Research And Application On Algorithm Digital Watermark Based On DWT

With the rapid development of digital communication and computer network technology, the spread and abtaining of digital information becomes more and more convenient. On one hand, rapid development of network has promoted the progress and development of society. On the one hand, it has brought a large number of new problems. As digital information can be copied, the copyright and security problems of multimedia products which published on the internet are more and more obvious. As people pay more attention to security and copyright problems of multimedia information, digital watermark technology which is a new method for protecting multimedia copyright in recent years has been widely studied and applied all over the world.Information hiding is an important technique of information security. Watermarking algorithm is a hot spot in the study of information hiding technology. In view of the great development and advantages of image processing of wavelet technology, digital watermarking algorithm based on DWT gradually becomes a popular study area of digital image watermark technology.The key issues of watermarking algorithm are encryption and insertion of watermark information. This paper presents a robust image watermarking algorithm in DWT domain that realizes the watermark insertion and extraction. Several common watermark attack measures, such as clipping, filtering, adding noise and compression are used to verify the robustness of the algorithm. Before inserting watermark information into the cover, firstly the Arnold mapping is used to scramble the watermark. Then the watermark information and Logistic generated chaotic sequence are combined by the XOR operation. The purpose of the above method is not only to overcome the insecurity brought by the cyclicity of Arnold, but also to prevent clipping. Base on the encrypted watermark, the DWT-based watermark embedding algorithm is introduced in this paper. The DWT-based watermark embedding algorithm uses encrypted binary image as watermark. Firstly, the cover is decomposed by second-order wavelet. And then, according to the characteristics of wavelet transform, the watermark is inserted into the second-order low frequency subband coefficients. And finally, the watermark invisibility and robustness is balanced by adjusting the watermark insertion factor.Algorithm introduced in this paper has been realized in programming. In this algorithm, the Normalized Correlation (NC) value of extracted watermark and the original one is approximately 1 when there is no attack. When the Stego cover is clipped to one-second of its original size, the NC value is up to 0.97. When Stego cover in JPEG is compressed to 50% of original size, the NC value is 0.86. The results show that the algorithm makes invisibility and robustness of the watermark well balanced.