Recovery of absolute height from wrapped phase maps for fringe projection profilometry

A novel multi-frequency fringe projection profilometry is presented in this paper. Fringe patterns with multiple frequencies are projected onto an object by a digital micro-mirror device projector. The approach involves an improved Fourier transform profilometry method with an additional π phase shifting stage and hence the acquisition of two source images. A peak searching algorithm is then employed to obtain the real height profile of the object together with a mathematical proof of this algorithm. In our method, the height of each point on the object is measured independently and the phase unwrapping procedure is avoided, enabling the measurement of objects with large depth discontinuities, where the phase unwrapping is difficult. The measurement result is given to validate the method in the paper. Our technique has great potential in industrial applications where the measurement of objects with complex shape and large discontinuities is needed.