Research On Multi-purpose Watermarking Of Color Image Algorithm Based On Quaternion Domain

With the advent of the information age,the dissemination of pirated digital works has become more and more convenient and widespread on the Internet,thus leading to a serious issues of copyright protection.As a method of effectively protecting information security,digital watermarking has become a research focus in academia.However,the existing single digital watermark is generally only a single function of copyright protection or content authentication,for the reason that it will be more and more difficult to meet the complex and varied practical needs.Color images are taken as the research object,the thesis focuses on the digital watermarking algorithm based on color image.After studying of the robust watermarking with a function of copyright protection and the fragile watermarks with a function of content authentication,this thesis completes the following aspects of work.1.Based on the advantages of discrete wavelet transform,quaternion discrete cosine transform and singular value decomposition,a robust color image watermarking algorithm is proposed.Firstly,each channel of color image is preprocessed with discrete wavelet transform,and their low-frequency sub-bands are described as a quaternion matrix,then that quaternion matrix is made block quaternion discrete cosine transform.a coefficient matrix is constructed by the first component of the real part coefficients for each sub-block.Finally,the watermarks are embedded into the singular values of that coefficient matrix.Experiments show that the algorithm has good imperceptibility,and keeps robust to JPEG compression,multiple signal processing attacks and geometric attacks.2.Combining the coefficient characteristic of quaternion discrete cosine transform,a A self-embedding fragile watermarking algorithm of color image based on QDCT is proposed.Firstly,the color image is divided into 2?2 sub_blocks and preprocessed with the quaternion discrete cosine transform.Then,the characteristic fragile watermark is generated by the quaternion discrete cosine transform modulus coefficients,and then that characteristic fragile watermark is embedded into the least significant bit in the space domain.To constructing the multi-watermarking algorithm which has both copyright protection and tamper positioning function,this self-embedded fragile watermarking algorithm is combined with the above robust watermarking algorithm.Experiments show that the multi-watermarking algorithm has good image fidelity,and has accurate tampering and positioning ability for sub-channel tampering.The interaction between the fragile watermark and robust watermark is small.