1、天津工业大学本科毕业论文 外文资料 Information Hiding Thieoretic Research Based on Digital Watermark Technology School of Mathematics and Computer Science Ningxia Universit Yinchuan, China Abstract-With rapidly growing interest in ways to hide information, a large number of schemes have been proposed for audio and o
2、ther multimedia in digital pictures, video, audio and other multimedia objects.In an attempt to overcome this problem, watermarking has been suggested in the literrature as the most effective means for copyright protection and authentication .The main focus of this thesis is the problem of watermark
3、ing and compression of image due to bandwidth or storage constraints. Keywords: information hiding； digital watermarking； transparency； robustness I. Introduction Due to the rapidly development of the Interest and the World-Wide-Web(WWW),distribution of digital multimedia data to a large population
4、of users can be done very easily.Moreover,digital data can be duplicated very fast and without any degration in quality-cinsider,forexample,how common the copying of musical CDs has become in the last few years.Naturally,this situation has raised many concerns about possible violations of intellectu
5、al property rights.Unauthorized duplication and distribution of copyrighted material(photographs,music,movies,etc.),without appropriate compensation to the copyright holders,are becoming increasingly problemtic.In order to fight piracy,many companies(especially in the entertainment and news industri
6、es)have devoted considerable attention to the development of information hiding (or watermarking)techniques.In plain terms,a watermark is a signal which is hiden inside some multimedia data,and carries information about this data(e.g.,owner,title,data of creation,ect).Thus a watermark uniquely ident
7、ifies the work being protected,and helps resolve disputes about the ownership of the data. There have been many instances of disputes or litigations on the intellectual ownership of multimedia data.A copyright violations lawsuit that received extensive publicity in the early 2000s,was that against N
8、apster.And the Digital Video Disk,also known as Digital Versatile Disk(DVD)consortium called for proposals for a copyright marking scheme to enforce serial copy management.The idea is that the DVD players sold to consumers will 天津工业大学本科毕业论文 allow unlimited copying of home videos and time-shifted vie
9、wing of TV programmers,but cannot easily be abused for commercial priacy.Electronic copyright management schemes have also been proposed by European projects such as Imprimatur and CITED,and American projects such as the proposed by the Working Group on Intellectual Property Rights. Due to its signi
10、ficance,the watermarking field has grown tremendously in the information hiding theoretic.There are numerous articles(the references therein)and books that explain the basic of watermarking,explore its many practical application,and evaluate the performance of various schemes under a variety of atta
11、cks. II. Digital Watermarking System A. Watermarking In the communication model for watermarking,the watermark embedder plays the role of the transmitter,the watermark detector plays the role of reciever and the attack represents the communication channel(Fig.1).The objective is to decode the hidden
12、 message reliably；the original image can be construed of as side information which is always available at the encoder,but is only available at the decoder in the private scenario(not the public one). In this paper, a transmitter sends a signal Xn to a receive (with n transmissions), through 天津工业大学本科
13、毕业论文 the following channel: Y=Xn+Sn+Zn, where Sn, Zn are independent, i.i.d.Gaussian random vectors.Here, Sn is known to the encoder, while Zn acts as noise known to neither encoder or decoder.It is proved that the capacity of this channel is the same as if Sn were known to the decoderas well. In ge
14、neral,this number grows linearly with the image size,and the constant of proportionality is known as the capacity C.Practical watermarking implementation embed at a rate R bits/image dimension,where RC.Namely,C=1/2 log（ 1+P/N） ,where P is the average（ per symbol） power of Xn and N is average of Zn.T
15、his result is quite surprising because one would expect Sn to act as inteference at the receiver,thushidering the detection scenario,Sn would play the role of the covertext（ known to the watermark embedder only),Xn would represent the watermark embedded, and Zn would be the noise added by the attack
16、er. B. Characteristics of watermarking In the design of watermarking schemes,we mainly think about two key requirements. Transparency: The hidden message should not interfere perceptually with the host signal.This requirement is perfectly justified by the fact that watermarking aims at protecting mu
17、ltimedia data,which are sensitive,ingeneral,tochanges.In other words,an image or a musical piece could become useless if the introduced artifacts（ due to watermarking） exceeded some perceptual threshold.The quality of the watermarked data must thus be comparable to that of the covertext,a requiremen
18、t which is often expressed in terms of a distorition constraint. Robustness: The message must be detectable in the watermarked image（ the covertext is assumed to be an image throughout this thesis,though similar techniques can be applied to other types of multimedia data） ,even after degradation duo
19、 to malicious attacks or other processing（ quantization,D/A conversion,etc） .Of course,detectability of the watermark is closely related to the maxinum amount of distortion that can be introduced by an attacker.A watermarking scheme is robust if it allows the hidden message to be accurately decoded
20、in a distorted image whose quality is close to that of the watermarked image（ this requriement is again expressed in terms of a distortion constraint） . C. Detection scenarios There are two decetionscenarios:private and public.In the private decetionscenario,the original image is available to the de
21、cetor,in the public scenario,it is not.Although public detection scheme can be more useful in practice(since it is not always possible to have the original image availableduring the decetion),private schemes usually offer more robustness. III. Watermarking Rates In The Presence Of Memoryless Attacks And Gaussian
