Ofdm-based Robust Digital Watermarking Technology Research

With the rapid development of internet and information technology,the internet is becoming a mainly transform method,more and more productions are spreading through internet,it provides advantages,but also some difficulties,how to protect the legal interest of the possessor,and how to benefit more people are questions we need to consider.The digital watermarking technique emerged as the times require,it is widely used in copyright protecting and text authentication,and attracted much attentions.Compared the robust watermarking system with the communication system,we defined the communication model of robust watermarking system.Derived a conclusion that all technologies which can resist interference can also be used to promote the robustness of the watermark.Through experimental simulation,we studied the influence that JPEG compression and geometric crop brings to the coefficients(DCT domain,DWT domain,mix domain) of the image,and relevant embedding policies are proposed.A novel robust watermarking algorithm based on OFDM is proposed.The original watermark is randomized,and then encoded with OFDM technology and orthogonal transform,then the watermarking sequence(?) is formed;the PAPR of the signal is reduced through orthogonal transform,and the robustness of the watermark is enhanced,the extraction of watermarking can be accomplished blindly.The carder image is decomposed into 2 classes by DWT,and the DCT is applied to the approximate band LL2,and then the watermark information(?) is embedded to these coefficients I' which have minimum variance.The damage of the image is diminished through this embedding policy,and the robustness of the watermarking is improved.The MATLAB simulation shows that,①the performance of resisting geometric attacks of the watermarking is improved by OFDM technology,②the performance of resisting JPEG compression is very well,the watermarking can be detected without distortion when the QF＞=15,③the NC of the watermark is above 0.92 when the crop ratio is 1/3,④the detected watermark is very clear when the image is shifted,resized and rotated,and the watermark is robust to med-value filtering,wiener filtering,Gaussian noise and so on.⑤the performance of resisting geometric attacks by 4*4 divided-blocks is better than 8*8 divided-blocks of DCT transform,⑥The capability of this scheme is large,and the watermark can be extracted blindly.