Spatial phase-shifting profilometry by use of polarization for measuring 3D shapes of metal objects

In this paper, we present a polarization spatial phase-shifting method for fringe projection profilometry. It enables us to measure the three-dimensional shape of a metal object in a fast way requiring only a single-shot implementation. With this method, a couple of projectors are equipped, in front of their lens, with linear polarization filters having orthogonal polarization directions, so that they can simultaneously cast two sinusoidal fringe patterns having different phase shifts onto the measured metal surfaces without mixture. To register the two projected patterns, we suggest a fringe alignment method based on the epipolar geometry between the projectors. By taking advantage of the property of metal surfaces in maintaining polarization state of incident light, the deformed fringe patterns on the measured surfaces are captured by using two coaxially-arranged polarization cameras. As a result, the fringe phases are calculated by using a two-step phase-shifting algorithm and further the 3D shapes of the measured surfaces are reconstructed. Experimental results demonstrate the proposed method to be valid and efficient in measuring metal objects.