinearity of CCD's photoelectric response. In order to avoid the influence of high-order harmonics on fundamental spectrum, Wavelet Transform is introduced into fringe analysis and modulation extraction. With the merits of local analysis and multi-resolution, this method can obtain higher measurement precision by comparing with the Fourier transform method. Both computer simulation and practical experiment testified the validity of the proposed method.