Color phase order coding and interleaved phase unwrapping for three-dimensional shape measurement with few projected pattern

Fringe projection profilometry (FPP) is widely used in 3D measurement of static scenes due to its high precision and contactless. Phase unwrapping is the key step of FPP, which converts wrapped phase into the absolute phase. However, the traditional temporal phase unwrapping (TPU) faces the limitation of a large number of projections and produces periodic errors, which affects the speed and accuracy of the 3D measurement. To address that, we propose a color phase order coding (CPOC) and an interleaved phase unwrapping method (IPU). Firstly, the proposed CPOC method can globally encode 36 periodic stripes using only two patterns, which considerably improves the coding efficiency. Subsequently, an IPU method is proposed to bypass the adverse effects of edge errors. Using the initial wrapped phase, additional three wrapped phases can be constructed, and the phase unwrapping region can be delineated by locating the jump edges of the four wrapped phases followed by phase unwrapping. Since the unstable jump region of the wrapped phase and the incorrect phase order information is not utilized in our approach, the effects of phase order and wrapped phase jump errors are avoided. Experimental results show that our method considerably reduces the number of projected stripes without affecting the measurement accuracy as compared to the conventional TPU method. The results also ascertain the versatility and robustness of the proposed method in complex measurement environments.