High-speed LED array grayscale modulation method for three-dimensional profilometry with defocused projection

Phase-Shifting Fringe Projection Profilometry is widely used for 3D measurements by projecting sinusoidal fringes onto the object and retrieving height information from the distorted fringes. DMD-based projectors face inherent limitations in balancing grayscale level with projection speed. Compared to grayscale projection, the binary defocusing projection significantly improves measurement speed by projecting and defocusing binary fringe patterns to approximate ideal sinusoidal fringes, but it suffers from substantial higher-order harmonics in near-focal area, leading to compromised measurement accuracy. Existing grayscale modulation methods, despite improving sinusoidal quality, remain constrained by the fundamental speed limitations imposed by DMD hardware and display mechanisms, making 3D measurements challenging to achieve both high speed and high accuracy simultaneously. In this paper, we employ a self-developed 128 × 128 high-speed LED array with a maximum refresh rate of 25 MHz for binary fringe patterns, resulting in a 1000-fold speed enhancement over DMD. Meanwhile, we propose a grayscale modulation method specifically optimized for the LED array. The maximum refresh rate for displaying grayscale patterns can reach 6.25 MHz. As a result, the proposed grayscale modulation method significantly improves measurement accuracy by 73.2 % compared to the binary method, thus the effective depth range is consequently enhanced. Our proposed high-speed LED array grayscale modulation method can provide a new solution for achieving high-speed, high-accuracy 3D measurements.