1. Department of Criminal Science and Technology, Railway Police College, Zhengzhou 450053, China
2. Shanxi Provincial Key Laboratory of Microstructure Electromagnetic Functional Materials, Shanxi Datong University, Datong
037009, China
3. Institute of Public Safety Research，Zhengzhou University, Zhengzhou 450001，China
4. Wuxi Spectrum Vision Technology Co., Ltd., Wuxi 214000, China
5. Institute of Forensic Science, Ministry of Public Security, Beijing 100038, China
6. MOE Key Laboratory of Advanced Micro-Structured Materials, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Abstract：RMB is the legal currency of the people’s Republic of China. The authenticity of RMB is directly related to the harmony and stability of the society. As the most significant denomination bill in China, identifying the authenticity of 100 yuan RMB is more critical. In the paper, we use the visible/near-infrared hyperspectral imager to obtain the hyperspectral image data of an actual bill and two fake bills. Then select four feature points on the front and back of the bill to analyze the spectral differences between the front and back of the bill.From the spectral reflectance curves of the four characteristic positions on the front of the authentic and counterfeit banknote. It can be seen that the spectral reflectance of some patterns between the real and the counterfeit banknote varies greatly at different characteristic points, while that of some patterns is not significant. Moveover, for different batches of counterfeit banknotes, the spectral reflectance at different locations also has large differences. The analysis of the back of real and counterfeit banknotes shows that with different feature points, the spectral reflectivity between the real and the counterfeit banknote is also different in different bands. According to spectral reflectance curves of the 8 characteristic points on the front and back of the genuine and the counterfeit banknote, the grayscale images of the wavelengths at 500, 660 and 870 nm were selected. It was observed that the grayscale images of real and counterfeit banknotes showed obvious differences at different feature points.The image contour of the real banknote at 500 nm is clear. In 660 and 870 nm, no matter on the front or back, the real banknote has several characteristic positions different from the counterfeit banknotes. Therefore, it can be used to distinguish the real 100-yuan banknote at 660 or 870 nm. In order to highlight the difference between real banknotes and counterfeit banknotes, the gray-scale image of real and counterfeit banknotes of 100 yuan is obtained by band calculation. As can be seen from the figure, real banknotes are different from counterfeit banknotes in many places on the front and back sides. From the grayscale image of the first 12 principal components on the front of genuine and counterfeit banknote, it can be seen that there exist significant differences in each principal component no matter from the front or the back.According to the texture feature map on the front and back of the real and fake banknotes, it can be seen that the texture characteristics of the real banknotes are significantly different from the fake banknotes. The results show that the spectral reflectance of 100 yuan real banknotes is significantly different from that of different versions of counterfeit banknotes in the visible/near-infrared spectral range, and the differences between the front and back positions of 100 yuan real banknotes can be found by the near-infrared characteristic band, spectral operation, principal component analysis and texture characteristics. Therefore, visible/near-infrared hyperspectral imaging technology can be used to identify 100 yuan real and fake banknotes and provide the possibility and theoretical support for the traceability of counterfeit banknotes. The technology has practical significance in the actual practice of public security.
Key words：Hyperspectral imaging; Spectroscopic analysis; Principal component analysis; Identification of forged banknotes
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