Unlike document images, license plate images are mostly captured under uneven lighting conditions. In particular, a shadowed region has sharp intensity variation and sometimes that region has very high intensity by reflected light. This paper presents a new technique for thresholding license plate images. This approach consists of three parts. In the first part, it performs a rough thresholding and classifies the type of license plate to adjust some parameters optimally. Next, it identifies a shadow type and binarizes license plate images by adjusting the window size and location according to the shadow type. And finally, post-processing based on the cluster analysis is performed. Experimental results show that the proposed method outperformed five well-known methods.
© 2010 Optical Society of Korea
(070.4560) Fourier optics and signal processing : Data processing by optical means
(070.5010) Fourier optics and signal processing : Pattern recognition
(100.2000) Image processing : Digital image processing
(110.2960) Imaging systems : Image analysis
Original Manuscript: October 15, 2010
Revised Manuscript: December 7, 2010
Manuscript Accepted: December 8, 2010
Published: December 25, 2010
Min-Ki Kim, "Adaptive Thresholding Technique for Binarization of License Plate Images," J. Opt. Soc. Korea 14, 368-375 (2010)
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