License plate detection using topology of characters and outer contour

Abstract

This paper presents a license plate detection method for detecting license plates on vehicles, using the topology of painted numbers and letters and the outer contour of the license plate. Even in the situation of poor illumination, the contrast is often high between the background and the characters on the license plate; this makes the detection of characters on the license plate possible, when the license plate is free from occlusion within the image. The characters are detected using the topological information from the character candidates, and then the license plate is detected by extracting the vertical and horizontal edges in proximity of the detected character's region. In the case of a failure to detect the license plate region by the edge detection method, an extended region encompassing the detected character is converted to a binary image, and then all the characters present on the license plate are detected. We verify the performance of this algorithm by experiments on a large dataset of images with varying complexity. © 2008 IEEE.