低解析車牌影像之辨識

Abstract

近年來，雖然有許多關於車牌影像辨識的相關研究，但是卻鮮少有研究使用低解析的車牌影像作為輸入來進行辨識。因此，本論文將著墨在使用低解析度的車牌影像來進行辨識。這個方法可以處理極小的車牌影像，而且僅需單張車牌影像就可以進行處理。首先，針對單張影像，以人工方式將車牌區域截取出來作為為輸入，並進行連字符號的偵測以及定位車牌字母。其次，根據上個步驟所得之結果，使用單一字母進行樣版比對(template matching)，並挑選出適合的候選字母。最後，將單一字母樣版擴充至多重字母樣版來進行比對，逐步篩選並簡化辨識的結果。實驗結果顯示該方法對於低解析度的車牌影像具有相當的辨識率，且其結果也可有效應用在進行犯罪調查時，用以縮減嫌疑車輛的搜尋範圍。

Although there are lots of studies about recognizing vehicle license plate (VLP) images in recent years, the recognitions of low resolution VLP image are still deficient. The proposed method focuses on the recognitions of low-resolution VLP image. This method can treat VLP images with pretty small size, and only a single VLP image is need. First, the hyphen detection and character position estimation will be applied on a manually cropped VLP image which is seriously blurred. Then, a single-character template matching will be performed based on the estimated positions. Finally, the refinement of recognition results from the single-character template matching will be conducted via expanding a single-character template to a multiple-character template. Experiment results show that the proposed method is quite efficient to recognize VLP images with low resolution. The results are helpful for locating a suspect vehicle on a low-resolution image in the field of crime investigation.