关键词: 车牌字符提取, 压缩域, 运动图像专家组标准（之一）（MPEG-2）

Abstract: To extract the characters in vehicle plate, which is a special scene image, a compressed-domain text extraction algorithm is proposed. It integrates text region detection, location, tracking and text recognition in a united framework. Since DCT coefficients can be directly utilized to represent the texture feature, a decision rule for adaptive threshold is defined based on the sum of weighted frequency components to detect the plate region. The text region is further located by the projection profile of DC+2AC texture intensity. The inter-frame text region tracking is completed by using the average motion vector of some macro-blocks, whose intersected area with located vehicle plate is larger than predefined value. The OTSU algorithm is adopted to convert the decompressed vehicle plate into binary image for OCR processing. Experiment demonstrates the effectiveness of the proposed approach. The recall and precision ratios can reach up to 95% and 96.2%, respectively. It is suitable for the text extraction of other type’s scene as well.

Key words: vehicle plate character extraction, compressed domain, Moving Picture Experts Group（MPEG）-2