Correction of phase errors introduced by nonlinearity and specular reflection based on double N -step phase-shifting profilometry

The N -step phase-shifting profilometry (PSP) is widely used to calculate the wrapped phases of static objects. However, measurement accuracy and precision can be affected by nonlinear error caused by system nonlinearity, as well as phase error resulting from overexposed regions on objects with highly reflective surfaces. To address these two issues, the phase error due to system nonlinearity and the phase error due to intensity saturation region are analyzed separately in this paper. This paper proposes introducing an additional set of fringe sequences with a π /N phase shift on top of the N-step PSP by fusing the unwrapped phase of the original fringe sequences with that of the additional fringe sequences, i.e., double N -step PSP, in order to suppress the nonlinear error and the error in overexposed regions. The experimental results demonstrate that the double N -step PSP can suppress not only the nonlinear error within the system, but also the error caused by the overexposed regions of the objects with high reflective surfaces.