Line-based nonlinear distortion correction of a calibration image

In view of a calibration image in a tube camber measurement system, a nonlinear distortion correction method utilizing linear characteristic is presented. Straight lines in the three dimensional world must project to straight lines in the image plane, if the distortion is compensated effectively. The first step of the method consists of extracting edges from the image by using an edge detection method. And many outliers can be eliminated based on the length of edge segments. The sum of the distortion error of each edge candidate is the objective function. The optimal distortion coefficients can be obtained by minimizing the objective function. Thus the nonlinear distortion of the calibration image can be corrected. Experimental results show that the corrected image meets the need of precision of the tube camber measurement system. And the method can easily be applied.