Dissertations / Theses on the topic 'Spread Spectrum Audio Watermarking'

This Thesis deals with a method to enforce the intellectual property rights and protect digital media from tampering – Digital Audio Watermarking. The main aim of this work is implement an audio watermarking algorithm. The theoretical part defined basic terms, methods and processes, which are used in this area. The practical part shows a process of embedding the digital signature into a host signal and her backward extraction. The embedding rule used spread spectrum technique and a psychoacoustic model. The implemented psychoacoustic model involves two properties of the human auditory system which are frequency masking and representation the frequency scale on limited bands called critical bands. The model is relatively new and based on the DWPT. In terms of above model is then the digital watermark embedded in the wavelet domain. This algorithm is implemented in technical software MATLAB. One part of this work focuses on robustness tests of the algorithm. Common signal processing modifications are applied to the watermarked audio as follows: Cutting of the audio, re-sampling, lossy compression, filtering, equalization, modulation effects, noise addition. The last part of the thesis presents subjective and objective methods usable in order to judge the influence of watermarking embedding on the quality of audio tracks called transparency.

In this work is presented technique for embedding digital watermark in digital audio signals. Digital watermark must be imperceptible and should be robust against attacks and other types of distortion. Algorithm is implemented for embedding digital watermark using technique spread-spectrum and psychoacoustic model ISO-MPEG I layer I. Robustness was tested for filtering signal, MP3 compression and resample method.

Digital technologies know an unprecedented expansion in the last years. The consumer can now benefit from hardware and software which was considered state-of-the-art several years ago. The advantages offered by the digital technologies are major but the same digital technology opens the door for unlimited piracy. Copying an analogue VCR tape was certainly possible and relatively easy, in spite of various forms of protection, but due to the analogue environment, the subsequent copies had an inherent loss in quality. This was a natural way of limiting the multiple copying of a video material. With digital technology, this barrier disappears, being possible to make as many copies as desired, without any loss in quality whatsoever. Digital watermarking is one of the best available tools for fighting this threat. The aim of the present work was to develop a digital watermarking system compliant with the recommendations drawn by the EBU, for video broadcast monitoring. Since the watermark can be inserted in either spatial domain or transform domain, this aspect was investigated and led to the conclusion that wavelet transform is one of the best solutions available. Since watermarking is not an easy task, especially considering the robustness under various attacks several techniques were employed in order to increase the capacity/robustness of the system: spread-spectrum and modulation techniques to cast the watermark, powerful error correction to protect the mark, human visual models to insert a robust mark and to ensure its invisibility. The combination of these methods led to a major improvement, but yet the system wasn't robust to several important geometrical attacks. In order to achieve this last milestone, the system uses two distinct watermarks: a spatial domain reference watermark and the main watermark embedded in the wavelet domain. By using this reference watermark and techniques specific to image registration, the system is able to determine the parameters of the attack and revert it. Once the attack was reverted, the main watermark is recovered. The final result is a high capacity, blind DWr-based video watermarking system, robust to a wide range of attacks.

The explosion in stereoscopic video distribution increases the concerns over its copyright protection. Watermarking can be considered as the most flexible property right protection technology. The watermarking applicative issue is to reach the trade-off between the properties of transparency, robustness, data payload and computational cost. While the capturing and displaying of the 3D content are solely based on the two left/right views, some alternative representations, like the disparity maps should also be considered during transmission/storage. A specific study on the optimal (with respect to the above-mentioned properties) insertion domain is also required. The present thesis tackles the above-mentioned challenges. First, a new disparity map (3D video-New Three Step Search - 3DV-NTSS) is designed. The performances of the 3DV-NTSS were evaluated in terms of visual quality of the reconstructed image and computational cost. When compared with state of the art methods (NTSS and FS-MPEG) average gains of 2dB in PSNR and 0.1 in SSIM are obtained. The computational cost is reduced by average factors between 1.3 and 13. Second, a comparative study on the main classes of 2D inherited watermarking methods and on their related optimal insertion domains is carried out. Four insertion methods are considered; they belong to the SS, SI and hybrid (Fast-IProtect) families. The experiments brought to light that the Fast-IProtect performed in the new disparity map domain (3DV-NTSS) would be generic enough so as to serve a large variety of applications. The statistical relevance of the results is given by the 95% confidence limits and their underlying relative errors lower than er<0.1

Abstract The worldwide success of wireless communications was originally fueled by the possibility to replace existing cables with wireless solutions. This phenomenon imposed the development of security engineering as a multidisciplinary field. Although wireless solutions can reduce installation costs and allow introducing new services, the end–users expect it to have the same level of security as they would normally have with wired solutions. Secure communications is an important part of the overall security of industrial wireless communications systems (IWCS). The aim of this thesis is to develop new security engineering methodologies for IWCS. The author develops countermeasures against confidentiality and integrity attacks and carries out a security analysis covering the protocol, electromagnetic and physical layer. In the first part of the thesis, Host Identity Protocol (HIP) is utilized to secure communication in an intra–vehicular network. Simulations and measurement campaigns are also conducted to evaluate the impact of the overhead on security in a tunnel, considering line–of–sight (LOS) and non–LOS (NLOS) scenarios. Electromagnetic analysis (EMA) is an important step in the development of safety–related systems. Today, the increasing usage of smaller integrated circuit also increases the susceptibility to electromagnetic (EM) interference. From near–field (NF) to far–field (FF) transformation, a method for the evaluation of the emissions leakage is investigated. The virtual EM (VEM) interface of the device–under–test (DUT) is studied, and it is described how an adversary can exploit it for denial of service (DoS) attacks. An effective jamming attack model is studied, and the theoretical calculations are validated with experiment–based results. Finally, focusing attention on physical layer security, two algorithms are developed. Active radio frequency fingerprinting (RFF) implements the exchange of a public key during the setup of secure communication. Afterwards, utilizing a jamming receiver in conjunction with the spread spectrum (SS) watermarking technique, the watermark–based blind physical layer security (WBPLSec) protocol is presented. The analysis and results indicate how the WBPLSec seems to be a valuable technique for deploying physical layer security by creating a secure region around the receiver
Tiivistelmä Langattoman tietoliikenteen maailmanlaajuista suosiota kiihdytti alun perin mahdollisuus korvata tietoliikennejärjestelmissä käytetyt kaapelit langattomilla ratkaisuilla. Ilmiö lisäsi myös tarvetta kehittää alan turvatekniikkaa monialaisen tutkimuksen pohjalta. Vaikka langattomat ratkaisut merkitsevät pienempiä asennuskustannuksia ja tarjoavat mahdollisuuksia luoda uudenlaisia palveluja, järjestelmien loppukäyttäjät edellyttävät kuitenkin niiden turvallisuuden olevan vastaavalla tasolla kuin langallisissa verkoissa. Myös teollisuuden langattomien tietoliikennejärjestelmen turvallisuus riippuu pitkälti viestintäkanavien turvallisuudesta. Väitöksen tavoitteena on kehittää uusia menetelmiä, joilla teollisuuden langattomat tietoliikennejärjestelmät voitaisiin turvata. Väitöksessä kehitetään toimenpiteitä tietoliikennejärjestelmien luottamuksellisuuteen ja koskemattomuuteen kohdistuvia hyökkäyksiä vastaan ja toteutetaan turvallisuusarviointi, joka kattaa järjestelmän protokollakerroksen sekä sähkömagneettisen ja fyysisen kerroksen. Väitöksen ensimmäisessä osassa hyödynnetään HIP–protokollaa (Host Identity Protocol) liikennevälineen sisäisen tietoliikennejärjestelmän turvallisuuden varmistamisessa. Lisäksi siinä kuvataan simulaatiot ja mittaushankkeet, joiden tavoitteena on arvioida käytetyn protokollan turvallisuusvaikutuksia esteettömän (line–of–sight, LOS) ja esteellisen (non–line–of–sight, NLOS) näköyhteyden tapauksissa. Sähkömagneettinen analyysi on tärkeä vaihe turvajärjestelmien kehitysprosessissa. Järjestelmissä käytetään yhä enemmän pieniä integroituja piirejä, mikä voi myös altistaa ne sähkömagneettisille (electromagnetic, EM) häiriöille. Väitöksessä tutkitaan lähikenttä–kaukokenttä -muunnokseen perustuvan arviointimenetelmän avulla sähkömagneettisen vuotosäteilyn tasoa. Lisäksi perehdytään testattavan laitteen (device under test, DUT) virtuaaliseen EM–liitäntään ja kuvataan, miten vastaavaa liitäntää voidaan hyödyntää palvelunestohyökkäyksissä. Väitöksessä tutkitaan myös tehokasta häirintämallia ja validoidaan teoreettisten laskelmien tulokset kokeellisesti. Lopuksi väitöksessä keskitytään tietoliikennejärjestelmän fyysisen kerroksen turvallisuuteen ja kehitetään kaksi algoritmia. Aktiivisen radiotaajuisen tunnistusmenetelmän avulla voidaan vaihtaa julkisia avaimia turvallista tietoliikenneyhteyttä muodostettaessa. Lisäksi esitellään vesileimausmenetelmään perustuva fyysisen kerroksen salausmenetelmä, WBPLSec. WBPLSec luo vastaanottimen ympärille suoja–alueen, minkä ansiosta se vaikuttaa analyysin ja tutkimustulosten perusteella olevan tehokas menetelmä toteuttaa fyysisen kerroksen suojaus

Dans cette thèse, nous étudions dans une première partie l'impact de la contrainte de sécurité en tatouage. Dans le contexte WOA (Watermarked contents Only Attack), un adversaire possède plusieurs contenus tatoués et cherche à estimer la clé secrète d'insertion afin d'accéder aux messages cachés. Une nouvelle manière de tatouer en étalement de spectre est présentée ici. Celle-ci est basée sur la construction de distributions circulaires dans le sous-espace secret de tatouage. Cette technique permet de minimiser la distorsion en moyenne provoquée par l'ajout de la marque dans le contexte WOA en utilisant l'algorithme d'optimisation des Hongrois et la théorie du transport. Nous vérifions ensuite qu'un tatouage sûr est utilisable en pratique en prenant comme exemple le tatouage d'images naturelles. Dans une seconde partie, nous nous intéressons au cadre de l'estampillage d'oe uvres numériques permettant de tracer les redistributeurs de copies illégales. Les codes traçants utilisés sont ceux proposés par Gabor Tardos et sont résistants aux attaques de coalition, c'est-à-dire au groupement d'adversaires mettant en commun leurs contenus numériques afin de forger une version pirate. Puisque les techniques de tatouage permettent l'insertion de codes traçants dans un contenu numérique, nous avons conçu une attaque "au pire cas" qui dépend du niveau de sécurité et qui permet, pour les adversaires, de baisser leur accusation. Nous montrons que pour le cas particulier de l'estampillage un tatouage sûr sera plus efficace qu'un tatouage non-sûr (à robustesse équivalente). Finalement, une implantation des codes traçants dans un contenu vidéo utilisant des méthodes sûres par étalement de spectre est proposée. Nous montrons alors l'efficacité de l'accusation des adversaires dans ce cadre pratique.

Les systèmes dynamiques discrets, œuvrant en itérations chaotiques ou asynchrones, se sont avérés être des outils particulièrement intéressants à utiliser en sécurité informatique, grâce à leur comportement hautement imprévisible, obtenu sous certaines conditions. Ces itérations chaotiques satisfont les propriétés de chaos topologiques et peuvent être programmées de manière efficace. Dans l’état de l’art, elles ont montré tout leur intérêt au travers de schémas de tatouage numérique. Toutefois, malgré leurs multiples avantages, ces algorithmes existants ont révélé certaines limitations. Cette thèse a pour objectif de lever ces contraintes, en proposant de nouveaux processus susceptibles de s’appliquer à la fois au domaine du tatouage numérique et au domaine de la stéganographie. Nous avons donc étudié ces nouveaux schémas sur le double plan de la sécurité dans le cadre probabiliste. L’analyse de leur biveau de sécurité respectif a permis de dresser un comparatif avec les autres processus existants comme, par exemple, l’étalement de spectre. Des tests applicatifs ont été conduits pour stéganaliser des processus proposés et pour évaluer leur robustesse. Grâce aux résultats obtenus, nous avons pu juger de la meilleure adéquation de chaque algorithme avec des domaines d’applications ciblés comme, par exemple, l’anonymisation sur Internet, la contribution au développement d’un web sémantique, ou encore une utilisation pour la protection des documents et des donnés numériques. Parallèlement à ces travaux scientifiques fondamentaux, nous avons proposé plusieurs projets de valorisation avec pour objectif la création d’une entreprise de technologies innovantes
Discrete dynamical systems by chaotic or asynchronous iterations have proved to be highly interesting toolsin the field of computer security, thanks to their unpredictible behavior obtained under some conditions. Moreprecisely, these chaotic iterations possess the property of topological chaos and can be programmed in anefficient way. In the state of the art, they have turned out to be really interesting to use notably through digitalwatermarking schemes. However, despite their multiple advantages, these existing algorithms have revealedsome limitations. So, these PhD thesis aims at removing these constraints, proposing new processes whichcan be applied both in the field of digital watermarking and of steganography. We have studied these newschemes on two aspects: the topological security and the security based on a probabilistic approach. Theanalysis of their respective security level has allowed to achieve a comparison with the other existing processessuch as, for example, the spread spectrum. Application tests have also been conducted to steganalyse and toevaluate the robustness of the algorithms studied in this PhD thesis. Thanks to the obtained results, it has beenpossible to determine the best adequation of each processes with targeted application fields as, for example,the anonymity on the Internet, the contribution to the development of the semantic web, or their use for theprotection of digital documents. In parallel to these scientific research works, several valorization perspectiveshave been proposed, aiming at creating a company of innovative technology

碩士
國立交通大學
電信工程系所
92
In this thesis, we address the problem of the performance analysis of audio watermarking systems that use a spread spectrum technique in the discrete cosine transform (DCT) domain. Two tests are involved in the ownership verification process. First, a watermark detector decides whether the audio under test contains a watermark generated with a certain key. If the audio is watermarked , then authorship by the key holder is proved and extraction of hidden message can be performed by a detector. Most current research concentrate on correlation detectors, despite evidence showing that the underlying Gaussian model assumption does not match the intrinsic natures of DCT coefficients. Recognizing this, we first investigate a statistical approach that uses the generalized Gaussian probability to characterize the DCT coefficients and then use it as a basis for the application of statistical decision theory to the design of efficient detector and decoder structures. We also generalize this approach to the possible nonexistence of a statistical description of the original audio.

In spreads pectrum (SS)watermarking of audio signals, since the watermark acts as an additive noise to the host audio signal, the most important challenge is to maintain perceptual transparency. Human perception is a very sensitive apparatus, yet can be exploited to hide some information, reliably. SS watermark embedding has been proposed, in which psycho-acoustically shaped pseudo-random sequences are embedded directly into the time domain audio signal. However, these watermarking schemes use informed detection, in which the original signal is assumed available to the watermark detector. Blind detection of psycho-acoustically shaped SS watermarking is not well addressed in the literature. The problem is still interesting, because, blind detection is more practical for audio signals and, psycho-acoustically shaped watermarks embedding offers the maximum possible watermark energy under requirements of perceptual transparency. In this thesis we study the blind detection of psycho-acoustically shaped SS watermarks in time domain audio signals. We focus on a class of watermark sequences known as random phase watermarks, where the watermark magnitude spectrum is defined by the perceptual criteria and the randomness of the sequence lies in their phase spectrum. Blind watermark detectors, which do not have access to the original host signal, may seem handicapped, because an approximate watermark has to be re-derived from the watermarked signal. Since the comparison of blind detection with fully informed detection is unfair, a hypothetical detection scheme, denoted as semi-blind detection, is used as a reference benchmark. In semi-blind detection, the host signal as such is not available for detection, but it is assumed that sufficient information is available for deriving the exact watermark, which could be embedded in the given signal. Some reduction in performance is anticipated in blind detection over the semi-blind detection. Our experiments revealed that the statistical performance of the blind detector is better than that of the semi-blind detector. We analyze the watermark-to-host correlation (WHC) of random phase watermarks, and the results indicate that WHC is higher when a legitimate watermark is present in the audio signal, which leads to better detection performance. Based on these findings, we attempt to harness this increased correlation in order to further improve the performance. The analysis shows that uniformly distributed phase difference (between the host signal and the watermark) provides maximum advantage. This property is verified through experimentation over a variety of audio signals. In the second part, the correlated nature of audio signals is identified as a potential threat to reliable blind watermark detection, and audio pre-whitening methods are suggested as a possible remedy. A direct deterministic whitening (DDW) scheme is derived, from the frequency domain analysis of the time domain correlation process. Our experimental studies reveal that, the Savitzky-Golay Whitening (SGW), which is otherwise inferior to DDW technique, performs better when the audio signal is predominantly low pass. The novelty of this work lies in exploiting the complementary nature of the two whitening techniques and combining them to obtain a hybrid whitening (HbW) scheme. In the hybrid scheme the DDW and SGW techniques are selectively applied, based on short time spectral characteristics of the audio signal. The hybrid scheme extends the reliability of watermark detection to a wider range of audio signals. We also discuss enhancements to the HbW technique for robustness to temporal offsets and filtering. Robustness of SS watermark blind detection, with hybrid whitening, is determined through a set of experiments and the results are presented. It is seen that the watermarking scheme is robust to common signal processing operations such as additive noise, filtering, lossy compression, etc.

In spreads pectrum (SS)watermarking of audio signals, since the watermark acts as an additive noise to the host audio signal, the most important challenge is to maintain perceptual transparency. Human perception is a very sensitive apparatus, yet can be exploited to hide some information, reliably. SS watermark embedding has been proposed, in which psycho-acoustically shaped pseudo-random sequences are embedded directly into the time domain audio signal. However, these watermarking schemes use informed detection, in which the original signal is assumed available to the watermark detector. Blind detection of psycho-acoustically shaped SS watermarking is not well addressed in the literature. The problem is still interesting, because, blind detection is more practical for audio signals and, psycho-acoustically shaped watermarks embedding offers the maximum possible watermark energy under requirements of perceptual transparency. In this thesis we study the blind detection of psycho-acoustically shaped SS watermarks in time domain audio signals. We focus on a class of watermark sequences known as random phase watermarks, where the watermark magnitude spectrum is defined by the perceptual criteria and the randomness of the sequence lies in their phase spectrum. Blind watermark detectors, which do not have access to the original host signal, may seem handicapped, because an approximate watermark has to be re-derived from the watermarked signal. Since the comparison of blind detection with fully informed detection is unfair, a hypothetical detection scheme, denoted as semi-blind detection, is used as a reference benchmark. In semi-blind detection, the host signal as such is not available for detection, but it is assumed that sufficient information is available for deriving the exact watermark, which could be embedded in the given signal. Some reduction in performance is anticipated in blind detection over the semi-blind detection. Our experiments revealed that the statistical performance of the blind detector is better than that of the semi-blind detector. We analyze the watermark-to-host correlation (WHC) of random phase watermarks, and the results indicate that WHC is higher when a legitimate watermark is present in the audio signal, which leads to better detection performance. Based on these findings, we attempt to harness this increased correlation in order to further improve the performance. The analysis shows that uniformly distributed phase difference (between the host signal and the watermark) provides maximum advantage. This property is verified through experimentation over a variety of audio signals. In the second part, the correlated nature of audio signals is identified as a potential threat to reliable blind watermark detection, and audio pre-whitening methods are suggested as a possible remedy. A direct deterministic whitening (DDW) scheme is derived, from the frequency domain analysis of the time domain correlation process. Our experimental studies reveal that, the Savitzky-Golay Whitening (SGW), which is otherwise inferior to DDW technique, performs better when the audio signal is predominantly low pass. The novelty of this work lies in exploiting the complementary nature of the two whitening techniques and combining them to obtain a hybrid whitening (HbW) scheme. In the hybrid scheme the DDW and SGW techniques are selectively applied, based on short time spectral characteristics of the audio signal. The hybrid scheme extends the reliability of watermark detection to a wider range of audio signals. We also discuss enhancements to the HbW technique for robustness to temporal offsets and filtering. Robustness of SS watermark blind detection, with hybrid whitening, is determined through a set of experiments and the results are presented. It is seen that the watermarking scheme is robust to common signal processing operations such as additive noise, filtering, lossy compression, etc.

碩士
國立中興大學
電機工程學系
90
The advances of computers and communication networks make digital content service such as digital document exchange, E-commerce, video on demand, and digital library very popular. Since digital data can be easily reproduced without any loss, copyright protection becomes an imperative requirement to prevent piracy. Digital watermarking has been proposed as one of the techniques to prevent data piracy and plagiarism. Digital watermarking is a novel and emerging technology. It has developed very quickly for the past few years. A digital watermark is a set of information that is robustly and imperceptibly embedded in the data to be protected. Applications include copyright protection, and authentication. In the thesis, we developed two watermarking techniques using spread-spectrum technique. We interpreted the watermarking technology based on communication theory. The watermark was the signal to be transmitted. The frequency domain of the original image was the transmission channel. The attacks were regarded as channel noise. There were two methods to implement the spread-spectrum system: direct- sequence spread- spectrum (DSSS) and frequency-hopping spread-spectrum (FHSS). Based on these tow methods, we develop FHSS Watermarking and DSSS Watermarking. JPEG compression is the most widely used image because compression technique of its high compression ratio and reasonable image quality. Here, we develop the watermark embedding method especially for JPEG encoding process since block Discrete Cosine Transform (DCT) was used for JPEG. In our approach, a block DCT-based algorithm was used to embed the image watermarking. In order to survive the JPEG compression, the watermark must be embedded in the bands that can with stand the JPEG quantization. Experiments showed that FHSS Watermarking is more resistant to the attack of JPEG compression. The PhotoImpact 5 digital image processing software was used for other attacks. We found that FHSS Watermarking is more robust than DSSS Watermarking in geometric distortions. But in other signal processing modifications, DSSS Watermarking is more robust than FHSS Watermarking. Therefore, we developed a new method that combined with FHSS Watermarking and DSSS Watermarking, we call the new method “combined SS Watermarking”. The experimental results prove that combined SS Watermarking has both the advantages of FHSS Watermarking and DSSS Watermarking. Therefore, combined SS Watermarking is more robust and can with stand many different attacks.

碩士
國立中興大學
電機工程學系
91
The digital watermarks should be hided and invisible by the human visual system. The spread spectrum techniques are used to achieve the goal. The original image is transformed form spatial domain to frequency domain by using discrete wavelet transform (DWT). We insert the spread spectrum PN-code and use modulo-2 operator to secure the watermark. The watermark is embedded into the LL3 sub-band after 3 times DWT. A multilevel detection is proposed to effectively watermark which can increase the retrieval performance. Form the experimental result, the proposed method is robust even under heavy attacks. For example, big compression ratio for JPEG and JPEG 2000, the retrieval watermarks still survive.

碩士
國立臺灣科技大學
電子工程系
91
ABSTRACT Digital watermarking is a technique that aims at hiding a message signal in a multimedia signal (e.g. speech, image, video signal, etc.) for copyright claim, authentication, device control, and broadcast monitoring, etc. In this thesis, we focus on the topic of embedding watermarks into still images. We hope that the embedded watermark induces low impairment to the original image. We also hope that the embedded watermark possesses enough robustness against tampering (intentional or unintentional) su®ered when it is stored or transmitted. We propose to scramble the watermark with pseudo-noise (PN) or orthogonal codes before it is embedded into an image. In terms of the communication scenario, this operation has the e®ect of spectrum spreading, which turns the watermark signal into additive white Gaussian noise (AWGN). In the extraction of the watermark, the aforementioned PN codes are applied once more to the watermarked image, in the meantime spectrum-spreading the original image and thus turning it into AWGN. This original-image-turned AWGN makes some watermark bits been detected incorrectly. In fact, there are some things more that are turned into AWGN, in addition to the original image. The e®ects of tampering operations such as quantization, compression, filtering, or even jamming, are reduced to AWGN as well. It is natural to consider the possibility of incorporating error correction coding (ECC) into the watermarking scheme to facilitate reduction of the watermark bit error rate (BER). We expect that among the various ECC techniques, trellis based schemes (e.g. trellis-coded modulation (TCM) and turbo code) should be adopted. Due to the similarity between the PN/orthogonal coded watermarking and the spread-spectrum communication, it is natural that, following similar derivations regarding data BER in the latter, we derive certain explicit quantitative relationship regarding the trade-o® between the watermark BER and the distortion su®ered by the original image. Finally, we want to point out that the PN codes can be used as keys for secrecy purpose. If we design a scheme to properly set the accessibility of the PN codes to various users of the watermarked images, this thesis may lead to a work that provides the functions of secrecy and authentication, in addition to copyright claim. Keywords : watermark, pseudo-noise code, trellis-coded modulation, turbo code, spread spectrum

碩士
朝陽科技大學
資訊管理系碩士班
93
There have many digital watermarking schemes been explored to solve the problem associated with the copyright enforcement of the multimedia. In this thesis, we present a robust video watermarking technique based on spread spectrum and digital wavelet transformation (DWT) techniques that applied to videos. According to the properties of video, we employ the DWT technique to remove the correlation between spatial domain and temporal domain for dividing a scene of the video into dynamic frames and static ones in the wavelet frequency domain. On the other hand, we develop a watermarking technique using the spread-spectrum technique and complementary modulation strategy. We embed watermarks into all of sub-frequencies throughout. It guarantees that one of the watermarks would survive if the embedded video suffers from attacks. Therefore, the watermark obtains higher robustness. At the same time, we choose some suitable wavelet coefficients to embed watermarks after considering the property of the human visual system. Therefore, the video degradation will not be perceptible. Several experimental results are given to demonstrate the performance of the proposed scheme. The major watermark attacks used in the experiments are grouped into two categories. First category is the common image processings which includes noise addition, sharpening and contrast enhancement upon all frames of the embedded video. The other category is about video processings which includes MPEG compression, frames dropping and averaging. The experimental results show that the proposed scheme has great imperceptibility and is extremely robust against above attacks.

碩士
國立嘉義大學
資訊工程學系研究所
95
The major goal of this study is to embed and detect a watermark for digital video. In general, the spatial watermark embedding technique can not obtain better robustness in comparison with other techniques. This study embeds watermark in spatial domain based on image block which contains features with high intensity, high texture, and high motion, and improves the robustness of the watermark embedded in spatial. Since human visual system (HVS) can’t sense variations caused by high brightness, high texture, and fast motion regions within the video frames, an adaptive watermarking technique was developed to embed watermark signals into these regions. To this end, a digital video is first divided into various frames consisting of several blocks. Each block is then transformed by discrete wavelet transform (DWT). Feature blocks are determined based on the image features discussed above. Spread spectrum incorporated with just notice difference (JND) is performed to embed the watermark into feature blocks or non-feature blocks. Because feature block was designed based on HVS, the watermark is imperceptible to human’s eyes. The embedded watermark can be detected only with a frame. The proposed can resist attacks of linear transformation in digital video frames including frame average, frame reduction, and frame shuttle. Experimental results also demonstrate that the proposed method can obtain better performance in comparison with traditional schemes and resist various malicious attacks for still images such as cropping, JPEG compression, MPEG compression, and etc..

碩士
淡江大學
資訊工程學系碩士在職專班
96
As an effective method for copyright protection and content integrity verification of intellectual property, digital watermarking has become a very active area in the field of multimedia security. We propose a watermarking scheme of H.264 based on Watson’s human visual system. A 4x4 DCT mask combining Watson’s human visual system on DCT will be designed. Using the mask, a spread spectrum watermarking scheme is given to embed the watermark on AC coefficients of 4x4 DCT blocks. And it provides a way to classify 4x4 DCT blocks into edge, textured, or smooth-blocks, and it also is a reference for watermark embedding strength. We also propose a method to resist the frame dropping, reversing, duplicating attacks.

碩士
國立臺灣大學
電機工程學研究所
98
Current portable electronic product requires small in size and high power efficiency for the long-term usage of batteries. The application products include hearing aids, USB speakers, notebooks, wireless speakers, and automotive audio amplifiers. The high power efficiency design can reduce power supply requirements and elimination of heat sinks, and also reduce the size of products. The Class-D amplifier, for its high efficiency, has drawn much attentions recently. A Class-D amplifier with conventional PWM modulation requires an output filter which needs large area and increasing cost. Therefore, we use spread-spectrum modulation scheme to realize a filterless Class-D power amplifier, and reduce output EMI. The negative feedback is applied in this thesis to reduce the harmonic distortion for better linearity. In addition, to avoid the shoot-through current when both power transistors are switched on at the same time, the dead time control is adopted. The circuit is designed using TSMC 0.35μm 2P4M 3.3V CMOS process. The details of the entire circuit will be described thoroughly in this thesis. When a 0.8V, 1KHz input sine wave is applied, the THD is 0.09% and the efficiency is 86%.

博士
國立中興大學
電機工程學系所
98
To embed the multiple watermarks is a way to increase robustness in image watermark. The limitation of embedding multiple watermarks is that the limited capacity of an image severely limits the size of the watermark. Multiple-description coding is a good candidate to solve this limitation by trading off between transmission bandwidth and bit error rate. Traditionally, multiple-description coding is considered in on–off channels where channels are not marred by bit errors but occasional connection outages such as dropped packets. To apply multiple-description coding in image watermarking, we need a form of multiple-description coding for noisy channels instead of on–off channels. In this thesis, we propose to add iterative coding in multiple descriptions in order to combat bit errors in image watermarking. We call this method multiple-description iterative coding (MDIC) image watermarking. We tested our system on six images. On average, bit error did not happen until we compressed the image in JPEG to PSNR 36.97 dB. We concluded that MDIC was a very good way to increase robustness for image watermarking. One of the most popular watermark embedding methods is the direct sequence spread spectrum (DSSS) method. The original DSSS technique divides the image into NxN blocks. These blocks are transformed by discrete cosine transform (DCT). Then, the pseudo-noise (PN) sequences are embedded in selected DCT coefficients within the blocks. In this thesis we explore another two aspects in spread spectrum DCT-based watermarks that are yet unexplored in previous researches. The first aspect is what we called “inter-block” method. In previous DSSS watermark algorithms, the PN sequence from one input bit is embedded in one block. We called this approach “intra-block”. On the other hand, we can embed the PN sequence into several different blocks. Thus, we called it “inter-block” method. The rationale for this “inter-block” approach is that it spreads the same bit into a wider region in the image. This wider spreading may be beneficial in watermark counter-attack. The second aspect is the use of frequency-hop spread spectrum (FHSS). Previous researches indicated that FHSS performed better than DSSS in certain channel condition but FHSS has only been used in audio watermarks. Therefore, applying FHSS watermarks in images is worth investigating. To study the above two aspects, we developed three image watermark algorithms. They are called “intra-block FHSS”, “Inter-block DSSS (IDSSS)” and “Inter-block FHSS (IFHSS)”. These three methods and the original DSSS or “intra-block DSSS” were compared by subjecting them to various watermark attacks. From the experiments, we have the following findings. “Inter-block” techniques perform better against all attacks. For filtering and quantization attacks, IDSSS watermarks performed better. For geometric distortion attacks, IFHSS watermarks performed better. In order to utilize the advantages from these two different approaches, we combined IDSSS and IFHSS into a single watermark system, called Inter-Block Combined (IBC) system, and tested it. The results showed that the IBC can resist a broad range of watermark attacks. Finally, we combined the above two systems, MDIC and IBC, together to construct a whole new architecture, called combined MDIC or CMDIC watermarking system. The experimental results showed that CMDIC can defend a wider scope of watermarking attacks.