Automatic projector defocus measurement method with large depth of field for fringe projection system

Abstract The optimal defocus method is proved to be helpful to improve the accuracy of fringe projection measurement system. Using this characteristic, this paper proposes an automatic projector defocus method by using a self-designed control module to adjust the projector lens precisely. By applying automatic defocus to large depth of field measurements, the optimal defocus level at any position within the measurement range is determined. First, the gray histogram wave peak detection method is used to divide the object’s point cloud into multiple parts, and the optimal defocus measurement is performed to obtain multiple groups of point clouds. Then the linear interpolation method is used to solve the error of each point in the point cloud. Finally, the corresponding points are fused to get a set of point clouds with higher precision. The feasibility and effectiveness of the method are validated by experiments, which demonstrate an improved measurement accuracy of about 16% to the traditional method without defocusing.