Research On Several Digital Image Watermarking Algorithms

The development of digital technology not only brings convenience to people, but also makes us involved with troubles of information security. Digital image is main content of multimedia, and its capture, modification and transmission become more and more easy. The authentication, integrity verification of digital images and the argument of copyright restrict the development of information technology in a certain extent. In order to meet the growing requirement of multimedia products'copyright protection, especially the copyright of digital images, and meet the special requirement of covert communication limited by using of traditional cipher technology, there is rapid devel-opment for the information hiding. This dissertation focuses on the digital watermarking technology in the field of information hiding, which is one of hot issues in information technology.After having read a great deal of papers, four aspects in the digital watermarking technology are studied, and they are image authentication algorithm, robust digital im-age watermarking algorithm, zero-bit watermarking algorithm and reversible data hid-ing algorithm. And several novel algorithms and models are proposed. The main achievements are shown as follows:1. Considering the conflict between watermark localization accuracy and security, two image authentication algorithms based on chaotic system are proposed. The circular structure built by cat mapping makes different blocks correlative for the watermarks embedding, which overcomes the problem of low localization accuracy in traditional one-to-one mapping algorithms. Logistic mapping with sensitive character to initial value is selected to construct the pseudorandom circular chain, and singular value de-composing is used to generate block watermarks, that make the proposed algorithm not only achieves high localization accuracy as block-independent algorithm, but also en-hances the security. Exchange of rows or columns will not alter singular value, and wa-termarks may be checked unsuccessfully if the watermarks are generated directed by singular value, that will result in low localization accuracy.2. To protect the copyright of digital images, two robust digital watermarking algo-rithms having good mathematic foundation are proposed. As one of optimization theory, support vector machine with good learning ability and generalization ability is used to build a relationship model between the target pixel and neighbor pixels by its regression theory, and watermarks are embedded by modifying the target pixels. QR decomposi-tion is introduced into digital watermarking technology. Watermarks can be embedded into the first column component of Q matrix due to the stability of Q matrix in QR de-composition. The two algorithms are blind methods, which can resist some distortions and have good robustness.3. To change the traditional way that embedded watermarking by modifying the content of host images, which induce irreversible distortion, a novel zero-bit water-marking algorithm based on singular value decomposition is proposed. The invariant characters of singular value decomposition make the first singular value generate the information of images. The binary watermark image is computed with information of images to generate authorized information saved at the registration center, and this method overcomes the shortcoming that the watermarks of existing zero-bit water-marking algorithms are invisible and meaningless. The relationship between water-marks capacity and security is also studied.4. In reversible data hiding algorithm, in order to mitigate the distortion between the modified pixels and original pixels in difference expansion scheme, Logarithm func-tion is used. In addition, the relationship of mean values between image blocks is used to design the rule of the classification of the image blocks and the rule of embedded di-rections, and the rules solve the problem that traditional methods only embedded the same amount data in single direction in each image blocks. Experimental results show that our method can increase the payload and provide high embedded image quality.The topic of this dissertation is in an interdisciplinary research area, which is part of image processing, information security, mathematics and so on. Some key problems in digital watermarking are solved, and the work will bring improvement of digital wa-termarking technology, and would promote the development of copyright protection of multimedia, especially digital images.This dissertation consists of 7 chapters, including 66 figures,11 tables, and 134 references.