Absolute three-dimensional shape measurement with two-frequency square binary patterns

This paper presents a novel method to achieve absolute three-dimensional shape measurement solely using square binary patterns. This method uses six patterns: three low-frequency phase-shifted patterns and three phase-shifted high-frequency patterns. The phase obtained from the low-frequency phase temporally unwraps the phase obtained from high-frequency patterns. The projector is defocused such that the high-frequency patterns produce a high-quality phase, but the phase retrieved from low-frequency patterns has a large harmonic error that fails the two-frequency temporal phase unwrapping process. In this paper, we develop a computational framework to address the challenge. The proposed computational framework includes four major approaches to alleviate the harmonic error problem: (i) use more than one period of low-frequency patterns enabled by a geometric constraint-based phase unwrapping method; (ii) artificially apply a large Gaussian filter to low-frequency patterns before phase computation; (iii) create an error lookup table to compensate for harmonic error; and (iv) develop a boundary error correction method to alleviate problems associated with filtering. Both simulation and experimental results demonstrated the success of the proposed method.