Piecewise distortion correction for fisheye lenses
Lens distortion is a well-known problem for camera calibration. In particular in applications where a large amount of low-quality acquisition devices is adopted, like, e.g. embedded systems or Cyber-Physical Systems (CPS), a complete re-sectioning and undistortion in different operating conditions (e.g. autofocus, zooming) could not be feasible and accurate. Usually undistortion is obtained building a proper invertible geometrical distortion model with a specific number of parameters, but, unfortunately with the actually available low cost wide-angle and ultra wide-angle lenses a simple mathematical model for a global closed form solution can be ineffective in practical cases in particular in the peripheral image regions. In order to account for these problems we present a novel local correction approach based on the planarity and orthogonality constrains for a planar target (a checkerboard) where a Look-Up Table (LUT) is built to provide the minimum displacement for every pixel in the target region minimizing interpolation and residual distortion. The proposed method can also be considered a preliminary step in order to recognize image elements before global undistortion e.g. for features matching in images stitching.