An improved method for Vietnam License Plate location

Abstract

The License Plate Location (LPL) from the vehicle images is the key step in the Automatic License Plate Recognition (ALPR). In this paper we proposed a new LPL algorithm for Vietnam license plates, which combined preprocessing, morphology operation on grayscale image, image subtract operation on grayscale image, image binarization based on threshold, edge detection use Canny operator, morphology operation on binary image, finding the license plate (LP) angle & rotating LP based Radon transform and bilinear interpolation, and then cutting exactly license plate region based on measuring properties of Vietnam license plate regions. Specially, by the combined morphology operation & subtract operation on the grayscale image, which very efficiency for complex background images, night & day images and different illumination, different light conditions, we have obtained the better image with new intensity values, which more satisfied for the image binarization and reduced candidate regions. And we used opening operation on binary image to remove small objects (noise areas), and by the measuring properties of license plate regions we had cut exactly for different Vietnam license plate dimensions (one-row and two row LP). So, the proposed approach is more effective than some of the existing method earlier and very satisfied with Vietnam license plates. Experiments have been implemented on 500 images taken from different background: lightening conditions (night and day), license angles, illumination, size and type of license plates, colors, reflected light, dynamic conditions. The efficiency of processing of the proposed algorithm is improved and average rate of accuracy of the LPL is 97.27%, and proposed method is suitable for all of color license plates.