Car license plate detection based on MSER

Car license plate detection is a basic task in ITS. A MSER license plate detection method is proposed in the paper constrained by some priori knowledges of license plate. First the input image is pre-processed with grayscaling and gray stretching, etc, and then, the candidate MSER(Maximally Stable Extremal Region) license plate regions are chosen according to the pixel sum, the scale and length-width ratio of the license plate character region, next, the similar single-character regions are removed and the lower and upper borders of the license plate are determined in this step, using the constraints of the gray level jump and horizontal projection of candidate license plate character region, finally, the left and right borders of license plate are determined by vertical projection. The experimental results show the efficiency and robustness of the proposed method.