Printing Watermark Applied Basic Research

With the development of image's high-fidelity in-out equipments, especially high-fidelity color spray-ink, laser printers and high-fidelity color duplicating machines, the forgery of presswork like money, check and merchandise packaging is easier then before. We used to protect the presswork with forgery-preventing technology. However these technologies have a lot of disadvantages. We need a new technology to solve these problems, therefore presswork watermarking is proposed.Because the key of presswork watermark is resist PS (printing and scanning) attack, we propose a new watermark algorithm which has good robustness and is able to resist PS attack. Considering robustness of watermark, we choice low frequency Coefficients of DWT(Discrete Wavelet Transformation) to embed black and white watermark. Moreover, we consider the characters of HVS (Human Visual System), consequently watermark has nice invisibility. The self-adaptive choice of watermark strength is based on two aspects. The one is brightness and contrast mask, the other is texture mask. We consider these two aspects synthetically. And this is a innovation of mine. We use new chaos permutation method to permute the watermark image. The method that base on mixed-optical bistable chaotic sequence has nice permutation effect and high security. The key of permutation is initial value of chaos sequence; Basing on the researching of image's printing and scanning process, we propose a new approach to correct brightness errors of image that have subjected to PS attack. This approach that use a so-called brightness error matrix make watermark can resist PS attack. Most importantly, the results of experiments prove that method can resist ordinary attack(JPEG compressing,shearing,dirtying,adding noise,filtering) and PS attack. The watermark extract from images is clear, thus we can use it to proof the copyright of presswork. The embedding of watermark is not affect the visibility of images. The new algorithm is the base of application for presswork watermark.