Improved Double N-Step Phase Shift Method(DNPSM) Based on Unwrapping Before Fusion

In the field of fringe projection profile, the DNPSM becomes a research hotspot because of its small phase error and high detection accuracy. However, the DNPSM is affected by periodic phase error(PPE) in the wrapped phase fusion process, and it produces spurious tones at the edge position of the wrapped phase. To solve this problem, this paper proposes an improved DNPSM based on unwrapping before fusion. Firstly, we get wrapped phase from the two sets of phase shift fringe images(PSFI) captured by camera, and then we unwrap the two groups of wrapped phase with the phase unwrapping method. Finally, we fuse the two unwrapped phase. We use the proposed method compared with complementary Gray code(CGC) N-step phase shift method(NPSM) and CGC-DNPSM that wrapping after fusing respectively. Experimental results show our method could effectively eliminate spurious tones in phase and improve the detection accuracy.