Absolute phase monotonicity guided regional fringe projection 3D imaging

Fringe projection profilometry (FPP) has become one of the most widely used optical reconstruction methods due to its non-contact, high precision, and high speed advantages. However, in the measurement process of some concave scenes in real life, there will be interreflection between different areas. The interreflection inside scenes will lead to incorrect decoding of the projected fringe patterns, and therefore cause 3D measurement errors. In this paper, we propose a regional fringe projection 3D imaging approach guided by absolute phase monotonicity to handle the above mentioned concave scenes with interreflection. The correct absolute phase exhibits a monotonic property, which serves as a crucial intermediate result in the FPP method. By calculating the gradient and its direction of the initial absolute phase, they can effectively guide the segmentation process and fundamentally avoid the problem of interreflections. We have conducted several real experiments corresponding to different typical concave scenes to demonstrate the feasibility and effectiveness of the proposed method. The root mean square error and standard deviation of the proposed method can reach 0.0041 mm and 0.0031 mm, which is an order of magnitude lower than that of the XOR gray code method. And our method requires no additional equipment and is easy to operate, which is practical.