Research On Blind Watermarking Scheme Of Digital Color Image

With the rapid development of computer technology and network technology, the digital products, e.g., digital color image, have been widely spread on the Internet, due to the characteristics of easily get and copy, which also makes the copyright protection of digital color image become more difficult and the piracy and copyright infringement become more and more serious. Therefore, whether using the color image as host image or as watermark image, the digital color image watermarking technology has already become one of the hot research fields and has been receiving more and more attention.By analyzing the features and limitations of some existing works, this thesis has proposed some novel blind-extraction-based watermarking methods by means of some advanced technologies of image transform and matrix decomposition, in which the watermark capacity, robustness, invisibility, and algorithm efficiency have been investigated, respectively. Moreover, a considerable of experiments have been provided to illustrate the performances of the proposed methods.The main contribution of this thesis is as follows:(1) By incorporating the advantages of spatial domain and transform domain, a new DCT-based blind color image watermarking algorithm in the spatial domain has been proposed. According to the generating principle and the distribution feature of Direct Current (DC) coefficient in DCT transformation, DC coefficients of each8X8block are directly calculated in spatial domain, and each watermark information bit is repeatedly embedded for four times by means of the coefficient quantization method. In this method, the watermark can be extracted from the watermarked image without the requirement of the original watermark or the original host image, and the final binary watermark is decided by the principles of first select the combination and majority vote. It has been shown from experimental results that the proposed method not only attains the higher robustness, but also has lower-computation complexity.(2) Aiming at the problem that color watermark image has more information bits and is not easily embedded, a novel dule color image blind watermarking algorithm has been proposed by utilizing state-coding and Integer Wavelet Transform (IWT). This method not only use the feature that the IWT does not exist rounding error, but also use the proposed state coding method that using the non-binary information to represent the watermark information. When embedding watermark, the state code of data set is modified to equal the hiding watermark information. Moreover, the rules of state coding are also used to extract watermark from the watermarked image without resorting to the original watermark or original host image. The simulation results show that the algorithm can embed high-capacity color watermark information into color host image.(3) In order to effectively enhance the invisibility of embedded color watermark, a SVD-based color image watermarking method has been proposed. When embedding watermark, the watermark bit is embedded into4×4block by modifying the second row first column and the third row first column elements of U component after SVD. Then, the embedded block is compensated by the proposed optimization operation. The embedded watermark is directly extracted from various attacked images by using the relation between the modified elements of U component without resorting to the original data. The experimental results show that the proposed algorithm not only overcomes the shortcoming of false positive detection, but also attains better invisibility.(4) Aiming at the problem that the color watermarking method has weak robust, a color image blind watermarking algorithm has been proposed, in which Schur decomposition has been utilized. Firstly, the theory of the Schur decomposition and the feature of decomposed image block are further analysized. Then, the relationship between the coefficients not only is modified to embed watermark, but also is used to blind extract watermark. Experimental results show that not only the invisibility of the proposed algorithm is ensured, but also the robustness is significantly enhanced.(5) Considering the problem that some existing color image watermaings need more times to work, an efficient color image blind watermarking algorithm based on QR decomposition has been proposed. Firstly, the color host image is divided to4X4non-overlapping pixel blocks. Then, each selected pixel block is decomposed by adopting QR decomposition, and the first row forth column element in the matrix R is quantified for embedding the watermark information. In the extraction procedure, the watermark can be extracted from the watermarked image without the original host image and the original watermark image. The simulation results show that the algorithm not only meet the requirements of the invisibility and robustness of the watermark performance, but also has high efficiency in computation complexity.