即時動態車牌辨識

Dynamic Real-Time License Plate Recognition

本文使用1394攝影機拍攝車牌影像，並與電腦連結，再由Matlab/Simulink偵測車牌存在與否。當偵測到車牌時，Matlab/Simulink 會自動儲存所偵測之車牌影像，再開啟所設計的GUI 辨識介面，以讀取所儲存的車牌影像，再執行車牌定位、車牌傾斜矯正、字元分割及字元辨識等步驟。首先，以連通標記法搭配車牌區域分析來偵測車牌位置，如所拍攝車牌傾斜時，再以雷登轉換來矯正車牌，進而以投影切割法分割車牌字元。於車牌辨識率部份，以改良式主成份分析法擷取字元特徵，再搭配歐式距離決策法，以探討搭配使用及未使用簡單分類器之車牌辨識的差異。由結果得知，搭配使用與未使用簡單分類器之字元辨識成功率分別為95.9%與87.4%左右，而其辨識時間分別為1.3 秒／張與0.8秒／張，所測試影像皆為640 × 480大小。而因字元「B」和「8」、「D」和「0」、「5」和「S」、「2」和「Z」及「1」和「I」的字型相當相似，為改善相似符號難以辨別的問題，吾人利用字元邊緣線特徵的差異，作為相似符號確認的依據。

This paper presents a dynamic real-time license plate recognitionmethod using a 1394-based digital camera to record an image of a licenseplate and process the image with Matlab/Simulink based on GUI (graphicaluser interface). If the program detects a license plate in the image, therecognition system will automaticlly store the image and execute licenseplate localization, license plate slant correction, character segmentation andcharacter recognition. First, the license plate in the image is localized byapplying connected component analysis with the aid of license plate areaanalysis. If the localized license plate is slanted, the plate slant iscorrected using Radon transform and its plate character is then segmentedby projection histogram. As for license plate recognition, an improved principal component analysis using the Euclidean distance method withand without the aid of using a simple classifier to extract the features of theplate characters and the classification of the plate is investigated in thispaper. As a result, the recognition rates of license plates for 640 × 480pixel images are approximately 95.9% and 87.4% with and without the aidof a simple classifier, respectively. Their corresponding recognition timesper license plate are about 1.3 and 0.8 seconds, respectively. Moreover,recognition of ambiguous characters on license plates such as the sets of“B” and “8”, “D” and “0”, “5” and “S”, “2” and “Z” as well as “1” and “I”are analyzed by using the difference between their edges to increase therecognition rate.