Inner Shifting-Phase Method for High-Speed High-Resolution 3-D Measurement

Fringe projection profilometry (FPP) is widely used in the 3-D noncontact measurement. In FPP, one of the most important steps is obtaining the absolute phase through fringe orders and wrapped phase. The existing methods usually acquire the fringe orders and wrapped phase independently. Therefore, more patterns are needed to project onto the object, which decreases the measuring speed a lot. We propose an inner shifting-phase method that codes the fringe orders and the wrapped phase into the same four patterns. With the unwrapping algorithm, we obtain the fringe orders and the wrapped phase simultaneously, which decreases the number of required patterns a lot. The proposed method calculates the absolute phase pixel-by-pixel independently without any preacquired information or geometric constraints. Experiment results show that the proposed method achieves almost the same accuracy with only a third of the patterns required by the conventional three-frequency four-step method. Experiment results also verify the validity of the proposed method in measuring both complex and separated objects.