High-speed three-dimensional shape measurement based on robust Gray-code coding strategies

The measuring technique combining phase-shifting algorithm and Gray-code light has been widely used in three-dimensional (3D) shape measurement for static scenes owing to its high robustness and anti-noise ability. However, it is challenging for this method to realize a high-speed shape measurement using fewer patterns. Because of the object motion and the defocus of the projector, phase unwrapping errors occur easily on the boundaries of adjacent Gray-code words. In existing methods, median filtering or extra patterns projecting were used to overcome this challenge. In this paper, two robust Gray-code coding strategies have been proposed for the same purpose. By recoding the traditional Gray codes in temporal and spatial domains respectively, cyclic complementary Gray-code (CCGC) patterns and shifting Gray-code (SGC) patterns are designed. Both of these two coding strategies can obtain two sets of decoding words whose boundaries are stagger for one wrapped phase. To avoid using the decoding words on the edge, different decoding codes are used depending on the range of phase value. So the robust and simple phase unwrapping can be achieved without projecting extra patterns. High-quality 3D results of multiple randomly moving objects with sharp edges verified the proposed methods' feasibility and validity.