Local enhancement of car image for license plate detection

Abstract

In this paper we address the problem of car plate detection. In the first part of algorithm we propose a method for enhancing car plate regions. We estimate the local density of vertical edges in the image as a criterion for local enhancement. In the second part, the vertical edges from the enhanced image is then extracted and feed to a morphological filter to constitute candidate regions for the place of car plate. This filter aims to connect vertical edges closer than the size of a defined structuring element. The output of this process is a number of connected components among which the plate region is. We use some geometrical features of car plate such as shape and aspect ratio to filter out non-plate regions from the candidate list. Using the correlation between the candidate regions and the model of car plate, the most probable region is found. The result of enhancement on car images shows the ability of the proposed method for improving the contrast of plate region(s) in the image. The experimental results on out-door car images confirms the robustness of the proposed method against the severe imaging condition.