Introducing free-function camera calibration model for central-projection and omni-directional lenses

To ensure making valid decisions with high accuracy in machine vision systems such as driver-assistant systems, a primary key factor is to have accurate measurements, which means that we need accurate camera calibration for various optical designs and a very fast approach to analyse the calibration data in real-time. Conventional methods have specific limitations such as limited accuracy, instability by using complex models, difficulties to model the local lens distortions and limitation in real-time calculations that altogether show the necessity to introduce new solutions. We introduce a new model for lens distortion modelling with high accuracies beyond conventional models while yet allowing real-time calculation. The concept is based on Free-Function modelling in a posterior calibration step using the initial distortion estimation and the corresponding residuals on the observations as input information. Free-Function model is the technique of numerically and locally modelling the lens distortion field by assuming unknown functions in our calibration model. This increases the model’s flexibility to fit to different optical designs and be able to model the very local lens distortions. Using the Free-Function model one can observe great enhancements in accuracy (in comparison with classical models). Furthermore, by increasing the number of control points and improving their distribution the quality of lens modelling would be improved; a characteristic which is not present in the classical methods.