Binarized dual phase-shifting method for high-quality 3D shape measurement.

Abstract

It has been demonstrated that using 1-bit binary patterns is better than using 8-bit sinusoidal patterns for high-speed applications. However, the phase quality generated from binary patterns is lower, especially when the projector is nearly focused. A dual phase-shifting method can effectively reduce the dominant periodical phase errors caused by high-order harmonics. Yet, such method requires an additional set of phase-shifting patterns, which thus slows down the measurement speed. To overcome this problem, this paper proposes a binarized dual phase-shifting method (BDPS) to generate a high-quality phase map using just three phase-shifted binary patterns. The basic idea is to merge the two sets of squared binary phase-shifting patterns into one set of patterns with three gray levels, which is further binarized by employing 2D area modulation. Given this, the BDPS method can realize error reduction for the binary defocusing technique while maintaining its speed advantage by neither adding the total number of patterns nor the number of bits. The effectiveness of the proposed method is verified by both a quantitative evaluation by measuring a white flat board and an additional quantitative evaluation by measuring a complex sculpture surface.