Profilometry without phase unwrapping using multi-frequency and four-step phase-shift sinusoidal fringe projection.

A three-dimensional (3D) profilometry method without phase unwrapping is proposed. The key factors of the proposed profilometry are the use of composite projection of multi-frequency and four-step phase-shift sinusoidal fringes and its geometric analysis, which enable the proposed method to extract the depth information of even largely separated discontinuous objects as well as lumped continuous objects. In particular, the geometric analysis of the multi-frequency sinusoidal fringe projection identifies the shape and position of target objects in absolute coordinate system. In the paper, the depth extraction resolution of the proposed method is analyzed and experimental results are presented.