High-speed 3D shape measurement using efficient moire-assisted three-frequency heterodyne phase unwrapping algorithm

The conventional three-frequency heterodyne phase unwrapping (CTHPU) algorithm works very well in mea-suring isolated objects or discontinuous surfaces. However, it is unsuitable for high-speed applications due to many exposures to reconstruct one 3D profile. To this end, we propose a moire-assisted three-frequency het-erodyne phase unwrapping (MTHPU) algorithm, in which only four fringe patterns are needed to be projected to update one 3D result in dynamic scenes. In the proposed method, the wrapped phase distributions of the highest-frequency fringe patterns are calculated by three-step phase-shifting technique to ensure accuracy. And, the heterodyne phase maps, which are used to fulfill the absolute phase unwrapping, are extracted by a novel complex computational moire algorithm from the other two fringe patterns and the highest-frequency wrapped phase. Moreover, the number of exposures can be further reduced to four to produce a 3D measurement by multi-plexing the projecting sequence. Therefore, the proposed MTHPU can achieve high accuracy and high-efficiency measurement in dynamic scenes. Experiments demonstrate that our method can achieve a high 3D reconstruction frame rate of 2381 Hz.