Flexible calibration method for line-scan cameras using a stereo target with hollow stripes

With the advantages of ultrahigh resolution and acquisition rate, stereo line-scan sensors are gradually being developed for three-dimensional (3D) measurements. Calibration is crucial for line-scan cameras. However, viewing targets of line-scan cameras from different angles cause eccentricity errors. This paper presents a flexible calibration method for line-scan cameras to solve the eccentricity error problem. The calibration quality is improved by the accurate extraction of one-dimensional (1D) points on line-scan images, and the corresponding 3D points in space. Through the analysis of the eccentricity error in 1D image point extraction when utilizing targets with solid stripes, a stereo target with hollow stripes is designed. An algorithm is described to calculate the 3D points of intersection between the centerlines of hollow lines on the target and the viewing plane of the camera. A robust optimization is proposed to enhance the stability of parameter estimation. Experiments are performed to compare the re-projection error between the cross-ratio-based method and proposed method. A simulation is also performed to estimate the combined uncertainty. The comparative results of the experiments verify that the proposed method is accurate, low cost, and easy to implement.