High-speed three-dimensional absolute shape measurement with three projected binary patterns

Reducing the number of structured patterns for three-dimensional (3-D) reconstruction is of great importance for high-speed 3-D shape measurement. We present a method that reconstructs absolute 3-D shape using three projected binary patterns: one direct current (DC), one low-frequency, and one high-frequency fringe pattern. The procedures are (1) take the difference between the sinusoidal fringe patterns and the DC pattern; (2) apply Hilbert transform to the difference images to generate two phase maps; (3) employ the geometric-constraint-based phase unwrapping method to unwrap the low-frequency phase map; (4) unwrap the high-frequency phase map using the unwrapped low-frequency phase map; and (5) reconstruct 3-D shape. We developed a prototype system that can capture two-dimensional images at 6000 Hz, achieving 2000 Hz 3-D shape measurement speed.