The Study Of The Digital Watermarking Technology Based On Gray Image

With the development of multimedia and network techniques, the Copyright Protection of digital media is becoming more and more important. How to ensure the security of digital media has become the focus of research work all over the world. As a new method of Copyright Protection, digital watermarking technique has attracted more and more attention of researchers and users since it was proposed in 1990s. More and more research results are obtained. However, technology of digital watermarking is still in its infancy, and there are still many problems to settle.In this dissertation, we study gray image digital watermarking. The main contributions are as follows:(1) The basic theories of digital watermarking technique are analyzed. Also we summarize the techniques of digital image scrambling, Discrete Cosine Transformation (DCT) and Discrete Wavelet Transformation (DWT) etc.(2) A new algorithm of image digital watermarking based on chaotic encryption is proposed. In this algorithm, Chaotic sequences are used as cipher sequence to encrypt binary image for ensuring the security of watermark. Then the DCT blocks of original image are classified into five categories according to the visual masking and texture characteristics of Human Visual System (HVS). Consequently, watermark components with different strength are adaptively embedded into some mid-frequency coefficients of original image to ensuregood invisibility. The experimental results show that the watermark has a good robustness against Gaussian noise, Salt & Pepper noise, Low pass, crop, JPEG procession etc.(3) A new algorithm with gray image digital watermarking based on DWT is proposed. Firstly, the original image is scrambled by Arnold transformation before DWT. Secondly, some high frequency coefficients are selected (such as LH₃) to form a matrix. This matrix is processed by Singular Value Decomposition (SVD). Lastly, the gray watermark is embedded into diagonal matrix of SVD. This algorithm uses meaningful gray image as watermark, so it greatly increases the information embedded in this algorithm. The experimental results show that the watermark has better robustness against common attacks of image.