Research On Color Image Digital Watermarking Technique

With the rapid development of network and computer, digital media including digital image has been widespread used. But the problems of information security of digital media occur. On one hand, digital image can be found on web everywhere, copying,editing and diffusing image become a very easy job in information era; On the other hand, digital image processing technology has been mature, it is possible to forge and tamper original image. Copyright protection and content authentication of image trouble people increasingly and need to solve those problems urgently. Traditional encryption method can protect data in a certain extent. But once the key is got by attacker, data will be lost without any control. Originator can't trace the copy of image and the action of diffuse. The security encryption was doubted by people. In this situation digital watermarking technology emerge. Digital watermarking is an effective method to the copyright protection and content authentication of digital media and has been a hot issue in information security domain.After studing the basic theory of digital watermarking technology and existed watermarking algorithm, study and analysis the color image digital watermarking carefully. The essay has four parts as follows: related study state of digital watermarking, including the application background and technology background, its status in home and abroad and its application domains; basic knowledge of digital watermarking: general system structure, the attacks to image digital watermarking, requirements of watermarking algorithm, and robustness and invisibility of watermarking algorithm etc. Studing existed related image watermarking algorithms including both spatial algorithm and transform algorithm. Two watermarking schema were presented. One is a DWT-SVD based color image watermarking algorithm. A gray image as watermark is embedded into blue component of color image by combining Human Visual System (HVS), and by comparing SNR perceptive quality of original image when watermark is embedded in blue component can obtain better than other color components. The experiment results show that the watermarking schema is very robust to JPEG compressing,median filtering and other attacks.Another is a color image watermarking schema which achieves copyright protection and content authentication simultaneously. Fragile watermark was embedded into the blue components of color image for image authentication and robust watermark was embedded into the green components of color image for copyright protection. Comparing existed schema, The experiments show that the algorithm can assure good imperceptibility for watermarked image, the watermark embedded for Copyright Protection is robustness to JPEG compress,Gaussian noise and so on by computing the same bit percent, and the watermark embedded for content authentication cannot only characterize attract but also localize the modifications made to the image effectively; the embedding position of watermark for copyright protection is selected randomly, watermark for content authentication was scrambled before embedding, so security of schema is enhanced.