Research Of Color Image Digital Watermarking Algorithm Based On DWT

Computer network communication technology, especially the development of Internet makes the exchange and transmission of data easier. With electronic equipments, such as computers, digital scanners, printers and so on, people can send digital information all over the world easily and quickly. The digitalized information media and the development of network make people pay more attention to the security of digital media. Digital watermarking technology is developing rapidly under this circumstance. Digital watermarking is a technology which embeds the specific meaning information into the multimedia products with a given algorithm. It is an effective means to achieve the protection and authentication of the digital products.Nowadays there are many ways to embed and extract digital watermarking, they mainly focus on spatial domain and transform domain. Spatial domain watermarking is realized by modifying the intensity value or gray value of the image pixel. As this algorithm does not need to transform the original image, this algorithm is simple and efficient. However, it is difficult to resist common image attacks and noise jamming and has less robustness. Transform domain watermarking firstly transform original image and then modify the coefficients to embed watermark. This kind of transformation includes Discrete Fourier Transform (DFT),Discrete Cosine Transform(DCT),Discrete Wavelet Transform (DWT) and so on. This method needs to transform the original image and the calculation is more complex. But the digital watermarking algorithm on transform domain can resist compression and low pass filter's effect. Furthermore it can resist common attacks such as JPEG compression, rotation and scaling. Besides it can easily combine with human visual system (HVS) to determine the combined strength of the watermarking embedding. In conclusion, watermarking method based on transform domain has more advantages. So it is more suitable for digital watermarking technology. On the basis of previous researches, the concrete research work and innovation of this paper can be described as follows:Firstly, this paper makes a recapitulative summarize on the basic knowledge of digital watermarking from its concept, principles, nature and application and so on.Secondly, this paper describes the methods to embed the digital watermarking. These methods mainly include the spatial domain and transform domain methods. Then this paper simply analyzes the principles and advantages and disadvantages of the spatial domain and transform domain and describes DFT, DCT and DWT in detail. In addition, emulation experiments about algorithm based on LSB,DCT and DWT is given. And after all this analysis and compare, this paper finally chooses DWT as the basic method.The paper introduces the basic thought and principle of the image permutation technology, and chooses the Arnold transform as the permutation encryption method. Experiments show the pretreatment before watermark embedding can not only enhance the security, but also improve the robustness of watermark.Lastly, draw on the existing research results, this paper proposes a digital watermarking algorithm based on DWT. This algorithm which embeds a color watermark image into the color carrier image expands the scope of application of the watermark. Before embedding we analyze the energy of green component of the watermark image, and then embed the watermark image depends on different situation, which can further improve the invisible and robustness of the watermark system.Plentiful emulation experiments show that this algorithm can ensure invisibility and robustness of the watermarking. And it has well robust for familiar image processing such as JPEG compression, noise contamination, cropping and fuzzy etc. Finally, we review the whole work, and make the expectation for the future research.