The Application Of Fountain Code In Digital Watermarking System Research

The development of the Internet gives convenience to the transmission and replication of the multimedia. But the security during the process of transmitting and replicating is should be reckoned with. Digital watermarking technology provides a guarantee to the safely transmitting and copyright certification of the multimedia. At present, how to improve the practicability of digital watermarking technology in different environment has been an urgent problem. As there is similarity between digital watermark system and communication system, some researchers research the digital watermark system by using the method in communication theory currently. The channel coding has been certified that it can improve the robustness of the digital watermark system effectively.This thesis mainly studies the application of the fountain code in digital watermarking system, the main contents are as follows:(1) First, this thesis expounds the basic theory of digital watermarking system, emphatically introduces the typical algorithm of watermark generation, embedding, detection and extraction, which can provide the reference to the use of fountain code in digital watermark system.(2) It introduces the encoding and decoding theories and procedures of LT code in detail. The influence of several kinds of degree distribution function on decoding success probability is studied. The decoding success probability under different decoding overhead and the time complexity of BP decoding and GE decoding are compared and analyzed. Through analyzing the residual translatability of BP decoding, here gives an improved BP decoding algorithm according to degree of 2 coded packages to improve the decoding success probability. The decoding rate of BP decoding scheme and the improved BP decoding scheme under three degree distribution functions is emphatically analyzed, and it lays a theoretical basis on subsequent application in digital watermarking system.(3) This thesis proposes a new algorithm based on LT code and a double pseudo-random sequence spread spectrum to improve robustness of the watermark in digital watermarking system. The watermark is encoded by LT technique and then spread spectrum using the pseudo-sequence, then embedded in the discrete cosine transformation(DCT) coefficients. It put the RSD-BP decoding scheme, RSD-improved BP decoding scheme and binary exponential-BP decoding scheme that have higher decoding rate into the application in digital watermarking system respectively. Then gives the simulation of robustness performance under JPEG compression attack, cropping attack, filtering attack, salt and pepper noise. The thesis also gives the comparison between LT coding scheme, no coding scheme and LDPC coding scheme, so as to verify the effectiveness of the proposed scheme.