Research On Preventing Secondary Printing Of Holographic Watermarking For Print Matter

As a new means of security, digital watermarking technology due to the advantage: difficult to imitation, easy to identify, low cost, and pollution-free, digital watermarking technology has become an important research content and the development direction for anti-counterfeiting in packaging and printing fields. The scanning equipment with precision and high assurance, resulting in a printed copy of counterfeit behavior is more common, were used so widely in package that seriously hampered China’s economic development, and make people’s normal life and social order stability extremely bad influences. Therefore, the effective,practical and efficient means of security to identify the product packaging has a very important practical meaning. In this paper, from the impact caused by the printing and scanned images paper, proposed a method of Fourier semi-fragile holographic watermark technology based on discrete wavelet transform to meet the need of watermark information: anti the first printing, prevent the second printing.Firstly, the paper analyzed the halftone technology of the translating digital image into printing image, and the color characteristics, texture,shape and spatial relationships characteristic features of the image were analyzed as well. The key reproduction technologies of printing image to the digital originals image was further studied. The digital image and the printed image features scanned by electron microscopy: the printed image can still be observed more clearly enlarged a certain multiple dot shape after, and the digital image enlarged the same time becomes blurred.Know the change rule of image after two times print-scanning, through the analysis of the image luminance component, than which provide the basis for watermarking algorithm is improved.For the image feature of pixel distortion caused by the geometric distortion, it proposed a Fourier semi-fragile CGH watermark based on discrete wavelet transform, and studied the influence of parameters on the watermark embedding image quality through simulation, combine to a zero-watermarking for double watermarking, the security provided forprinting double guarantee.Finally, by a series of print-scanning experiments, using normalized correlation coefficient(NC)as evaluation, the robustness and vulnerability of watermarking algorithm was analyzed. The first printing scanned image simulation, verification the robustness of the watermark. The results show that: the watermark information of different images can be presented and extract effectively after the first printing scan, It is showed that Watermarking algorithm meets the requirement of resistance to first print. After second print-scanning, the watermark information can’t be identified by human, which proves not only that the watermarking algorithm is robust, while there is a certain vulnerability, meeting the technical requirements of the anti-second printing.