Pixel-wise calibration method based on the virtual plane for telecentric structured light system

Micro three-dimensional (3D) imaging technology based on structured light is widely used in industrial applications, as it can obtain high -precision morphology of tiny objects using a camera equipped with a telecentric lens and a distorted pinhole projector. However, the telecentric structured light system suffers from problems caused by stereo -vision degeneracy, and their measurement accuracy is limited due to local distortions in stereovision calibration. To overcome these issues, the paper proposed a pixel -wise calibration method based on the virtual plane. In this method, first, the virtual plane is applied to the telecentric structured light system to ensure spatial relationships between the camera and projector, which is achieved easily by the Levenberg-Marquardtbased Perspective-n-Point(PnP) algorithm. Second, a pixel -wise polynomial regression model is introduced for local distortions, which converts phase information into refined 3D coordinates. Third, considering orthogonal stripes have poor sensitivity in one direction, the optimal fringe selection based on a reference plane is used in the calibration process to make the system more sensitive to depth. In addition, the proposed method can be extended to multi -projector systems and allows uncalibrated projectors to be calibrated with unidirectional fringe patterns. The proposed calibration method is flexible and easy to conduct. Experimental results demonstrate that our proposed method can effectively reduce local measurement errors and significantly improve reconstruction speed.