An algorithm for the automatic analysis of characters located on car license plates

Abstract

The method for the analysis of signs visible on car license plates is described and experimentally evaluated in this paper. The algorithm is applied to the recognition of characters localised on car license plates, used in Poland. Emphasis is put on the especially complex cases - i.e. objects distorted by noise and occlusion - which are the most difficult and challenging tasks of the discussed problem and can be caused, for example, by bad weather conditions. The influence of poor quality images is another source of the problem. The modified UNL transform is applied to solve the problem. This is an algorithm for contour shape representation and recognition, which is not only invariant to affine transformations, but also robust against noise and occlusion. The algorithm is based on the transformation of points belonging to an object that has been extracted from the image from Cartesian to polar coordinates. © 2013 Springer-Verlag.