An Investigation Of Digital Watermarking Technique Based On The Combination Of WPT And DCT

The work of the dissertation focus mainly on Digital Watermarking basing onthe frequency domain of digital static image. Digital Watermarking is to determinethe ownership or examine the primitiveness of the digital product by inserting ainformation in it. The digital products include digital pictures, sound, documents,books, video etc. The information, or mark, is invisible or visible. As an importantbranch of Information Hiding, Digital Watermarking is one effective method for thedigital product copyright protection, communications security, data authenticationand access control and so on.As a new technology, Digital Watermarking appears in the 1990s. It can makeup the weakness of Digital Signature not being able to insert a massive informationin the primary data, and make up the flaw of Digital Label easily revised andrejected, and make up the limitation of Digital Fingerprint only being able toproduce the information of the copyright destroyer, and make up the insufficiencyof Password Technology not being able to provide further protects of the data afterbeing deciphered. As a beneficial supplement of the tradition information securityand the copyright protection system, Digital Watermarking research has animportant value on academic and practical applications.The main content of the dissertation are summed up as follows:InChapter 1, the basic concept of Information Hiding and DigitalWatermarking, and the relation of the both, and the significance of research onDigital Watermarking are briefly introduced.In Chapter 2, the background knowledge involved in the dissertation isintroduced, mainly including the theory and application of Digital Watermarking,the theories of discrete cosine transform and wavelet, the theory and application ofwavelet packet, and the theory of human visual system and so on.In Chapter 3, the domestic and foreign existing typical Digital Watermarkingalgorithms are analyzed. The algorithms are divided into: spatial domain algorithm,frequency domain algorithm, compression domain algorithm as well as robustnessalgorithm. Frequency domain algorithm is the hot spot which now the academicstudies and also is the key point in the dissertation. In the dissertation, the analysisand the comparison of the discrete cosine transform(DCT) domain and the waveletdomain typical algorithms are carried on.In Chapter 4, the robustness and invisibility of wavelet packet transform(WPT) and DCT based digital image watermarking are studied with emphasis. Anew method using the combination of WPT and DCT is proposed, then thesimulation experiment and the result analysis are carried on. The compoundtechnology of Digital Watermarking is the technology which unifies kinds ofwatermark technology together, making up the deficiencies by getting others'strong points, and increasing the robustness and invisibility of the embeddedwatermark. With the human visual system(HVS) and the combination of WPT andDCT, the algorithm adopts different methods to insert one watermark in the lowfrequency and high frequency of the host image wavelet packet decomposition(WPD) respectively. Considering the HVS and the DCT energy compression abilityand the ability of ridding correlation as well as the different anti-attack capabilitiesof the different wavelet packet frequency bands, the algorithm adopts differentmethods to insert one watermark in the low frequency and high frequency of thehost image WPD respectively.The method has the characteristics as follows: First, embedding a watermarkin the low and high frequency coefficients of the WPD respectively, fully using thedifferent anti-attack capabilities of the different wavelet packet frequency bands,may guarantee that we can still extract a ideal watermark from the watermarkedimage after encountering different attacks. Therefore, the algorithm has a betterrobustness and can adapt to more situations. Second, considering the HVS and theDCT energy compression ability and the ability of ridding correlation, the lowestfrequency band of the WPD has a further discrete cosine transform. Fully using theWPT and DCT different merits in processing signal, the watermark has a betteranti-attack capability and a good security. Third, the watermark is embedded in thetexture sub-blocks of certain high frequency sub-bands of the WPD, which enhancethe watermark invisibility. Fourth, embedding the watermark twice in the differentfrequencies of the host image makes the watermark capacity increased.Experimental results show that the algorithm has a better robustness and invisibility,and a large watermark capacity and a good serviceability.In the dissertation, the simulation experiments to the proposed algorithm arecarried on, which aims to prove the performance of the algorithm's invisibility androbustness to different attacks. Under the same experimental condition, the contrastanalysis of the algorithm and the other one is given. First, the watermark capacityof the algorithm is two times of the contrast one, but the proposed algorithm hashigher PSNR, watermark response value and good invisibility. Next, the algorithmhas a good robustness to the attacks such as JPEG compression, filtering, additivewhite noise, geometry cuts, resizing, contrast swelling, union attack and so on, butthe contrast algorithm fail to resist the attack of geometry cuts and has a worserobustness than the proposed algorithm to contrast swelling.In Chapter 5, a summary to the full text and a plan for next research are given.The main contribution of the dissertation lies in:1. Collect and reorganized lots of related literature and data material aboutDigital Watermarking.2. On studying the achievement of the predecessors, propose a kind of newcompound digital watermarking algorithm. The simulation experiment proves thatthe algorithm has a better robustness, invisibility and serviceability.