Y. Wang, C. Jiang, and S. Zhang, "Double-pattern triangular pulse width modulation technique for high-accuracy high-speed 3D shape measurement," Opt. Express 25(24), 30177-30188 (2017); doi:10.1364/OE.25.03177
Using 1-bit binary patterns for 3D shape measurement has been demonstrated advantageous over using 8-bit sinusoidal patterns in terms of achievable speeds. However, the phase quality generated by binary pattern(s) typically is not high if only a small number of phase-shifted patterns is used. This paper proposes a method to improve the phase quality by representing each pattern with the difference of two binary patterns: the first binary pattern is generated by triangular pulse width modulation (TPWM) technique, and the second being $\pi$ shifted from the first pattern is also generated by TPWM technique. The phase is retrieved by applying a three-step phase-shifting algorithm to the difference patterns. Through optimizing the modulation frequency of the triangular carrier signal, we demonstrate that high-quality phase can be generated for a wide range of fringe periods (e.g., from 18 to 1140 pixels) with only six binary patterns. Since only 1-bit binary patterns are required for 3D shape measurement, this paper will present a real-time 3D shape measurement system that can achieve 30 Hz.