Pixelwise calibration and measurement method of dense laser stripes with large diffraction and distortion

Laser three-dimensional (3D) scanner is widely used to obtain the 3D shapes in complex scenes. The more stripes of laser 3D scanner, the higher measurement efficiency. However, dense laser stripes (DLS) (more than 20 laser stripes) causes large angle diffraction and increases the manufacturing distortion, which significantly decreased the accuracy of the DLS 3D scanner. To address this issue, we propose a pixelwise calibration and measurement method for DLS 3D scanner. In calibration, the DLS are projected onto a calibration tool. Two cameras capture the deformed DLS patterns. We use the stereo rectification and center extraction to obtain the center points of each stripe in two patterns. Then, we move the calibration tool to different distances, and obtain the center points of each stripe in different distances. We select the center points at different distances for each row of each stripe, and model the relationship between two cameras by a cubic equation in one variable in the imaging plane with these center points. We repeat the process for all the rows of stripes, so as to create the pixelwise relation between the two cameras and DLS. The experimental results show that the mean calibration accuracy of the proposed method is 96% higher than that of the planar model and 92% higher than that of the 3D quadratic surface model. In measurement, we take advantage of the calibrated DLS system to increase the measurement precision. The center points are corrected with the calibrated parameters row by row, stripe by stripe using least squares iterations. The experimental results show that the measurement accuracy of the standard spheres increased by 40% and that of low-reflectivity objects increased by 74% compared to the results of stereo reconstruction.