Application of two-dimensional wavelet transform in the modulation measurement profilometry

The vertical optical measurement method with coaxial projection and imaging can measure the complex surface or step-like surface because it helps to avoid the shadow and occlusion. Instead of the phase calculation and phase unwrapping processing, only the modulation information is needed to reconstruct the surface of the tested object by this method. To improve the accuracy of the modulation calculation at each scanning position from only one fringe pattern, this paper introduces the two-dimensional (2-D) wavelet transform into modulation measurement profilometry. The relationship between the 2-D complex wavelet transform coefficients and the modulation distribution of the fringe is deduced. The computer simulation and experiment are carried out to verify that the method based on the 2-D complex wavelet analysis offers higher accuracy than that based on the Fourier transform analysis. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)