The DWT-based Digital Watermarking Method

At present, digital watermarking technology is a new sort of copyright protection technology, and it can be extensively used in the fields of digital work copyright protection, convert communication and the bill guard against falseness in commercial transaction and e-commerce etc.Nowadays, the methods of the research of digital watermark chiefly concentrate on the hiding in time domain, space domain and transform domain, in addition, there is the digital watermarking algorithm based on the file format and carrier formation technology.DWT is a kind of effective new method after Fourier transfonn in the field of the watermarking research. . Chiefly there are several kinds of methods in adding digital watermark into the DWT domain: (1) The multi-yardstick watermarking technology which is based on the DWT (2) The digital watermarking algorithm which is based on wavelet lifting (3) The sensitive watermarking algorithm which can certify the distortion of stationary image (4) Embedding many kinds of watermark at the same time which is based on integer waveletAt present, the usefulness of digital watermark generally is two aspects:(1) Hiding secret and individual information to protect die copyright of works.(2)Proving the reliability of works, or in other words, the source of content, the content authenticityand data completeness, which is also called interference certification (to prove whether there isinterference or distortion).The watermarking technology discussed in mis paper is fit for the application in the second aspect, and it makes it if the signals added watermarking have any change, the detected watermark won't be constant with the previous one, thus we can point out the occurrence of interference and distortion.The contribution of this thesis is following:1. Taking advantage of the feature of wavelet and human eyes' visual mask to do separate DWT to primary image and watermark by combining the original image and detail subgraph of the watermarking image in the same direction. The thesis presents a scheme of watermarking technique which embeds the watermark in image based on the wavelet multi-resolution.2. Analyzing the influence of the intensity of digital watermark's embedded into the primary image. Generally speaking. If the a value is great, the watermarking is stable, but the influence to the primary image is obvious, in other words, the watermark's visual imperception is bad; On the contrary, if the a value is small, the watermark's visual imperception is good, but the robustness of the watermarking is worse. Considering the requirement of watermark's robustness and imperception, we present a method which can definite the intensity of the image embedded by digital watermark by the content of image. Taking Lena image for example, we give out a method to select the a value.3. For the method's performance evaluation ,we sharpen, filter, enlarge and shirk the image, add chirp, change the balance and so on, to detect whether the image is attacked or/and distorted, and robustness of the watermark which is embedded by this scheme.