Digital Watermark Based On Wavelet Domain Algorithm

With the development of computer and network technology especially the rapid growth of Internet users and the startup of electronic business, it is a tendency to publish and convey digital products on networks. However, digital products are liable to be infringed and duplicated in the procedure of publishing and conveying. Although networks provide many conveniences for human, they render us a new research subject: content reliability protection and copyright protection. Digital watermark is an important technology to this subject. Watermarking utilizes a digital method to embed some markers which have special meanings into digital images, audio, documents and video. Watermark can testify the ownership of the above. What is more, watermarks can also be the evidence in front of the court. In a word, digital watermarks can be an effective method to protect knowledge property and multimedia data.Watermarking algorithm, which includes watermark embedding and watermark extraction or detection, can be distinguished as blind detection watermarking and non-blind detection watermarking. This thesis starts with the mainframe of the digital watermarking system, and introduces the general methods of watermark embedding, watermark detecting and watermarking system attacking. Then the emphases turn to the auihor's research and innovation of digital watermarking in the domain of discrete wavelet transform. Based on the previous work of others, the author has mainly researched the following aspects:1. Propose an algorithm of digital watermarking based on chaotic encryption and Human Visual System (HVS). We design a binary image watermarking signal and encrypt it by a chaotic sequence cipher first. Then according to HVS, each watermark bit is embedded into the important coefficients of each wavelet tree of the host image. Experimental results show that the watermark obtained is invisible as well as robust against noise and commonly used image processing approaches (especially. JPEG).2. Complete the embedding process in DWT domain by exploiting the characteristics of HVS, HVS derived from DWT is introduced to take into account HVS such as gray-level sensitivity, noise sensibility around edges and iso-frequency masking. All these characteristic models are used to serve as the factors of the weighing function. Some modifications are proposed to make it suitable to the computation of the maximum visually tolerable watennark energy.Digital watermarking is a new technology, which is related to communication and information technology, image and speech processing, signal detection and evaluation, mathematics, human audio and visual systems, and computer network and application etc. There is no complete theoretical framework yet, The emphasis of the research will still be on the robustness enhancement, copyright certification, rapid automatic network testament, audio and video watermark, and it will be combined compactly with data encryption techniques, particularly the research on robustness and certification. The robustness of watermark is testified by its survival ability in data files. Most current algorithms have robustness to some extent, but all those robustness will be lost if various attacking methods are combined. How to find a more robust algorithm is still an urgent need at present. However, all the watermarking algorithms are not faultless more or less in some aspect such as providing trustful certification of copyright, so the algorithm of watermarking is and undoubtedly will still be one of the most important topics for the researchers all over the world.