Improved spatial-shifting two-wavelength algorithm for 3D shape measurement with a look-up table

Abstract

Conventional two-wavelength algorithms have been broadly used for three-dimensional shape measurement. However, the maximum unambiguous range of phase unwrapping depends on the least-common multiple of two wavelengths, and thus coprime wavelengths are commonly selected. The recently proposed spatial-shifting two-wavelength (SSTW) algorithm can achieve the maximum unambiguous range with two non-coprime wavelengths, but this algorithm tends to fail for some wavelength selections. To address this problem, this paper presents a general look-up-table-based SSTW (LUT-SSTW) algorithm with arbitrary wavelength selection. The paper also analyzes the phase unwrapping robustness in terms of phase errors and provides guidance for wavelength selection. In addition, an improved LUT-SSTW algorithm is developed to enhance the phase unwrapping robustness, and further relax wavelength selection. Some experiments have been conducted, and their results verify the efficiency of the proposed method.