Spatial Quasi-phase-shifting Technique For Fringe Projection Profilometry

Fringe projection profilometry is widely employed in science and engineering. It is an optical measure technique that achieves the three-dimensional information extraction by the analysis of the two-dimensional deformed fringe pattern on the surface of the object. The fringe analysis algorithm is the core technique of this method. It is used to demodulate phase from the deformed fringe pattern.Three-step spatial quasi-phase-shifting algorithm is able to demodulate the phase from a single frame of fringe pattern. The algorithm is suitable for dynamic fringe analysis. On this basis, an improved three-step spatial quasi-phase-shifting algorithm is presented in this paper. According to actual situation, the number of pixels and the size of neighborhood are able to be tuned arbitrarily to calculate the phase of each pixel. It is conducive to the noise isolation, the error-propagation prevention, and accuracy improvement in phase demodulation for fringe analysis.In order to avoid calculating the local frequency and to improve the accuracy, a four-step spatial quasi-phase-shifting algorithm is presented. It is based on the three-step algorithm to simplify the formula. It is a compact single-frame algorithm using the integral fringe intensities demodulates the phase but without the local frequency detection process. Because the modulated phase can be represented by the intensities, it is more suitable for dynamic fringe projection profilometry in term of the accuracy of the phase demodulation.Finally, it has been demonstrated by experiments that the result is precise by using the improved three-step algorithm and the four-step algorithm, respectively. In addition, we carried out a dynamic profilometry using the proposed four-step algorithm.