An Application Of Digital Watermarking For Presswork Prevention

With the developing of the multimedia technique, and the inventing of the high performance printer and scanner, faking and pirating are rampant. And traditional technologies of the presswork forgery prevention have some shortcomings, such as high cost, complex technics, and small cover, result in the benefits of producers and customers are strictly losing. Compared to other forgery prevention techniques, the proposed techniques can decrease the cost of production and be completed easily. It is a significative try to introduce digital watermark technique in presswork forgery prevention field.Owing to the reasons putting out advanced, the paper gives algorithms for the text file and the color image. After researching current digital watermarking algorithms, studying print-and-scan processing, and analyzing the causes of distortion by printing and scanning, the main jobs are as follows:(1) For text files, no redundant information in them, a set of private character pattern is created to embed the secret information. And the difference between the private character pattern and system character pattern is hardly noticeable;(2) For color image, change RGB color space to CIE1976L*a*b* color space, which is irrelative to printer and scanner. And use scrambling algorithm setting up host image, transform the host image with the MALLAT-DWT to frequency domain. Then, embed the watermark into the mid-frequency and parts of low-frequency coefficients of 2nd and 3rd lays, where the texture is complex, with intelligent method. The algorithm is robust;(3) Considering the point of 6 trous-DWT is that the size of low-frequenpy band and high-frequency bands are as same as the size of the original image, and the quality of watermark picked out by fusion watermarking algorithm is high, an algorithm, based on the á trous-DWT and fusion watermarking, is proposed in the paper. Before embedded the spectrum of watermarking is spread. The security with the method is buildup, and the content is increased.At the aspect of extraction of (2) and (3), use the idea of multisensor data fusion theory for reference to make the extracted watermark clearer.In experiment, the printer is HP Color LaserJet 5550, and the scanner is EPSON Perfection 1200PHOTO. The efficiency of these algorithms have proved by the results of experiments.