Procedures of correction of the geometry distortions for digital images

The existing techniques for camera calibration can be classified into the following categories: Direct Nonlinear Minimization, Closed-Form Solution, Two-Step Method. As rule of thumb, iterative methods involve closed-form solution of linear equations without the estimate of distortion parameters, while noniterative methods allow to evaluate lens distortion through nonlinear optimization procedures, but require a good initial guess of the parameters. In this paper we present an alternative two-step method based on combination of Tsai-Lenz and Cohen-Herniou camera calibration techniques. Advantages of this approach can be summarized as follows: the algorithm in the first step is noniterative, therefore fast, and easy to implement; compared to Tsai method, our second step improve the computation of all parameters; the nonlinear optimization step can take into account different types of lens distortions.