High-speed 3D shape measurement using the optimized composite fringe patterns and stereo-assisted structured light system

TLDR

Typical fringe periods (~20) constrain phase‑unwrapping stability and thus limit 3D measurement accuracy. The authors aim to design an optimized composite fringe pattern that embeds speckle into conventional 4‑step phase‑shifting patterns and to propose a correlation‑quality criterion, thereby improving phase‑measurement accuracy and speed. By combining stereo‑assisted structured light, stereo phase unwrapping, adaptive‑window image correlation, and regional diffusion compensation, the method recovers an accurate, unambiguous, distortion‑free 3D point cloud using only four projected patterns. Experiments show the technique delivers high‑speed (5000 fps), high‑accuracy, robust 3D shape measurement with dense 64‑period fringe patterns.

Abstract

In this paper, we propose a high-speed 3D shape measurement technique based on the optimized composite fringe patterns and stereo-assisted structured light system. Stereo phase unwrapping, as a new-fashioned method for absolute phase retrieval based on the multi-view geometric constraints, can eliminate the phase ambiguities and obtain a continuous phase map without projecting any additional patterns. However, in order to ensure the stability of phase unwrapping, the period of fringe is generally around 20, which limits the accuracy of 3D measurement. To solve this problem, we develop an optimized method for designing the composite pattern, in which the speckle pattern is embedded into the conventional 4-step phase-shifting fringe patterns without compromising the fringe modulation, and thus the phase measurement accuracy. We also present a simple and effective evaluation criterion for the correlation quality of the designed speckle pattern in order to improve the matching accuracy significantly. When the embedded speckle pattern is demodulated, the periodic ambiguities in the wrapped phase can be eliminated by combining the adaptive window image correlation with geometry constraint. Finally, some mismatched regions are further corrected based on the proposed regional diffusion compensation technique (RDC). These proposed techniques constitute a complete computational framework that allows to effectively recover an accurate, unambiguous, and distortion-free 3D point cloud with only 4 projected patterns. Experimental results verify that our method can achieve high-speed, high-accuracy, robust 3D shape measurement with dense (64-period) fringe patterns at 5000 frames per second.