Generating sinusoidal fringe by defocusing: potentials for unprecedentedly high-speed 3-D shape measurement using a DLP projector

This paper presents a technique that reaches 3-D shape measurement speed beyond the digital-light-processing (DLP) projector's projection speed. For this technique, a "solid-state" binary structured pattern is generated with each micromirror pixel always being at one status (ON or OFF). By this means, any time segment of projection can represent the whole signal, thus the exposure time can be shorter than the projection time. A sinusoidal fringe pattern is generated by properly defocusing a binary one, and the Fourier method can be adopted for 3-D shape measurement. We have successfully reached 2000 Hz 3-D shape measurement speed with good measurement quality. Because the fringe pattern is generated digitally, this proposed technique provides an alternative flexible approach for high-speed applications.