Research On The Algorithms Of Semi-Fragile Reversible Watermarking Of 2-Dimentional Engineering Graphics

With the rapid development of digital technology and multimedia network,much attention has been paid to the information security of the data transported over the network.Among these existing security mechanisms,watermarking technology has been widely used for copyright protection,content authentication and secret communication,etc.2D CAD engineering graphics is a kind of vector graphics,and it has been widely used in engineering design due to its high precision,scaling invariant and easy storage.Nevertheless,copyright violations and unauthorized tampering are becoming outstanding issues of 2D CAD engineering graphics in nowadays.As an effective method for the protection of copyright and content authenticity,digital watermarking has been developed for 2D CAD engineering graphics.As for some traditional watermarking schemes,they generally produce permanent distortion in the host,so they cannot meet the needs of some applications which have restrict requirements on data precision and authenticity.Fortunately,reversible watermarking techniques are proposed to meet the demand of these situations.Since digital media is easy to be edited and tampered,therefore,fragile watermark is ususlly used for the integrity of graphics.This thesis first introduced the current research situation of digital watermarking technology,and then systematically elaborated the relevant theoretical knowledge of digital watermarking,including the frame and principle of watermarking,and the related works in reversible watermarking and fragile watermarking,etc.After deeply analyzing the current research states and existed defects on reversible watermarking and fragile watermarking of 2D CAD engineering graphics,three reversible watermarking algorithms used for content authentication are proposed.The main works of the thesis include:A semi-fragile reversible watermarking algorithm with accurate tampering localization is proposed.Firstly,all vertices in the 2D CAD engineering graphics are extracted and partitioned into groups.After that,the relative distance of these vertices are calculated,and the assigned grouping number is used as watermark.Finally,the watermark is embedded into the factor of relative distance by using an improved difference expansion transform.Experimental results and analysis show that the proposed algorithm can obtain a large capacity,good invisibility,and robust against translation,rotation,and even scaling.At the same time,it can detect some malicious attacks such as entity modification,addition and deletion,and can locate the tampering areas with a high precision.According to the characteristics of the coordinates and phases in 2D CAD engineering graphics,difference histograms are constructed.Consequently,two reversible watermarking schemes based on difference histogram shifting are put forward.The first scheme HS_C implements the integer part of coordinate values to construct the adjacent difference histogram and hides messages in the peak and zero point pairs.The scheme can achieve high capacity and good invisibility in the graphics with high correlated coordinates.Instead of coordinates,the second scheme HS_P adopts the integer part of phase value as the cover data,and the watermark is embedded by shifting and modifying the difference histogram of phase.It is robust against translation,rotation and even scaling.To verify the validity of the proposed algorithms,a watermarking authentication system for two-dimensional CAD engineering graphics is designed and implemented.The proposed watermarking algorithms not only can lossless restore the original vector graphics,but also can verify the integrity of graphical content to a certain extent.It is well suited for the applications with high data accuracy.