Research On Robust Image Watermarking Technology In Transform Domain

As information becomes a kind of important resource, information security plays significant role in a country's crucial domain. With the emergence of a set of powerful multimedia tools, digital image, which is the represent of multimedia information, is prone to be copied and tampered. Digital watermarking is considered as a brand-new research direction in information security area, which is a new technology that can hide and track information in network environment, and the traditional encryption and decryption system is short of this advantage. Robust watermarking provides an efficient way to protect image's copyright.Based on introducing digital image watermarking technology in detail, the dissertation analyzes several kinds of typical digital image watermarking algorithm, researches on the safety and the ability to resist geometric attack on the condition that satisfies imperceptibility. The major contributions in the dissertation are described as following:(1)To improve the security of watermarking system, spread spectrum watermarking algorithm in wavelet domain based compound chaotic sequence is put forward. The compound chaotic sequence is used as spread spectrum code to create spread spectrum watermark, and watermark is embedded into middle frequency coefficients of the wavelet domain through odd-even quantization. Spread spectrum watermarking technology enhances not only the security and robustness of watermark, but also realizes blind extraction.(2)Aimed at the disadvantage of representative watermarking algorithms based on SVD(singular value decomposition), a kind of robust watermarking algorithm based on SVD and geometrical correction is put forward. The optimization of quantization step is acquired by genetic algorithm, then watermark bits are embedded into first singular value of each block through quantization. While extracting the watermark, DFT(discrete fourier transform) and geometrical invariant moment are introduced to estimate geometrical transform and rectify the original image, then watermark is resumed by extracting algorithm. The stability of SVD and validity of geometrical coefficients estimation improve the performance of watermark.(3)On the basis of the research of digital watermarking and DRM(digital right management), a digital image copyright protecting system based on robust watermark is put forward. Designing the architecture and model of the system, describing the work flow of purchasing digital content and authenticating digital production, GUI(graphical user interface) design and realization of copyright serving center is carried out at lenth.