Reseach On Image Watermarking Algorithm Based On CDMA

Digital watermarking technology is a branch of information hiding technology. It is an effective means to solve the problems of information security and copyright protection of digital media. Recently, digital watermarking technology, especially watermarking technology for colorful image has attracted great attention. It has been extensive researched and applied in many fields. As a new means of communication, spread spectrum communication has developed rapidly in recent years. CDMA (Code Division Multiple Access), the third-generation in wireless communication technology, has good security property and anti-jamming capability. As the similarity between watermarking channel and communication channel, CDMA can be introduced into digital watermarking technology when embedding information into digital media. Experiments show that this is a practical and effective method. This thesis researches on CDMA-based digital watermarking for colorful image.The research background and current situation of digital watermarking is firstly given. This thesis summarizes the concept, the basic features, and the application fields of digital watermarking technology. After analyzed the typical algorithms in digital watermarking technology, this thesis focuses on some kinds of algorithms in transform domain. Then, a variety of common classification and common standards for evaluation in digital watermarking has been studied. Then this thesis introduces the theoretical basis and the basic model in spread spectrum communication technology, and focuses on some kinds of pseudo-random code sequence used in the spread spectrum communication technology. Furthermore, this thesis gives an overview of the advantages and the disadvantages of each code sequence and finally selectes Walsh code sequence as the orthogonal code sequence. This thesis also makes a recapitulative summarize and analysis on the basic knowledge of the two-dimensional discrete cosine transform (DCT) from its principles, nature and application in digital watermarking and so on. The size and location of the embedded DCT-block is fully discussed. Additionally, the color space is investigated and the RGB space is selected to embed more watermark information.A watermarking algorithm for colorful image is proposed. As "sync" problem isn't exist in digital watermarking and in order to easily carry out in computer, this thesis selectes Walsh code as the orthogonal spreading codes to orthogonal the watermark information in CDMA spread spectrum processing. The B part of the original colorful image is divided into 8×8 blocks and DCT transform is did on each block. Then the watermark information is embedded into the intermediate frequency coefficients. Experiments show that this algorithm has good invisibility and robustness.Then this thesis proposes a watermarking algorithm based on CDMA and HVS (Human Visual System). Based on the previous algorithm, this algorithm takes the characteristics of human visual system (HVS) into account when embedding watermark information. The application of HVS model in the process of watermark embedding can improve the invisibility and the capacity of the watermark. The HVS visual model, especially the Watson visual model used in this algorithm is studied in detail. The algorithm is based on RGB color space and uses Watson visual model. At last, image with watermark is attacked in several ways to validate this algorithm, such as cropping, scaling, noise, JPEG compression. The results show that this algorithm is good in visibility and robustness and can resist many types of conventional image process and malicious attacks.