A novel iterative calibration approach for thermal infrared cameras

The accurate geometric calibration of thermal infrared (IR) cameras is of vital importance in many computer vision applications. In general, the calibration procedure consists of localizing a set of calibration points within a calibration image. This set is subsequently used to solve for the camera parameters. However, due to the physical limitations of the IR acquisition process, the localization of the calibration points often poses difficulties, subsequently leading to unsatisfying calibration results. In this work a novel IR camera calibration approach is introduced. It is able to localize the calibration points within the images of a conventional calibration board consisting of miniature light-bulbs with improved accuracy. Our algorithm models the radiation pattern of each light bulb as an ellipse and considers the center of mass of the extracted ellipsoidal region as the starting calibration point, which is refined iteratively using alternating mappings to and from an undistorted grid model. The proposed processing chain leads to a significantly reduced calibration error when compared to the state-of-the-art. Furthermore, the proposed methodology can also be used to calibrate visible-light cameras thus being suitable for the calibration of multiple camera rigs involving both visible-light and IR cameras.