关键词: 交通工程, 多车牌定位, 小波变换, 图像增强, 灰度跳变, 行定位

Abstract: Aiming at the problem of extracting multiple license plates from complex background, an improved two-dimensional discrete wavelet transform was proposed to locate multiple license plates. Firstly, according to the characteristics of wavelet multi-scale decomposition, the two-dimensional discrete wavelet transform was applied to the image to obtain a series of low-frequency wavelet information maps. A linear difference with the original image was made to obtain the detailed features of the license plate characters. Secondly, according to the difference between the characters of license plate and the background in the binary image, the gray level jump was generated, the line position of license plate in the image was roughly located, and the search range of license plate location was narrowed. Finally all license plates were accurately located by using color and shape features, in the small range image of rough location. The research results show that compared with the traditional two-dimensional discrete wavelet transform image, the improved two-dimensional discrete wavelet transform image has nearly doubled the gray level mean value, standard deviation and average gradient, which can effectively obtain the edge information of the original image to narrow the position of multiple license plates. The multi-license plate location method can achieve an accurate positioning rate of 98.96%, with an average time of 328 milliseconds. It can be seen that the proposed method can accurately and quickly locate multiple license plates.

Key words: traffic engineering, multi-license plate location, wavelet transform, image enhancement, gray level jump, line position