Optimized calibration method for ultra-field dual bands cameras based on thermal radiation checkerboard.

• An automatic calibration method is proposed for the ultra-field infrared and visible cameras. • A thermal radiation checkerboard is designed, which can be used in infrared and visible bands at the same time. • The corners and center can be automatically located at subpixel level. • RBF based nonlinear refinement is proposed to improve the calibration accuracy. Camera calibration is a vital and important work for machine vision. In the paper, an optimized calibration method for ultra-field dual bands cameras is proposed, which is based on the designed thermal radiation checkerboard. The optimizations are achieved in subpixel location, center location and mapping relationship, respectively. Specifically, the subpixel corner is located by performing the designed variable quadrilateral template on edge gradients and calculating their minimum orthogonal value. Then, the center location is accomplished through Gaussian fitting, in which the bottom point is taken as the potential center in iterations. Moreover, the RBF network is employed to replace the polynomial fitting and fit the mapping relationship between the camera coordinates and sensor coordinates. Thus, the accuracy of the mapping is increased, which contributes to the optimization of the intrinsic and extrinsic parameters. The experiments results show that the average root mean square error of the reprojection is reduced by nearly 50%. The calibrated parameters are accurate and have physical significance in the proposed calibration scheme. [ABSTRACT FROM AUTHOR]