Depth range enhancement of binary defocusing technique based on multi-frequency phase merging.

Binary defocusing technique has demonstrated various merits for high-speed and high-accuracy three-dimensional measurement. However, the existence of excessive defocusing zone (EDZ) limits the depth range of binary defocusing system. To overcome this problem, this paper proposes a multi-frequency phase merging (MFPM) approach, which makes it possible to measure the object surface in large depth range (LDR). The method is based on our finding that for different fringe frequencies, the associated EDZs of binary defocusing system are different and not totally overlapped. Thus by merging the phase maps of multiple binary fringes, we could effectively enhance the measurement depth range. Meanwhile, a strategy to determine the optimal combination of fringe frequencies is also proposed by analyzing the phase error distribution under different defocusing degrees. Both simulations and experiments verify the effectiveness and robustness of the proposed method.