Research On Digital Watermarking Technology For Images Based On Discrete Wavelet Transform

With the rapid development of the internet, various kinds of digital multimedia information have widely distributed through network such as text, image, audio and video etc. But the information on internet can be easily duplicated and modified. So the copyright infringing problem on internet is becoming more and more serious. How to provide copyright protection has drawn extensive attention in recent years. To solve this problem the digital watermarking technique has been investigated.Digital watermarking technique, which embeds special information into digital products, is a new method for copyright protection with the help of digital watermark, we can prove the originator's owner to digital products that he creates, and the watermark can be the proof of anthentication and prosecuting illegal copyright infringing. Basically, there are two common methods of digital watermarking technique: spatial domain methods and transform domain methods. Spatial domain techniques are easy ways to embed information, but they are highly vulnerable to even small cover modifications. In many cases even the small changes resulting out of lossy compressinon systems yield to total information loss. Transform doman methods hide watermark in significant areas of the host image that makes them more robust to attacks, such as compression, cropping, and some other image processing, than the spatial methods. In fact, these kinds of algorithms are not only robust to various kinds of signal processing but also remain imperceptible to human sensory system. There are two main transform domain methods, one is to use the discrete cosine transform (DCT), the other is the use of discrete wavelet transform (DWT). In this paper, we mainly discuss the digital watermarking algorithms in wavelet domain.The major research works and innovatory points in this thesis are as follows:1. Investigate the basic principles and characteristic of digital watermarking technique,introduce the research backgrounds, basic principles, application areas, and recent development and the future of the digital watermarking technology.2. Analyze the algorithm of Mallat and the concept, characteristic of wavelet transform which includes the continuous wavelet transform and the discrete wavelet transform, point out the advantages of using wavelet transform in digital watermarking and mufti-resolution analysis.3. The pre-processing technique of watermarking is studied, especially the arnold transformation and the transformation period of 2-D arnold under different number is reached. 4. A method is proposed to analyze all levels coefficients of wavelet. The important subband sequence of wavelet images is figured out by comparing energy, mean value and mean-square deviation of subimages. We also analyze the energy diagram of image which is processed by the discrete cosine transformation in order to find the best position of watermark embedding.5. A new meaningful digital watermarking algorithm for images is presented, which is based on discrete wavelet transform and discrete cosine transformation domain. The meaningful digital watermark is more readable, practical and intuitional to compare with the traditional pseudo random sequences. Making use of masking peculiarity of human visual system, the watermark image is adaptively embeded into the blocked lowest approximation components of the gray image on DCT embedding technology, while most of other DWT methods embed watermark into the middle or high frequency components. And before embedding, the watermark picture is processed, which is to enhance the robustness of the watermark. Experimental results show that the proposed algorithm keeps the quality of the image well and is robust enough to JPEG compression, noise, filtering, image scaling, image enhancement etc.The outstanding characteristic in watermark technology is to ensure the quality of the watermarked image and to ensure that the watermark can be well extracted after many attacks. Basing on this consideration, we first analyze all levels coefficients of wavelet and propose a new method of computing the coefficients, then propose a new meaningful digital watermarking algorithm for images is presented, which is based on discrete wavelet transform and discrete cosine transformation domain. Therefore, it is meaningful in theory and practice.