A STUDY ON A GENERIC CHARACTER EXTRACTION METHOD FOR VEHICLE LICENSE PLATES USING PROJECTIVE TRANSFORMATION

Abstract

 In Japan, AI is being incorporated into automobile traffic volume surveys to enhance efficiency. By recognizing license plates in these surveys, it's possible to measure vehicle flow, refining the accuracy of the survey. However, when the video footage is taken from a high vantage point on the road's shoulder, the license plates appear tilted. To correct this, the image needs to be adjusted to a frontal orientation. If the license plate and the vehicle have the same color, determining a reference point for the projective transformation becomes challenging. To address this issue, we developed a method that corrects the license plate to a front-facing orientation using a projective transformation, based on the position of the fourth digit of the serial number—a consistent feature on all license plates. Our experimental results indicated successful character extraction from 479 out of 500 images. We aim to apply this technique in future traffic flow studies to identify the same vehicle at multiple locations.