Color Image Digital Watermarking Technology Research

With the rapid development of Information Techniques and the popularization of Internet, digital media(image, audio, video, etc.)has become the main means of information communication, people can easily acquire and spread a wide range of digital works through the Internet. Digital media is convenient to our life but accompanied with the more and more serious issue of the information security. The benefit of the author or the owner is harmed due to the illegal copied and tampered to the digital works, in the reason that this tamper is easily executed. So the protection of the copyright and the information security has become an urgent problem to be resolved. As a new information security technique, digital watermarking can provide efficient way for settling the problem of the copyright violation, illegal copying and dissemination, data disclosure and integrity. In recent years, the digital watermarking, especially for the color image arouse great attention and gain extensive research and application.In this thesis,the digital watermarking for the color image is researched. The research background and the present study of digital watermarking are given. The basic principle and the typical algorithm of digital image watermarking are mainly analyzed. The key techniques involving the digital watermarking for the color image, such as the concept of the color space, the principle and the property of DCT, and the application in digital watermarking, JPEG compression and process of the scrambling are investigated firstly. Then this thesis presented a dual digital watermarking algorithm for copyright protection and integrity authentication for color image based on DCT considering the disadvantage that only one watermark is embedded and the single function of most existing digital watermarking algorithms.The dual watermarking algorithm for color image based on the YCbCr color space, each component of the original color image is divided into non-overlapping 8×8 block, DCT and quantization is performed to each block, then a robust watermark for copyright protection and a semi-fragile watermark for tamper detection and location are embedded. To improve the robustness of watermark, this thesis adopted the multi-embedded strategy. The DC coefficients in the block of the same location of each color components, are embedded the same robust watermark. The robust watermark is a binary copyright image being transformed by Arnold. The intermediate coefficients in every block of luminance components, are embedded the semi-fragile watermark. The semi-fragile watermark is generated by the basic characteristics of original image. When extracting the watermark, value corresponding to the block is determined based on'majority principle'.In the experimental phase, image with watermark has been attacked in several ways, such as cropping, scaling, noise, JPEG compression and tampering. The results show that, the proposed dual watermarking algorithm, with an excellent transparent quality, is robust to normal image process and attack, and effective to identify the copyright of image. Moreover, the semi-fragile watermark can detect the tamper and locate the tampered regions accurately.