SLBL-PU: Shadow-Based Layer-By-Layer Phase Unwrapping for Efficient 3D Measurement

Phase-shifting (PS) based structured light technology shows excellent 3D perception performance. However, it requires projecting a extensive array of patterns, imposing constraints on the measurement space, or embedding additional signals for phase unwrapping (PU), leading to motion artifacts and low robustness. To surmount these challenges, we propose a shadow-based, layer-by-layer phase unwrapping (SLBL-PU) method, which enables absolute phase recovery for deep objects without the need for any supplementary patterns. In the initial phase, attention is focused on a novel truncation feature within the local phase, facilitating the use of iterative PUs to derive the modulated phase. Inspired by shading theory, in the second phase, the absolute phase is restored based on the geometric relationship between the imaging system and the object shadows. Additionally, by incorporating a time-division multiplexing strategy, the efficiency of 3D reconstruction in dynamic scenes is further tripled. In experiments involving different depths, phase modulation, complex colored, and dynamic scenes, the proposed method demonstrated superior performance. Specifically, in static environments (0 mm/s), the proposed approach yields greater measurement accuracy (0.020 mm and 0.195 mm) than does the traditional spatial domain modulation (PS) method. In dynamic environments (15 mm/s), the proposed approach theoretically utilizes at least three patterns, with a defect rate lower than that of the nine-pattern, three-frequency PS method (8.58% and 14.68%).