Research Of Digital Watermarking Algorithm Based On Wavelet Transform

With the rapid development of computer and network technology, the acquiration of digital multimedia information is becoming more easily, meanwhile, it is also more easily suffer the attacks such as illegal copying, fabricating, tampering, infringement etc, the conventional safety precautions which based on the cryptology did not have the ability equal to their ambition. In order to protect the digital product itself security as well as the owner's benefits, people put forward the digital watermarking technique. Digital watermarking is a technology which with the precondition of having no affection to the quality of the digital product, embedding the secret information into the digital product which can't be seen to attain the protection of digital product. Generally, it possesses three basic characters of imperceptibility, robustness and security.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 authentication and prosecuting illegal copyright infringing. Basically, there are two common methods of digital watermarking technique: spatial domain methods and transform domain methods. Spatial domain methods are simple, but they are highly vulnerable to even small cover modifications. In many cases even the small changes owning to lossy compression systems may yield to total information loss. Transform domain methods hide watermark information in the significant areas of the host image, so they are more robust to attacks, such as JPEG compression , noise contamination, cropping, zoom and circumrotate etc.In fact, these kinds of algorithms are not only robust to various signal processing but also remain imperceptible to human sensory system. There are three main transform domain methods: the DFT, the discrete cosine transform (DCT) and the discrete wavelet transform (DWT). The paper will focus on the wavelet domain, the major research works and initiative points in this article are as follows:Firstly, the paper makes a comprehensive introduction about the algorithms of digital watermarking which based on wavelet transform. At first the background, the development and the algorithm's actuality of digital watermarking is introduced, dissertate the digital watermarking about the basic concept and character, generic model, typical algorithms, classification, application domain, attack analysis and evaluation of performance are also introduced.Secondly, elaborating the theory of wavelet analysis, application of wavelet transform and image permutation. According to the analysis of wavelet transform coefficients, we obtain the energy distribution rule, also we may see that after wavelet transform, aiming at various of attacks,the influence on each subband is different.Doing careful research on digital watermark algorithm in wavelet domain. Elaborating three key technologies should be first solved in the embedding method: wavelet selection, wavelet coefficients selection as well as how to balance the robustness and the invisibility of the watermark using human visual characteristic, simultaneously, making thorough analysis of the embedding position, mainly involves the low frequency and the high frequency subbands.Put forward a digital watermark algorithm based on DWT.The watermark information is embedded through comparison method, and the watermark is extracted without original image, realizing blind extraction, the simulation experiment shows that this algorithm is more robust.Put forward a method using the two-value image which has special meaning as watermark information. This paper will select the symbol which is"Shandong Normal University"as the embedding watermark.Carrying through pretreatment to the watermark with image permutation before embedding, making it becomes disorderly information. In this way the watermark's security and imperceptibility will be strengthened. Comparing with the traditional ways which used pseudo-random sequence, the significance watermark is more readable, more practicable and more intuitively.Lastly, in view of the research results, this article proposes a self-reference digital watermark algorithm based on wavelet transform. Different from the traditional methods, which chose the low frequency, the intermediate frequency or the high frequency to carry out the watermark's embedding. This article revises the original image in wavelet domain; we obtain the self-reference image, and find the embedding position through comparing the difference between the original image and the self-reference image. The algorithm not only guarantees the watermark's invisibility, but also strengthens watermark's robustness.Plentiful emulation experiments show that the algorithm ensures the watermark's imperceptibility and robustness, and is also robust to familiar image processing such as JPEG compression , noise contamination, cropping, zoom and circumrotate etc. Finally, we review the entire work, and make the expectation of the direction for the future research of watermarking.