一种稳健的基于小波变换的彩色图像数字水印算法.docx
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一种稳健的基于小波变换的彩色图像数字水印算法
I
ABSTRACT
Therevolutionofthedigitalinformationhasbroughtbigchangesinourlivesandour
society.Thedigitalinformationhasalsogeneratednewchallengesandnewopportunities
forinnovation.Thisthesisdiscussestheissuesregardinginformationhidinginthedigital
imageanditsapplicationforsecurethedigitalmultimedia,addressingboththeoretical
andpracticalaspectsandtackingbothdesignandattackproblems.Inthefundamental
part,wediscussthekeyelementsofwatermarkinganditsapplicationindigitalimage.In
thedesignpart,wepresentnewinformationhidingalgorithmfordigitalcolorimage.The
designprovidesconcreteexamplesregardingthechoiceofembeddingandextraction
mechanisms.Withthegrowthofnetworkedmultimediasystems,theneedofsecure
communicationanddatatransfergoincreasingly.Applicationsarenumerousandvarious
likesatelliteormedicalimagery,orremotemonitoring.Duringimagestransfer,data
integrityisnotreallysecure.Watermarkingcanbeananswertosuchproblems.Inthis
paper,Arobustwavelet-basedcolorimagedigitalwatermarkingschemeisproposed.The
proposeddigitalwatermarkisarandomrealnumberofasequenceofbitsembeddinginto
lowfrequencyofGreencomponentsub-band.Theembeddingmethodisbasedonthree
levelsDiscreteWaveletTransform(DWT)lowcoefficient.Athresholdisusedto
generatefrequencyofwatermarkswiththecompareofcreatedfrequencyofDWTin
embeddingposition.Experimentalresultsshowedthattheembeddedwatermarkisrobust
againstvarioussignalprocessingandcompressionattackssuchasSalt&peppernoise
addition,Cropping,Scaling,JPEGcompression,Meanfiltering,Copyingandpastingand
soon.
Keywords:
Digitalwatermarking,wavelettransform,Colorimage,Greencomponent,
LowfrequencyandRobustness,informationhiding.
3
ListofFigures
Figure2.10.1Schematicdescriptionofsteganography………………………………..5
Figure:
2.2Communicationchannelforcryptosystem…………………………………7
Figure2.3MonogramsfiguringTGERG……………………………………………….8
Figure2.4Genericdigitalwatermarkingscheme………………………………………11
Figure2.5Genericdigitalwatermarkingdecoder……………………………………..11
Figure2.6Genericdigitalwatermarkingscheme………………………………………13
Figure2.7Basicwatermarkembeddingscheme……………………………………….14
Figure2.8BasicwatermarkingDecodingsystem………………………………………15
Figure2.9Classificationofwatermarkingalgorithmsbasedondomainusedforthe
watermarkingembeddingprocess……………………………………………………….16
Figure2.10Classificationofwatermarkingbasedonapplications…………………….17
Figure2.11Digitalwatermarkingrequirementstriangle………………………………20
Figure3.1WatermarksinMarkandDollarbanknotes………………………………...24
Figure3.2Visiblewatermark…………………………………………………………..24
Figure3.3Invisiblewatermark…………………………………………………………25
Figure3.4DeliveringDigitaldatatoatrustedEndsystem……………………...........26
Figure3.5DeliveringDigitaldatatothecustomer……………………………………26
Figure3.6Conflict:
AliceandBobcanbothdetecttheirrespectivewatermarkinimage
I…………………………………………………………………………………………28
Figure3.7ImageLenaCopyingordistributinginprintorelectronicformswithout
writtenpermission………………………………………………………………………31
Figure3.8TheembeddingschemeofthewatermarkingalgorithmasproposedbyCoxet
al.Alotoftheproposedwatermarkingtechniquessharethesamemodel……………..36
Figure3.9Thewaveletpyramidofthree-levelimagedecomposition.Eachlevelconsists
ofthreedetailimages,whichcorrespondtohorizontal,vertical,anddiagonaldetailsof
eachresolutionlevel.xystandsforapplyingfilterxinrowdirectionandfilteryincolumn
direction,whereLmeanslow-passfiltering,Hhigh-passfiltering,andCisthecoarse
image…………………………………………………………………………………….38
4
Figure4.1DWTthreeleveldecompositionflowchatofacolorimage………………...40
Figure4.2WatermarkEmbeddingAlgorithmflowchart………………………………42
Figure4.3WatermarkExtractionAlgorithmflowchart……………………………….44
Figure4.4InvisibilityExperiment(a)OriginalImage(b)WatermarkedImage………...45
Figure4.5WatermarkedImageSufferingvariouskindsofattacks(a,b,c,d).....45
5
ListofTable
Table2.1Numberofpublicationsondigitalwatermarkingduringthepastfewyears
accordingtoWatermarkingworld.org………………………………………………..15
Table2.2Numberofpublicationsondigitalwatermarkingduringthepastfewyears
accordingtoINSPEC,Jan,1999.……………………………………………………….15
Table4.1TheDetectionresponsebetweentheextractedwatermarksandtheattacked
watermarkedimageunderdifferenttypesofattacks……………………………………46
IV
HunanUniversity
StatementofOriginality
Iherebycertifythatthethesissubmittedisbasedontheresearchcarriedoutbymyself
independentlyundertheguidanceandsupervisionofmysupervisor.Anyideasor
quotationsfromtheworkofotherindividualandcollectiveworksarefullyacknowledged
inaccordancewiththestandardreferencingpracticesofthediscipline.
Author'sSignature:
Date:
-May,28,2007
CopyrightStatement
PermissionisherewithgrantedtoHunanUniversitytocirculateandtohavecopiedfor
non-commercialpurposes,atitsdiscretion,thisthesisupontherequestofindividualsor
institutions.Theauthordoesnotreserveotherpublicationrightsandthethesisnormay
extensiveextractsfromitbeprintedorotherwisereproducedwithouttheauthor'swritten
permission.
Thisthesisbelongsto:
1.Secure,andthispowerofattorneyisvalidafter____________.
2.NotSecure
(Pleasemarktheabovecorrespondingcheckbox)
Author'sSignature:
Date:
May,___,2007
Supervisor'sSignature:
Date:
May,___,2007
1
Chapter1Introduction
1.1Preamble
Inrecentyears,thedevelopmentoftheInternetandmultimediatechnology,itiseasierto
produce,distribute,acquireandcopydigitalmediaproductssuchasdigitaltext,image,
videoandaudio[1].Thatiswhy,itisnecessarytoprotectthedigitalproduction.The
digitalwatermarkingtechniquecansolvetheproblem.Thedigitalwatermarkwhichis
representstheownershipoftheowneraccordingtotheembeddinginformationintothe
originalimage.Itcanbeappliedtodifferentapplicationsincludingdigitalsignatures,
fingerprinting,broadcastandpublicationmonitoring,authentication,copycontroland
secretcommunication[2].Usually,aneffectivedigitalwatermarkschemeprovidesthe
threemajorproperties[3].(i)Imperceptibility(ii)Robustnessand(iii)Unambiguity.The
embeddedwatermarkingmustbeimperceptibilityandinvisiblebecauseoftwoprimary
concerns;firstlyweshouldnotlowerthequalityoftheoriginalimageoritwillthebreak
theaestheticfeelinganddiminishthecommercialvalueoftheoriginal.Second,ifthe
watermarkembeddedisdetectedbyhacker,itwillbeeasilybrokeorberemoved.
Watermarkedimageshouldberobust.Thewatermarkcouldstillbeextractedclearlyafter
somedigitalimageprocessingsuchaslossyorlosslessimagecompression.Inthe
watermarkextractionprocess,itshouldbeunambiguoustoprovetheownershipofthe
owner[3].Oneoftheprimarywatermarkingdesigningconsiderationsisthatthe
invisibilityandrobustnessoftencollide[4].Inordertoimprovetherobustnessofthe
watermarkingscheme,wemustembedmoreandmorewatermarkinformationand
thereforecausethequalityoftheimagelowerandlower.Itseemslikethattheoriginal
imagehasbeeninterferedwithmuchmorenoise.Ontheotherhand,inordertokeepthe
qualityoftheoriginalimage,weembedfewerinformationandhighrobustof
watermarkingscheme.Usually,therearetwokindsofbasicwatermarkingdesignscheme
[4][5],
(1)Spatialdomainand
(2)TransformdomainorFrequencydomain(DCT,DWT,
DFT).Thewatermarkismorerobustinthefrequencydomainthaninthespatialdomain.
Sothemethodwechoosefrequencydomaintoembedthewatermark.Therearemany
2
researchesanddevelopshavebeendonegrayscaleimagebutthecolorimageisnot
sufficient.Nowadaycolorimageisdominantmostofthepartsofapplications.
EmbeddinginformationincolorimageRGBcolorchannelishighlycorrelatedsoitisnot
suitableforembeddingwatermark.Someproposedembeddingschemesfocuson
embeddingwatermarksintheYcomponent(luminance)inYIQmodel.Kutteretal[6]
embedthewatermarkbymodifyingselectedsetpixelsinthebluechannelbecauseofits
lowsensitivitytohumanperception.ThebluechannelisthebestchoosetoJPEG
compressionamongtheRGBbecauseofitslowsensitivitytohumanperception.Sothe
hiddenwatermarkiseasytobelost.RedChannelembeddingwatermarkproblemisits
verylargeenergyloss.DuringtheRGBtruecolorimagecompressedintoJEPG,the
embeddingwatermarkintheredchanneliseasytolostanddifficulttoextract.Otherwise
greenchannelcanendureJEPGcompressionandtheembeddedwatermarkisrobust
enough.SoourselectisGreenchanneltoembedwatermarkinformationtoexamineit’s
capability.
1.2Motivation
Modernageistheageofdigitaltechnologies.Thedigitalinformationexchangelikeas
Internetandmultimediatechnologybecomeseasiertoproduce,distribute,modify,
acquireandcopydigitalmediaproductssuchasdigitaltext,image,videoandaudio.But
theseresultscreateseriousproblembecauseunauthorizedcopyingandmodificationof
thecontext.Anyonecaneasilycopythedigitalproductsfrominternetanditbecomes
veryeasytogetbenefitfromitwithoutownerpermission.Eventheycanclaimthatthey
aretheownersofthecopyright.
Forthisreasonpiracybecomesgreatthreatforinnovationandbusiness.Inordertosolve
intellectualpropertyproblemsofthedigitalage,theownerhavetheprotecti