Research on method of avoiding phase unwrapping error in 3D measurement of gray code

In the field of industrial automation, accurate acquisition of object three-dimensional information is beneficial to better product design. Structured light three-dimensional measurement technique has been widely used in industrial inspection and reverse engineering because of its advantages of non-contact and high measurement accuracy. The structured light three-dimensional measurement technique combined with gray code and phase shift method has high efficiency and strong robustness. However, in the process of extract the phase map of the measured objects, there will be misalignment between the wrapped phase and the fringe order. This will lead to the jump error of wrapping phase edge in phase unwrapping process, which will reduce the measurement accuracy. To solve this problem, the fast tripartite phase unwrapping method is proposed in this paper, which can effectively eliminate the phase unwrapping error and significantly improve the computational efficiency. Firstly, the mask image is obtained by threshold segmentation of full-bright images using OTSU method. Subsequently, phase unwrapping is carried out under the guidance of gray code coding sequence, and the absolute phase value of the target is obtained. In the process of phase unwrapping, the mask image is used as the guide to improve the phase decoding efficiency, and tripartite phase unwrapping method is used to eliminate the phase unwrapping error. Experimental results show that this algorithm eliminates the edge jump error and improves the efficiency of normal gray code phase unwrapping method.