Research On Reversible Image Watermarking Schemes

Digital watermarking embeds some signature information into digital multimedia by means of signal processing. The embedded messages are usually invisible. Digital watermarking plays a key role in the applications of copyright protection, content authentication and fake defending.Digital watermarking embeds data into cover images by modifying the value of original images, which may bring some imperceptible or permanent distortions to the cover image. Some special applications require the images keep high visual quality, such as law enforcement, medical and military system. These kinds of images can not tolerate any distortions due to the watermark, so reversible watermarking is proposed to solve this problem. Reversible watermark is called lossless watermark or erasable watermark, which means the original image can be restored losslessly after the watermark is extracted.First we introduce the history, research background, mathematical model, classification and the performance requirements in different condition of digital watermarking. Then we discuss the research background and the research focus of reversible watermark. This dissertation gives more attentions to a new reversible watermarking algorithm considering the characteristics of human eyes, and the reversible watermarking algorithms for JPEG images.The main contributions can be summarized as follows:1. A reversible watermarking algorithm based on HVS is proposed. Our human eyes are less sensitive to the changes in the rough area, but take notices of slight changes in smooth areas. Based on the characteristics of HVS, the proposed algorithm improves the efficiency of sorting and has priority to use the pixel block located in rough areas to embed the watermark, which can ensure low distortions and high visual quality.2. For JPEG image is widely used in our lives, a new code mapping method based on sorting is proposed to embed the watermark in JPEG bitstream directly. The proposed algorithm enhances the embedding capacity by improving the use ratio of VLC, and ensures reversible embedding and unchanged file size.