Fish-eye cameras are widely used on many occasions due to their ultrawide field of view (about 180°). In this paper, we present a high-precision two-step calibration method to calibrate fish-eye cameras. The two steps are the global polynomial projection model fitting and local line-fitting calibration optimization. In the first step, we obtain the projection model of the fish-eye camera and apply a quartic polynomial to fit the projection model over the entire image. In the second step, the fish-eye image is partitioned into several sections and line fitting is adopted in each section in order to further reduce the residual error of the first calibration step. Experiments show that the new method is able to correct the distortion of the real scene image well. In addition, its average reprojection error is 0.15 pixel better than 0.40 pixel of the general projection model described. The reason that higher calibration precision is obtained is that this method not only considers the global projection model of the fish-eye camera but also considers the local characteristics, such as small tangential distortion and asymmetry.
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