| With the rapid development of network communication and multimedia technology,digital image,audio,video and 2D vector graphics etc have become an important means of communication among humans.As a special kind of vector graphics,2D CAD engineering graphics has been widely used in mechanical design and other fields because of its powerful visual editing functions,high accuracy data,losslessly scaling ability and easy to saving and transmission.As an important technology of information security,digital watermarking has made certain progress in the fields of vector graphics copyright protection.Due to the special accuracy requirement of the engineering graphics,any minor modification to the data may cause serious consequences.Traditional digital watermark techniques,to a certain extent,would cause permanent distortion to the host,so they cannot be applied to some applications which have restrict requirements on data authenticity and precision.Fortunately,reversible watermarking is proposed to meet the needs of these applications.It can completely recover the original data after the watermark extraction and has no negative effect to the availability of original carrier.For strict technical requirements of 2D CAD engineering graphics,the reversible watermarking technology is definitely a good choice.This thesis first introduced the research background and current research status of 2D CAD engineering graphics watermarking technology at home and abroad,and then expounded the existed defects of the reversible watermarking on 2D CAD engineering graphics,summarized the main works of this paper.Subsequently,systematically introduced the relevant theoretical knowledge of reversible watermarking,including the frame and principle,characteristics and classic algorithms,etc.Finally,based on the current development status of the reversible watermarking technology,two reversible watermarking schemes used for content authentication were proposed.The main work includes:(1)Aim to authenticate the integrity of 2D CAD engineering graphics,two schemes Asym_HSC and Asym_HSP based on asymmetric histogram shifting and complementary embedding are proposed.Based on the correlation of the adjacent coordinates and phases,multiple prediction errors are obtained,and then asymmetric histograms are constructed by properly selecting prediction errors,respectively.The proposed schemes have great potential to be applied for content authentication of 2D CAD engineering graphics.(2)A novel reversible watermarking method based on 2D CAD engineering graphics is proposed in this chapter.Due to the low correlation of the engineering graphics vertices,two neighboring virtual coordinates are calculated for each vertex coordinate to achieve high correlation.With the idea of iterative embedding,high embedding capacity and good visual quality can be obtained after watermark embedding.Firstly,intervals with the same distance are divided based on the range of the distribution of the coordinates on each axis,and two neighboring virtual coordinates of each coordinate are calculated according to the ordinal number of the corresponding interval.Then the coordinate and its neighboring virtual coordinates are sorted to get an ordered data set.Experimental results and analysis show that it can effectively resolve the issues such as low capacity and poor visual quality in 2D CAD engineering graphics,and it is well suitable for host with low correction and high data precision requirements.(3)To verify the validity of the proposed algorithms,a watermarking authentication system for 2D CAD engineering graphics is designed and implemented.The reversible watermarking algorithm proposed in this thesis overcame the problem that traditional reversible watermarking technology request watermark carrier must with high data correlation,which can be applied for the copyright protection and content authentication of 2D CAD engineering graphics even with low data relevance. |
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