VIDEO WATERMARKING IN 3D DCT DOMAIN

Transcription

1 14th Europea Sigal Processig Coferece (EUSIPCO 06), Florece, Italy, September 4-8, 06, copyright by EURASIP VIDEO WATERMARKING IN 3D DCT DOMAIN M. Carli, R. Mazzeo, ad A. Neri AE Departmet Uiversity of Roma TRE, Roma, Italy phoe: + (39) , fax: + (39) , (carli, eri)@uiroma3.it web: ABSTRACT I this work a ovel scheme of embeddig data i a video sequece is preseted. The method is based o a modified Quatizatio Idex Modulatio (QIM) embeddig algorithm i the 3D-DCT domai. Differet zoes i the 3D DCT cube have bee aalyzed i order to obtai better performaces i term of robustess ad imperceptibility. Aalysis of the results shows the effectiveess of the proposed scheme. 1. GENERAL INFORMATION The icreasig presece of multimedia data i every day life is the result of the fusio ad spreadig of several factors as Iteret, third-geeratio mobile commuicatio, WLAN easy to access ad use etworks, ad so o. The availability of low cost systems to process digital data allows a easy maipulatio of them. Despite of the maliciousess or ot of the modificatio or duplicatio of digital data, the availability of digital tools to protect the digital iformatio is eeded. A commoly used method to icrease the security is the watermarkig of digital data. By watermarkig the origial data before its distributio over the etwork, a copyright data, or mark, is embedded i the versio to be distributed so that o other user (malicious or ot) will be able to produce a idetical copy of the origial data ad yet does ot cotai the embedded message. Amog the several costraits to be observed, every embeddig system should ot affect the perceptual quality of the video (ivisibility) producig oticeable distortios i the received data. Besides, the mark should ot be sigificatly altered by malicious (a attempt to alter the mark) or uitetioal (compressio, trasmissio or filterig) operatios (robustess). Furthermore, it should ot be possible to remove the mark from the video, eve if the embeddig scheme is kow (security). These costraits are i some sese atagoist. Icreasig the robustess, for example, geerally icreases the visibility of the mark. Several embeddig methods have bee proposed i the literature; a first classificatio of these methods ca be doe accordig to the particular domai i which the embeddig process is performed. The mark ca be iserted either i the spatial domai [1-3] or i a ad hoc trasform domai such as DCT, Fourier, or wavelet [4-6]. I a previous work [7], the authors proposed a 3D DCT based embeddig system i order to obtai eough capacity to hide the lumiace compoet, dow sampled versio of a frame, 8 bit / pixel, iside a shot of a video. This capacity allows improvig the performaces of a error cocealmet method [9]. The experimetal results have show the effectiveess of the idea ad push us to improve the method to be more robust to wated or uwated data modificatio. I that work [7], three differet embeddig schemes were applied to 3D DCT domai ad the results were ivestigated. I particular, two schemes were obtaied by applyig the 2D modified Cox s embeddig scheme [5], while the third oe cosisted i a hybrid applicatio of Least Sigificat Bit substitutio method to the 3D volume. I this work we employed a differet scheme to select the key frame of a video shot detectio techique ad a differet embeddig scheme i the 3D DCT domai. Furthermore, several schemes have bee studied ad compared to determie the most effective procedure cocerig both visibility ad robustess costraits. The rest of the paper is orgaized as follows. I Sectio 2 the 3D DCT trasform is briefly itroduced. I Sectio 3 the embeddig scheme is preseted, while i Sectio 4 prelimiary results are preseted. Fially, Sectio 5 draws the coclusios. 2. 3D DCT TRANSFORM I literature, 3D trasform based algorithms have bee recetly experimeted, especially for video compressio as they should perform better tha curret block-based motio compesated predictive methods. I particular the 3D DCT has bee proposed for both image [3, 4] ad video compressio. Recetly this domai has also bee cosidered for data embeddig purposes [7]. The 3D Discrete Cosie Trasform (DCT) is a real-valued, separable, orthoormal trasform whose basis fuctios are cosie fuctios. Let X be a 3D sigal of size m by by t, which, i our case, correspods to a set of cosecutive video frames. Let Y be the 3D DCT of X, of size m by by t. The matrix Y ca be computed as follows: N f 1 M 1N 1 k i j tm t= 0 m= 0 = 0 ( 2 + 1) π ( 2 + 1) ( 2t+ 1) π k Ykij = ααα X cos i 2N π icos m i j cos 2M 2N f

2 14th Europea Sigal Processig Coferece (EUSIPCO 06), Florece, Italy, September 4-8, 06, copyright by EURASIP where 1 1, k = 0, i = 0 T M αk = αi = 2 2, else, else T M 1, j = 0 N α j = 2, else N Sice the 3D DCT is a separable fuctio, the above expressio ca be evaluated by applyig the 1D DCT trasform alog each of the three dimesios of X. 3. EMBEDDING ALGORITHM The first step of the proposed system is the partitioig of the video i shots. To this ed, if the ormalized correlatio betwee two cosecutive frames drops below a give threshold, the a shot boudary is detected. Specifically, i the umerical results reported here the threshold has bee set to 0.3, after a set of experimets performed o several videos with differet cotet. The umber of frames icluded i a shot also determies the size of the 3rd dimesio of the 3D sigal support. To be compliat with a previous work, ad to be able to better compare the performace, i the simulatios each shot is composed by 8 frames. The embeddig algorithm is applied every 8 frames cosecutively. I this work we apply the Scalar Costa Scheme embeddig algorithm (SCS)[12, 13] i the 3D-DCT domai. I the followig we breifely summarized the method described i the cited papers. The biary represetatio of the watermark message m is ecoded ito a sequece of watermark letters d. The elemets d belog to a alphabet D = {0,1,..., D 1}. I the followig, let us deote with x the host sigal ad with s the watermarked oe. For a Costa-type embeddig of the watermarks letters d ito the sigal x, a sequeceq = w /α, which is early orthogoal to x, has to be determied. This is reduced to the sample wise operatio d d q = Q x + k x + D k D where k [0,1) is a elemet of cryptographically secured pseudoradom sequece k ad Q { i } deotes a scalar uiform quatizatio process with step size. Fially, the trasmitted watermark sequece is give by: w = αq The watermarked data is give by s= x+ w= x+ αq. At the receiver side, the marked sigal is r = x+ w+ v. I order to extract the mark, the followig rule is applied: y = Q { r k } { r k } For biary SCS ( D = 2), /2 be close to zero if y, where should y d = 0 is trasmitted ad close to ± /2for d = 1. I our experimet we use 1 α =. Some cosideratios ca be carried out about the embeddig scheme. The amout of data to be embedded, the robustess to be achieved, ad especially the purpose of the applicatio are importat factors to be cosidered. The computatioal complexity obviously icreases if the embeddig is performed every 8 frames. O the other side, such a temporal embeddig scheme allows to gai i robustess versus frame droppig, sychroizatio ad trasmissio errors. For istace, whe data hidig is fialized to support error cocealmet [9], the effectiveess of the restoratio is directly related to the quality of the recovered mark. I fact, i that case, the mark cosists i a thumbail of the frame itself: by embeddig more ofte the full gray scale versio of it, the probability to extract a cleaer versio of the mark is higher, resultig i improved visual quality of the processed video. More cosideratios about this problem are i the coclusios. The mark we wat to embed is the best represetative of each shot. The for each shot, a sigle frame summarizig its cotet, amed key frame, is extracted. At this ed, several algorithms, with differet computatioal complexity are available. Here, to face the computatioal burde we resorted to a simple algorithm that selects as key frame the cetral frame of each shot. Sice we are dealig with video, the idea is that the frame i middle will preset the lower iterframe differece from the other frames i the shot. The biary mark sequece is the computed by subsamplig the lumiace compoet of the key frame. Specifically, sequetially scaig the 8 bit plas correspodig to the gray-scale image, we obtai a biary sequece cosistig of 8 biary frames. 4. EXPERIMENTAL RESULTS All the results here reported, refer to the coastguard sequece (144x176 pixels). Tests performed o other sequeces with differet cotet, preset similar performaces. The DCT cube is 144x176x8 elemets ad the embedded mark is a cube of 36x88x8 pixels. The mark has bee iserted i three differet areas of the DCT cube: Startig from coefficiet (,, 1), top left area i the DCT cube. High Zoe. Startig from coefficiet (54, 44, 1), cetral part of the cube. Middle Zoe Startig from coefficiet (8, 88, 1), bottom right area. To test the proposed scheme, we have performed some modificatios of the embeddig parameters. I the first test, we have varied the quatizatio step : by icreasig it, the

3 14th Europea Sigal Processig Coferece (EUSIPCO 06), Florece, Italy, September 4-8, 06, copyright by EURASIP mark robustess ad also the itroduced artifacts icrease. I Figure 1 the average PSNR amog origial ad marked frames is depicted Origial Frames vs Watermarked High Zoe Middle Zoe Delta Figure 1: average PSNR betwee origial ad watermarked frames for the three differet embeddig zoes. As expected, Figure 1 shows that by icreasig the quatizatio factor, the average error of the frame decreases. The maximum differece from the three zoes is below 0.1 db. To measure the perceived quality of the embedded frames, the Weighted-PSNR (WPSNR) [9] fuctio, based o the Cotrast Sesitivity Fuctio, has bee computed. I Figure 2, the results are plotted. It ca be easily oticed that less artifacts are itroduced if the low or the middle areas i the DCT cube are modified. I Figure 3, a example of origial ad marked frame ( =50) is reported. It is useful to metio that, sice we are dealig with a video sequece, small localized artifacts i a sigle frame, are ot to likely visible by a user lookig at the video. W Origial Frames vs Watermarked High Zoe Middle Zoe Delta Figure 2: average W-PSNR betwee origial ad watermarked frames for the three differet embeddig zoes. I the secod trial the robustess versus some attacks has bee tested, i order to select the best embeddig scheme ad to tue some embeddig parameters. Figure 3: origial (left) ad marked frame (right). ( =50) I the followig the mai results obtaied are reported. JPEG compressio of the frames i a shot. The idea is to measure the degradatio of the recovered mark, whe JPEG compressio is performed o the cover sigal. I Figures 4-6 is reported the PSNR of the extracted mark versus the origial oe for compressio rates, 5 quatizatio levels, ad for the three embeddig zoes. It ca be oticed that icreasig the quatizatio level, higher robustess is achieved. I Figure 7, the results of compariso amog the three methods are reported ( =50). As expected, due the JPEG compressio algorithm, the quality of the extracted mark is higher i the High Zoe scheme. A qualitative compariso ca be performed by lookig at Figure 8 i which the origial ad the extracted mark images are reported ( =50,, JPEG quality Factor = ). PSNR 68 db. PSNR attack. This is performed by applyig the classical Stirmark [-11]. I Figure 9 the PSNR curves correspodig to High zoe, are plotted. I this attack, this zoe is more sesitive to the attacks. Nevertheless, the value of the PSNR betwee origial ad extracted mark i the worst case is still over 62 db. I the followig, typical maipulatios of watermarked video have bee cosidered. I all the performed tests, for the quatizatio parameter the value =50 has bee used. Cotrast chage: the DCT coefficiets preset cosiderable variatios especially i the low frequecies. Hece, the High zoe is more sesitive to this attach. I Figure the results correspodig to PSNR vs. Cotrast chage are reported. Note that the value of cotrast chage=±50% correspod to causig the cotet of the frame to be uitelligible. The value of PSNR for the extracted mark is 68 db. Itesity value attack: also i this case the modificatio of itesity values of the video, affects the DCT coefficiets resultig a decreased performaces for the High zoe embeddig scheme. Nevertheless, the PSNR of the extracted mark whe a Middle zoe scheme is adopted, ad a variatio of +% for the itesity is used, is still over db. Video compressio: the watermarked video has bee compressed by usig MPEG1, MPEG2, ad other video coders freely available o Iteret.

4 14th Europea Sigal Processig Coferece (EUSIPCO 06), Florece, Italy, September 4-8, 06, copyright by EURASIP High Zoe - JPEG Delta= Delta= Delta= rates. The mark is almost perfectly recostructed (both MPEG1 ad MPEG2 coders) i High ad Middle Zoe. Little degradatios appear istead i (87,27 db). We obtai comparable results also with the commercial video coders. JPEG High Zoe Middle Zoe 50 Figure 4: JPEG compressio- High Zoe scheme Middle Zoe - JPEG Delta= Delta= Delta= 50 Figure 7: JPEG compressio PSNR compariso at costat quatizatio parameter 50 Figure 5: JPEG compressio- Middle Zoe scheme - JPEG Delta= Delta= Delta= Figure 8: JPEG compressio. Origial ad extracted mark. PSNR=68dB High Zoe - PSNR Delta= Delta= Delta= 50 Figure 6: JPEG compressio- High Zoe scheme 0 50 PSNR Figure 9: PSNR attack- High Zoe scheme I Figure 11 is reported the PSNR betwee origial ad extracted mark correspodig to several compressio rates for a MPEG2 coder. The quality factor 1 idicates a o compressed video. The High Zoe scheme has always better performaces, also at low compressio Frame loss: this situatio ofte occurs durig video trasmissio over packet etworks. We tried to simulate this attack by droppig oe frame startig to the first oe of the 3D DCT block to the last oe, verifyig the effects o the extracted mark. I the detectio phase, i order to rebuilt the sequece of eight frames eeded to compute

5 14th Europea Sigal Processig Coferece (EUSIPCO 06), Florece, Italy, September 4-8, 06, copyright by EURASIP the 3D DCT cube, we simply added as eight frame, the ith oe. The results show the importace of the positio of the mark i the 3D cube. It is also useful to shuffle the data to be embedded to icrease the robustess. Video Maipulatio - Cotrast High Zoe Middle Zoe Cotrast 1 Figure : Cotrast attack Video Compressio High Zoe Middle Zoe Figure 11: Video Compressio attack. High zoe scheme outperforms the other two schemes at high ad middle levels of compressio rates. 5. CONCLUSIONS I this paper, a embeddig scheme, based o Scalar Costa Scheme i 3D DCT domai, for video watermarkig has bee preseted. The performed tests cofirm the effectiveess to use a volume i order to hide a huge amout of data with little or o visible distortio to the host video. The quality of the extracted mark remais high eve after may attacks. The performed simulatios allow selectig the best scheme depedig o applicatio. It is importat to uderlie that digital watermarkig is ot oly data hidig. The requiremets ad the costraits deped o the fial applicatio. The variatios of the embeddig scheme are proposed 50 to uderstad possible real applicatios of the geeral method. I our future study we are goig to apply other watermarkig schemes i 3D domai both for autheticatio ad for cocealmet of the video. REFERENCES [1] N. Nikolaidis ad I. Pitas, Robust image watermarkig i the spatial domai, Sigal Processig, vol. 66, o. 3, pp. 3 3, May [2] R. Wolfgag ad E. Delp, A watermark for digital images, i IEEE Proc. It. Cof. Image Proc. ICIP 1996, 1996, pp [3] D. Gruhl W. Beder ad N. Morimoto, Techiques for data hidig, Tech. rep., MIT Media Lab, Cambridge, MA, [4] M. Bari, F. Bartolii, V. Cappellii, ad A. Piva, A dctdomai system for robust image watermarkig, Sigal Processig, vol. 66, o. 3, pp , May [5] I. Cox, J. Kilia, F. Leighto, ad T. Shamoo, Secure spread spectrum watermarkig for multimedia, IEEE Trasactio o Image Processig, vol. 6, o. 12, December [6] H. Ioue, A. Miyazaki, ad T. Katsura, A image watermarkig method based o the wavelet trasform, i Proceedigs of IEEE Iteratioal Coferece o Image Processig, Kobe, Japa, October 1999, pp [7] M. Carli, C. Adsumilli, V. Razzauti, A. Neri Video watermarkig i 3D DCT domai, Proc. IEEE 05 Iteratioal Workshop o Spectral Methods ad Multirate Sigal Processig, SMMSP 05, Riga, Latvia, Jue -22, 05. [8] S. Pereira, S. Voloshyovskiy, M. Madueño, S. Marchad-Maillet ad T. Pu, Secod geeratio bechmarkig ad applicatio orieted evaluatio, I Iformatio Hidig Workshop III, Pittsburgh, PA, USA, April 01 [9] C.B. Adsumilli, M.C.Q. Farias, S.K. Mitra, ad M. Carli, A robust error cocealmet techique usig data hidig for image ad video trasmissio over lossy chaels, IEEE Trasactios o Circuits ad Systems for Video Techology, vol.15, o 11, Nov. 05 Page(s): [] F. A. P. Petitcolas, R. J. Aderso, M. G. Kuh. Attacks o copyright markig systems, i David Aucsmith (Ed), Iformatio Hidig, Secod Iteratioal Workshop, IH 98, Portlad, Orego, U.S.A., April 15-17, 1998, Proceedigs, LNCS 1525, Spriger-Verlag, ISBN , pp [11] F. A. P. Petitcolas, Watermarkig schemes evaluatio. I.E.E.E. Sigal Processig, vol. 17, o. 5, pp , September 00. [12] J. J. Eggers, R. Bauml, R. Tzschoppe, ad B. Girod, Scalar Costa Scheme for iformatio embeddig, IEEE Trasactios o Sigal Processig, vol. 51, o. 4, pp. 3 19, April 03. [13] M. H. M. Costa, Writig o dirty paper, IEEE Trasactios o Iformatio Theory, vol. 29, o. 3, pp May 1983.