Character Segmentation Method for a License Plate with Topological Transform

Authors: Jaedo Kim, Youngjoon Han, Hernsoo Hahn

Abstract:

This paper propose the robust character segmentation method for license plate with topological transform such as twist,rotation. The first step of the proposed method is to find a candidate region for character and license plate. The character or license plate must be appeared as closed loop in the edge image. In the case of detecting candidate for character region, the evaluation of detected region is using topological relationship between each character. When this method decides license plate candidate region, character features in the region with binarization are used. After binarization for the detected candidate region, each character region is decided again. In this step, each character region is fitted more than previous step. In the next step, the method checks other character regions with different scale near the detected character regions, because most license plates have license numbers with some meaningful characters around them. The method uses perspective projection for geometrical normalization. If there is topological distortion in the character region, the method projects the region on a template which is defined as standard license plate using perspective projection. In this step, the method is able to separate each number region and small meaningful characters. The evaluation results are tested with a number of test images.

Keywords: License Plate Detection, Character Segmentation, Perspective Projection, Topological Transform.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1055741

References:

[1] H. Bai, J. Zhu, C. Liu, "A fast license plate extraction method on complex background," Intelligent Transportation Systems, Proceedings. 2003 IEEE, vol. 2, pp. 985-987.
[2] D. Zheng, Y. Zhao, and J. Wang, "An efficient method of license plate location," Pattern Recognit. Lett., vol. 26, no. 15, pp.2431-2438, Nov. 2005.
[3] Jung-Wei Hsieh, Shin-Hao Yu, and Yung-Sheng Chen, "Morphology-based license plate detection in images of differently illuminated and oriented cars," Journal of Electronic Imaging, Vol.11, No. 4, pp. 507-516, 2002.
[4] X. Shi, W. Zhao, and Y. Shen, Automatic License Plate Recognition System Based on Color Image Processing, vol. 3483, O. Gervasi et al., Ed. New York: Springer-Verlag, 2005, pp. 1159-1168.
[5] G. Cao, J. Chen, and J. Jiang, "An adaptive approach to vehicle license plate localization", in Proc. 29th Annu. Conf. IECON, 2003, pp. 1786-1791.
[6] Feng Wang, Lichun Man, Bangping Wang, Yijun Xiao, Wei Pan, Xiaochun Lu, "Fuzzy-based algorithm for color recognition of license plates," Pattern Recognition Letters, Vol. 29 , No. 7, pp. 1007-1020, May. 2008.
[7] Wu Guo-ping, Cheng Shi, Ao Min-si, Lei Hui, "Slant Correction of Vehicle License Plate Based on Feature Point and Principal Component Analysis," International Conference on Computer Science and Software Engineering, vol. 6, pp.487-490, 2008.
[8] Hsien-Chu WU, Chwei-Shyong TSAI, and Ching-Hao LAI, "A license plate recognition system in E-Government," An International Journal Information & Security, Vol. 15, No. 2, 2004, pp. 199-210.