The Research Of Spread Spectrum And Phase Modulation Techniques Applied In The Digital Watermark

Digital watermarking is an effective way for copyright protection in the internet age, it can identify whether the media is protected or not, tail the protected data spreading, distinguish facts and figments, control the illegal copies, solve dissensions of copyright and provide proofs for the court, and it has become a hot research topic in the multimedia security field.The processing of digital watermark is very similar to a communication course, by combining the spread spectrum technique and the phase modulation technique with the watermark algorithm skillfully, two creative algorithms based on DCT and DFT separately were proposed in this paper. Some good results were obtained such as large quantities of information embedding, imperceptibility of watermark and the ability of resisting various attacks on watermarked image.Digital watermarking algorithm based on DCT was proposed by applying the spread spectrum technique. The imperceptibility of watermark was guaranteed by selecting the textured image blocks appropriately;the application of spread spectrum technique enhances the embedding capability of information and the ability of resisting attacks. Simulated experiments show the proposed algorithm is very robust to several image manipulations such as JPEG compression, noising, filtering and image cropping.Digital watermarking algorithm based on DFT was proposed by applying the phase modulation technique, the algorithm adopted two strategies — low amplitude block selection and amplitude boost to enhance its performances. The algorithm not only realized embedding watermark invisibility, but also enhanced the robustness of the watermark;embedding with large quantities of information was realized by selecting the phase difference which came from the neighboring blocks. Simulations show the algorithm is robust to attacks such as JPEG compression, noising, filtering, painting and 1/4 image cropping, the extracted watermark with high normal correlation value was obtained by twice embedding.