Study On The Anti-counterfeit Technique Based On The Screening Modulated By Pseudo Random Signal

The traditional anti-counterfeit-printing technique usually takes special ink, laser holographic image and line texture, but these are high cost and complexity technique. Compared to other anti-counterfeit-printing techniques, the halftone screening technique can decrease the cost of production and has good capability of anti-counterfeiting. So the research on the halftone screening is of great significance for its wide application.This paper advances the anti-counterfeit-printing technique based on the screening dot shapes modulated by pseudo random signal. While the original continuous tone image is converted to halftone image, the anti-counterfeiting information (such as graphic, image and text) is produced by encryption and error-correcting coding to generate pseudo-random signal. Then, using the look-up table method, the pseudo-random signal modulates the shapes of AM dots to be carried anti-counterfeiting information, so this can implement security features.After introducing the basic principles of halftone screening, human visual characteristics, image processing and display, this paper researches on AM and FM screening, explains their dot parameters, discusses template method, threshold method, growth model method and jitter method algorithm, summarizes the advantages and disadvantages of the two screening methods. The research focuses on the preprocessing algorithm, including pre-scrambling encryption, two-dimension interleaving coding and convolution coding, which improves the security and error-correcting performance of information. At the same time, this algorithm that generates pseudo-random signal is applied to AM screening halftone image. Using the look-up table method, the pseudo-random signal modulates the shapes of halftone dots to realize anti-counterfeit information embedded. Experimental results show that the proposed method can achieve anti-counterfeit features.