Research On Digital Watermarking Algorithms Of Images Based On DCT

The technology that takes digital watermarking technology as the main copyright protection of digital products is growing rapidly, which makes the research on watermarking technology become a hotspot in the field of information security. Whether a watermarking algorithm is excellent or not is decided directly by its performance to resist various common attacks. Therefore, to enhance the robustness of algorithm and to improve the transparency of algorithm to all kinds of attacks is the priority among priorities in the field of digital watermarking research.In this thesis, the present situation of image watermarking algorithm is firstly intensive studied. Then aiming at the problems existing in the present situation of image watermarking algorithm, such as the existing methods will seriously decrease the pixel quality of the original carrier image and they have weak ability to resist the common attacks. They are carried out by synthetically using the characteristics of the theory of MCA, RPCA and QR.The main research work of this thesis is as follows:(1) A digital watermarking algorithm based on MCA is proposed. Aiming at the problem that the quality of the image pixels is reduced or damaged and the robustness of the watermarking algorithm is not strong, the idea of hierarchical embedding is put forward. The original carrier image is divided into smooth layer and texture layer by MCA, which can reduce the effect of image pixels quality. Take DCT transform on the texture layer and choose the intermediate frequency part to embed watermark, which can improve the robustness of algorithm. The results of experiment illustrate that it is not only can obtain higher visual quality but also improve the resistance ability of cutting attacks in a certain extent effectively. At the same time, it outperforms in robustness, such as salt and pepper noise attacks and JPEG compression attacks.(2) A digital watermarking algorithm based on robust principal component analysis is proposed. Aiming at the problem that the algorithm (1) has yet to be strengthened to salt and pepper noise attacks and cutting attacks in a certain extent, an alternative hierarchical embedded watermarking algorithm is proposed combinng with RPCA. Take DCT transform on the texture layer and embed watermark. Then, embedded the watermarking in the part of intermediate frequency and merge the two layers to get the watermark image. The results of experiment illustrate that this method not only can obtain higher visual quality but also has stronger robustness than (1) against the cut attacks in a certain extent and salt and pepper noise attack.(3) A digital watermarking algorithm, which can against large area cropping attacks or wear attacks is proposed. Aiming at the problem that the resistance ability of most of the algorithms for large area of cutting attack or wear is either not strong or even do not, this thesis combines the high capacity and high error correcting capability of QR code and propose a new algorithm:Digital watermarking algorithm for QR code based on DCT and blocked images. This algorithm encodes secret information into QR code as watermark. The results illustrate that this algorithm can effectively resist more than 90% of the cropping attacks to the maximum extent. And with the increase of embedding frequency, the resistance to cutting attacks is stronger. At the same time, it has strong robustness and high transparency to resist the white noise and Gauss noise, salt and pepper noise with high noise density and JPEG compression attacks with high compression factor.