Absolute phase retrieval based on De Bruijn sequence coding

Temporal phase unwrapping effectively overcomes the error propagation issue inherent in spatial phase unwrapping by projecting additional coded patterns to record fringe orders, which is of great significance for achieving high-precision 3D reconstruction in fringe projection profilometry (FPP). To balance phase unwrapping accuracy and measurement efficiency, this paper applies the De Bruijn sequence coding method to the phase unwrapping process of FPP and proposes a novel phase coding method that requires no additional projected patterns. Leveraging the window uniqueness of the De Bruijn sequence, the proposed method first simplifies and maps a 3-bit binary De Bruijn subsequence into a single binary grayscale image to record the fringe orders. Subsequently, by adjusting the grayscale distribution of the projected sinusoidal fringe patterns, the monotonicity of the wrapped phase calculated from the sinusoidal fringes is made to strictly correspond with the binary grayscale image, thereby realizing the transformation from grayscale coding to phase coding. Without increasing the total number of projected fringe patterns, the proposed method achieves the synchronous recording of the phase and its corresponding fringe orders merely by altering the grayscale distribution of the projected fringes. This provides robust technical support for high-precision and high-efficiency phase unwrapping. Both computer simulations and physical experiments have verified the effectiveness of the proposed method.