Flexible Projector Calibration in the Structured Light 3D Measurement System

In the structured light 3D shape measurement system, the projector plays an essential part for 3D shape reconstruction. As the projector calibration accuracy affects the 3D shape measurement accuracy, a flexible projector calibration approach in the structured light system is proposed. Key to the proposed method is to establish the relationship between the projector coordinate and the world coordinate using the pre-calibrated camera. The process of the system calibration can be divided into three steps. First, a black-and-white (B/W) checkerboard is pasted on the white board plane for camera calibration. Second, the pre-calibrated camera is used to obtain the 3D world coordinates of the checkerboard corners. Here, instead of using complicated process with spatial color illuminations or phase-unwrapping method for the pixel mapping, a projected B/W checkerboard is used for the projector calibration. Unlike some other methods, the non-wide-angle camera can be used to capture the images of both pasted and projected checkerboards. Also the calibration process is not vulnerable to the environment. Finally, the results of the camera and projector calibration are used to reconstruct 3D shape. Experiments show that the reprojection errors for both camera and projector are within ±1 pixel, and the RMS error of 3D reconstruction is 0.25 mm.