Research On Digital Watermarking Based On Fountain Code And Spread Spectrum Technology

With the rapid development of digital information technology,the operation of multimedia digital information destruction and unauthorized copying becomes easier.Digital image is widely used as a carrier of information in the Internet,its security and copyright protection problems need to be solved.Digital image watermarking technology is an important method to solve this problem.The robustness and the imperceptibility and the watermark embedding capacity are three important performance indexes of watermarking system,as there is a similarity between the important performance indexes of watermarking system and the validity and reliability of communication system,the application of channel coding and spread spectrum technology to digital watermarking system can effectively improve its performance.In this thesis,the fountain code and the CDMA spread spectrum technology are applied to the watermarking system to solve the problem that the high decoding complexity and poor adaptability to time-varying channel of traditional channel code using in watermarking system.The main contents are as follows:1.Firstly,this thesis expounds the basic theory of watermarking technology,includes the development and the system framework of digital watermarking technology,and summarizes the common watermarking attack types and performance indicators.Then the typical algorithm of watermark generation,embedding and detection technology is introduced,emphatically analyzes the theory of spread spectrum technology applied to watermarking system and the selection of spread code and the generation method of spread watermark in detail.2.The principle of encoding and decoding of LT code and the influence of degree distribution on decoding performance are studied.First,the definition and coding principle of fountain code are introduced,and the influence of several kinds of classical degree distribution and switching degree distribution on decoding performance is studied;then the procedure of design DRS degree distribution with decreasing ripple size is analyzed in detail,in order to reduce the necessary overhead.In view of the problem that the decoding rate of LT code with the above degree distribution is low at the initial decoding step,an improved switch degree distribution is proposed,and simulation to verify its decoding performance.3.In order to further improve the robustness and the watermark embedding capacity of watermarking system using channel coding and spread spectrum technology,a digital image watermarking blind algorithm based on LT code and CDMA spread spectrum technology is proposed.The algorithm encodes the original watermark with LT code,and then adopting CDMA spread spectrum technology for the purpose of generating the encoded watermark information.The encoded watermark information is embedded in the DCT domain of the carrier image.The influence on the robustness of the watermarking system with different degree distribution is studied;then the simulation of robustness performance between the proposed algorithm and the pseudo-random sequence spread algorithm and the LDPC coding algorithm under the common attacks is compared.The simulation results show that the scheme proposed has good invisibility and better robustness,and it also has good robustness when the amount of watermark embedding is large,which verifies the effectiveness of the proposed scheme.