Shape defect measurement by fringe projection profilometry and phase-shifting algorithms

We propose a fringe-projection profilometry technique for shape defects measurement, which can be employed for three-dimensional (3-D) quality inspection. The proposal consists of using a template surface to design phase-shifting algorithms with special-purpose phase response via the frequency transfer function. These algorithms can jointly and directly estimate the spatial phase deviations in a 3-D inspection. Phase deviations correspond to shape differences between the template shape and a testing one. The phase-unwrapping procedure is unnecessary when phase differences are small, as is usual in quality inspections. Experimental results show that our technique is so sensitive that the ripples in a fingerprint can be retrieved.