Transform Domain-based Digital Watermark Technology

With the evolution and booming of network and multimedia technology, Internet becomes one of the most important way for information spreading. But illegal copies and pirate comes together with it. There have emerged many techniques for protecting the security of multimedia information in digital world in recent year. Image digital watermark technique is a new copyright protection technique , which, in fact, is information hiding technique used in image processing field. The fundamental of this approach is embedding digital watermark information into image, at the same time keeping the image quality degradation imperceptual . This is an effective way for copyright protection.This paper is focused on image watermarking algorithms. Watermark casting operates in frequency domain, embeds pseudo-random sequence of real number in selected coefficients without image degradation. A blind watermark retrieval technique that can detect the embedded watermark without resorting the original mage is proposed, so that the proposed techniques represent a major improvement to those relying on the comparison between the watermarked and original image,which is not practical for a huge image database. All process, include watermark embeding, extracting and verification are simulated in MATLAB environments.This paper include six chapers. In chapter 1, we introduced the source of digital watermarking and its relation between information hiding, the method, target and meaning of this dissertation were presented. In chapter 2, we discussed the classic algorithm system, the structure model, and its special characters in this chapter too; In chapter 3, we introduced the human visiual system and the process ofdigital image and the choice of Matlab. In chapter 4,we introduce a system based on DCT domain, include the definition of DCT and the process of the digital watermark system based on DCT.In chapter 5,we introduce a syetem based on DWT domain.inculed the definition of DWT and the process of the digital watermari system based on DWT. In DCT based system,select DC and mid-frequency as the watermark carrier for the consideration of the trade off between the imperceptibility and robustness requirements. In DWT base system, a couple of siginificant wavelet coefficients in detailed subbands are selected to embed watermarks by first level decomposing. A better image quality (imperceptibility) can be gained by exploiting human visual system.