Robust recognition methods for inclined license plates under various illumination conditions outdoors

This paper presents novel methods of recognizing vehicle license plates robustly. To acquire fine images of quickly passing vehicles under a wide range of illumination conditions, we developed a sensing system having superb characteristics. We expanded the dynamic range and eliminated the blurring of images of fast moving vehicles by synthesizing a pair of images with different intensities. Furthermore, to extend the flexibility of the positioning of the TV camera, we propose a recognition algorithm which can be applied to much inclined plates. The performance of the integrated system was investigated on real images of highly inclined plates captured under various illumination conditions. The recognition rates of over 99% (conventional plates) and about 97% (highly inclined plates) show that the developed system is effective for license plate recognition.