Research On Algorithms For Improving The Capacity Of Digital Watermarking

With the rapid development of network and computer technology in the recent years, digital watermarking has been a rising network information security technology and become a popular topic in network security domain. It holds wide application prospect in several domains, for example, copyright protection, information hiding and etc. The digital watermarking technology can prove the copyright and integrity of original data through embedding some cryptic information, that is, watermark in it, because watermark can endure some attacks, such as pirate and modification.There are many aspects to be noticed in watermarking design, for example, imperceptibility, robustness, security and capacity. Image watermarking capa- city is an evaluation how much informarion can be hidden in a digital image. Many researchers have been focusing on security and robustness, but rarely on the watermarking capacity. In fact, researching on the capacity has much meaning to design of watermarking.Taking the capacity as a clue and improving the capacity as a goal, this paper is mainly divided into three parts.Firstly, the communication system model of digital image watermarking is proposed by using its traditional one. Then the channel capacity of water- marking system is analyzed from the view of information theory. Maximum watermark image based on the content of image is cited into spatial and wavelet domains to calculate the capacity of a digital image watermarking. Experimental results show that the method is effective and feasible.Secondly, this paper tries to improve the capacity of watermarking with novel algorithms. After doing research on basic theories and typical algorithms, two algorithms for improving the capacity of watermarking are presented.From the angle of enhancing the capacity of one wavelet coefficient, one adaptive algorithm is presented. From the angle of increasing the number of embedded domains, another algorithm is given. Experimental results indicate that the two methods both have larger capacity and have their advantage and disadvantage in robustness and security.Finally, multi-watermark technology which is related to large capacity watermarking is studied and a blind multi-watermarking algorithm is presented. Comparing with the primary algorithm, it is validated its capacity and robust- ness. It can extract the watermark without original image, so it has its practical applications.