Research Of Digital Image Watermarking Algorithm Based On Wavelet Transform

With the rapid growth of Internet and networks technique, Multimedia data transforming and sharing is common to many people. Multimedia data is easily copied and modified, so necessity for copyright protection is increasing. Digital watermarking has been proposed as technique for copyright protection of multimedia data. Watermarking is the process of embedding hidden copyright information into multimedia data by making small modifications on the data. In general, it is required that the embedded watermark should be not only transparent to human observers, but also robust enough so that it cannot be destroyed or removed after some processing or attacks.Firstly, this paper make a recapitulative summarize and analysis for the basic knowledge of digital watermarking technology from its origin, basic character, sort, common model, main application field and so on.Secondly, this paper introduces wavelet transform definition, wavelet transform characteristics, two-dimensional wavelet decomposability of image, Mallat algorithm and the application of wavelet transform.Following two novel robust wavelet based grayscale logo watermarking technique are presented in this paper. The first method is a wavelet-based FfVS characteristic watermarking algorithm. This algorithm is proposed in the paper and watermarks were embedding and extraction in the low-frequency sub-band after multi-resolution decomposition. Instead of using a random sequence, a visually meaningful gray scale logo is used as watermark which is scrambled by Arnold transform. The method uses the characteristic of Human Visual System (HVS) to enhance the robustness of the watermark and avoids the perceptibility of human eyes. The other watermarking algorithm based on discrete wavelet transform (DWT) of image and singular value decomposition (SVD) is presented. After decomposing the original image into four bands, the SVD is applied to the blocks of the low sub-band. To improve the security the watermark is scrambled by Arnold transform, and then is embedded into the largest singular value of every block. The watermark can be extracted without the original image, among which a person who does not know the secret key cannot correctly retrieve the watermark. Experimental results indicate that the performance of the proposed watermarking algorithm is invisible, robust and secure.