HSI color based vehicle license plate detection

Vehicle license plate recognition (VLPR) is one of the most important topics of using computer vision and pattern recognition in intelligent transportation systems. In order to recognize a license plate (LP) expeditiously, the location of the LP in most cases, must be detected in the initial step. For this reason, detecting the exact and perfect location of a LP from a vehicle image is considered to be the most important and crucial step of a VLPR system, which greatly affects the recognition process and directly influences the accuracy and speed of entire system. In this paper a HSI color based license plate detection method is proposed. In this method, (a) HSI color model is used for detecting candidate regions and (b) vehicle license plate (VLP) regions are verified and detected by using position histogram. In the proposed method, input vehicle images are converted into HSI color images. Then the candidate regions are found by HSI color model on the basis of using hue, saturation and/or intensity. These candidate regions may include LP regions; geometrical properties of LP are then used for classification. Finally, VLP regions containing predetermined LP alphanumeric character are verified and detected by using position histogram. The proposed method is very effective in coping with different conditions such as poor illumination and varied weather comparing with traditional approaches. Experimental results show that the distance from the vehicle varied according to the camera setup.