Multiple Vehicle License Plates Localization and Extraction of Vehicle License Plate Number for Moving Vehicles

Nowadays, vehicle license plate (VLP) recognition system has become a key to lots of traffic related applications, e. g. the road traffic monitoring, the traffic analysis, the parking lots access control etc. Both accurately detecting the VLP from a vehicle image and extracting the VLP number from the detected VLPs are considered to be the most important stage of vehicle license plate recognition (VLPR) system. They greatly influence the overall recognition accuracy and processing speed of the whole system. This paper presents an algorithm to locate the multiple VLPs of moving vehicles from a video traffic image sequence, and adopts the projection scheme to extract the VLP number from the detected VLPs. The shifting of the VLP in the detected image is also studied and then a transformation based on relative position vector to correct the distorted plate image into a calibration standard image is developed. By means of the distortion calibration techniques, the VLP number in a distorted state can also be extracted more correctly. The experiment results show that the presented algorithm can correctly localize the VLPs even in overlapped vehicles situation and can effectively extract the VLP number from a distorted VLP caused by the shifting of relative position between the vehicle and the camera.