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LOW-COMPLEXITY

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LOW-COMPLEXITYLow,low

    LOW-COMPLEXITY

    ,b1.25No.3JOURNALOFELECTRONICS(CHINA)May2008

    LOW.COMPLEXITYREDUNDANCYINSERTIONINMULTIPLE

    DESCRIPTIONCODING

    YangRenerLiJinxiangWenHuafeng

    (CollegeofInformationScienceandEngineering,NingboUniversity,Ningbo315211,China)

    AbstractMultipledescriptioncodinghasrecentlybeenproposedasaiointsourceandchannelcoding

    tosolvetheproblemofrobustimagetransmissionoverunreliablenetwork,anditcanofferavarietyof

    tradeoffbetweensignalredundancyandtransmissionrobustness.Inthisletter.anovelpre

    and

    post

    -processingmethodwithflexibleredundancyinsertionforpolyphasedownsamplingmultiplede-

    scriptioncodingispresented.Theproposedmethodcanbeimplementedaspreandpost

    processingto

    allstandardsforimageandvideocommunications,withobviousadvantages.Simulationresultsshow

    thatthisapproachcanreducethecomputationalcomplexitywhileprovideaflexibleredundancyin

    sertiontomakethesystemrobustforanypacketlosssituationoverdifferentnetworks. KeywordsMultipledescriptionimagecoding;Polyphasedownsampling;Redundancyinsertion

    CLCindexTN919.81

    DOI10.1007/s11767-00702177

I.Introduction

    Videoandimagecommunicationsarebe

    comingmoreandmoreimportantfortheinfra

    structureofglobalinformation.Duetolimited bandwidthandvastamountofmultimediadata, theefficientcompressiontechniquesarerequired. Sourcecodingexploitssometechniquesto

    eliminatetheredundancysoastocompressthe data.Forexample.itexploitstransformcoding andpredictivecodingtoeliminatethespatial andtemperalredundancies.Thereductionof redundancyisalsoaccomplishedbyentropy coding,andirrelevancyisreducedbyvaryingthe quantization.Inaddition,congestionandpacket lossesfrequentlyoccurinthenetworkcommu- nication.However,thecompressedvideostream ismorevulnerabletoerror.especiallywhenex

    ploitingpredictivecodingandentropycoding. Manuscriptreceiveddate:December12,2007;revised date:March1.2008.

    FundedbytheNationalNaturalScienceFoundationof China(No.60671037),NingboIndustryFoundation (No.2007B10051),Zh@angProvinceKeyIndustry Foundation(No.2006C11200),ScientificResearchPundof ZhejiangProvincialEducationDepartmentfNo.20070956. No.20070978,No.20061661),andNingboUniversity FoundationfXK0610031).

    Communicationauthor:YangRener,bornin1968,re- male,Ph.D.,lecturer.CollegeofInformationScienceand Engineing,NingboUniversityjNingbo315211,China.

Emedl:yangrener@nbu.edu.an.

    Sourcecodingandchannelcodinghaveopposite implications.Sourcecodingaimstoreducethe messageredundancyandtoeliminateirrelevancy Incontrast,channelcodingintroducesstructured redundancytocorrecttransmissionerrors.The traditionalapproachtothedesignofcoding algorithmsistoconsideranidealizedmodelfor communicationsystemsthatdividestheproblem domainintotwounrelatedprocesses:source codingandchannelcoding.Recently,Multiple DescriptionCoding(MDC)hasbeenproposedas ajointsourcechannelcoding.Thecodingsystem canproviderobustvideocommunicationover unreliablenetworks,suchastheInternet,when combinedwithpath/servediversityatthecostof reducedcompressionefficiencyl.

    Inthisletter,wepresentanovelpreandpost

    processingmethodwithflexibleredundancyinser

    tionforpolyphasedownsamplingmultiplede

    scriptioncoding.Simulationresultsshowthatthis approachreducescomputationalcomplexitywhile providesaflexibleredundancyinsertiontomake thesystemrobustforanypacketlOSSsituationover differentnetWorks.

    II.MultipleDescriptionCoding(MDC)

    InMDC,asignaliscodedintoanumberof

    separatebitstreams,eachcontainingacomple

    mentarydescriptionofthesigna1.MDCenablesa

usefulreproductionofthesignal,whenanyde

    410QLECTRONICS(CHINA),Vo1.25No.3,May2008 scriptionisreceived.Forthisreason.itisbeneficial toincreasetheprobabilitythatatleastonede

    scriptionisreceivedcorrectlyatanypointintime. MDCprovidesimprovedreconstructedvisualsig

    nalqualityasmoredescriptionsarereceived.Itis proposedbasedonpathdiversitytransmission system,wheredifferentdescriptionsareexplicitly transmittedthroughdifferentnetworkpaths.One canimprovetheeffectivenessofMDCovera packetnetworkbyincreasingthelikelihoodthat thelOSSprobabilitiesforeachdescriptionarein

    dependent.Apathdiversitycommunicationsystem enablestheendto-endapplicationtoeffectivelysee avirtualchannelwithimprovedlOSScharacteristics. Furthermore,theprobabilitythatallofthemul

    tiplepathsaxesimultaneouslycongestedismuch lessthantheprobabilitythatasinglepathis congested.SothispropertymakesMDChighly suitableforpacketnetworkswherenoprioritiza

    tionexistsamongthepackets.

    MDCachievesrobustnessbyintroducingre

    dundancybetweendescriptions.Amultiplede

    scriptioncoderwithtwodescriptionsischaracter

    izedbyfiveparameters:thebitratesofthetwo descriptions,R1andR2,thedistortionDowhen bothdescriptionsarereceived,D1and,the

    distortionwhenonlyonedescriptionjsreceired.

Let=1+denotethetotalbitrate,and

    Do=(D1+D2)/2theaveragedistortionwhenonlya singledescriptionisreceived.Furthermore.1etR' representthereferencebitraterequiredbyasingle descriptioncodertoachievethesamedistortionDo, whenallthebitsarereceivedintactly.There

    dundancyPisdefinedastheadditionalbitrate requiredbythemultipledescriptioncoder,thatis. P=RR.ForafLxedDo(orequivalentlyR),

    theohiectiveofMDCistominimizeD1fora

    givenP.Inliteratures,Doisoftencalledthecentral distortion,andD1thesidedistortion.Varyingthe parameterPinaccordancewithchannelper

    formanceiscrucialforthefinalreconstruction qualityofsource:lessredundancyinsertionineach descriptionisneededforerrorfreetransmissions

    thanforunreliablepackettransfer.

    TheMDCofasourceliesinthegenerationofa numberofequivalentimportancedatastreamsthat. alltogether,carrytheinputinformation.Many methodshavebeenproposedforthegenerationof multipledescriptions.Oneofthefirstpaperswas givenbyVaishampayan-2j.Hisapproachisbasedon amultipledescriptionscalarquantizer,which generatestwosubstreamsbyproducingtwoindi

    cesforeachquantizationleve1.Theindexassign

    mentisdesignedtobeequivalenttoafinequan- tizerwhenbothindicesarereceived.butacoarse quantizerwhenonlyoneindexisreceived.After thismanuscript,othermethodsareproposed.

    Matchingpursuithasbeenusedinafirststageof generatingmultiplebalanceddescriptionsforstill images,inalossynetworkscenario[.

    InRef.[4],the

    authorsproposedtheuseofoversampledfilter

    banksinordertoallowforthereconstructionofthe codedsignalinthepresenceofcoefficientloss. Moreover.theyproposedalowcomplexityMD schemeforimagesbasedonoddandevenrow splittingfortwodescriptiongenerations,whereas thethirddescriptionisobtainedbylowpassfil

    teringeachcolumnandsubsamplingbyafactor2. However,theauthorsstatedthattheobjectivewas nottoproposeacompletecodingschemefora specificapplication.InordertobenefitfromMDC robustnesswhileprovidingrateadaptedcoding, layeredMDChasbeenproposedinRef.51.Such

    approachesdifferintermsofRedundancyRate Distortion(RRD)performanceandcomplexity, someofmultipledescriptioncodingaremore flexiblethanotherinredundancyinsertion.These methodsareconceivedasstandalonecodecs.in

    compatiblewiththestandardssuchasJP2000, H.26X,orthoseoftheMPEGclass.Caramma. ea1.L6jproposedthepolyphasedownsampling multipledescriptioncoding,whichiscompatible withthestandards.However.thedrawbacksofthe PolyphaseDownsamplingMultipleDescription (PDMD)techniquearethelossofcodingefficiency duetotheseparatecodingofeachdescriptionand

    thecertainstiffnessinredundancycontrolamong thedescriptions.Thisconsiderationhasledtothe proposalofMDCschemes.whichcanbeconfigured aspre--andpost--processingstagestobeassociated withanycodecoderstandard.Amongthemethods wementionedabove.thecorrelationamongde. scriptionsisobtainedbymeansof2dimensional

    oversamplingoftheoriginalimage,andbyzero paddingintheDCTtransformdomain.These algorithmsprovideaverysimpledesign,high

YANGeta1.LowcomplexityRedundancyInsertioninMultipleDescriptionCoding411

    codingefficiencyandacapabilityincontrollingthe redundancybetweenthetwodescriptors.These methodshavebeenextendedtovideot7-11],which wellsolvethemismatchproblemsinmultiplede

    scriptionvideocoding[121.

    Themultipledescriptioncodingproposedin Ref.[7],consistsofthreesteps:preprocessing,

    multipledescriptionandpostprocessing.Theaim

    ofthepreprocessingstepismakingthemultiple descriptioncodingflexibleintheredundancyin

    sertion.Toreachthisobjective,thealgorithmDCT transformstheinputsource,padsthetransform domainwithaflexiblenumberofzeros,andthen inverselytransformsthepaddedimage.Ifthe originalimagesizeisD×Dpixelsandthepadding

    parameterisM.thepreprocessedoutputimage

    sizeis(D+M)×(D+M)Thespatialredundancy

    intheoutputimageisproportionaltoM.The

    largertheM.thelargertheredundancyinthe image.Thentheobtainedimageisfedtothe multipledescriptionblockthatsplitsthesource informationintoNequivalentsubsources.Each

    descriptionisthuscodedusingaclassicalimage algorithmandtransmittedoverseparatechannels. Atthereceiverside,allthereceiveddescriptions aredecodedandfedintothepostprocessingblock

    thatprovidestheinverseoperationofpre--proc-- essingstep.

    Themultipledescriptioncodingisbasedon polyphasedownsamplingalgorithm.Thismethodis inspiredbythefollowingidea.Since,inrawimage data,thevalueofanygivenpixelcanbereasonably predictedbythevalueofitsneighbors,thereisa strongcorrelationofinterpixelinformation.By

    exploitingthis,itispossibletocreateamultiple descriptionalgorithmwherethesourceissplitinto Ndescriptionsbyapolyphasedownsampleralong rowsandcolumns.Becauseoftheinterpixelcor

    relationeachgenerateddescriptionmaintainsthe mainfeaturesoftheoriginalimage.Thealgorithm providesaverysimpledesignwithaconsequent computationaltimesaving.

    III.TheProposed

    onPrediction

    Pre-processingBased

    Duetothefactthatthealgorithmsbasedon oversamplingbyzerospaddingtheimageinthe DCTdomainandthenoperatingtheinverse

    transformrequirefurthercomputationalpower, theyareuselessforrealtimeapplication.Inthis letter,weproposeanovelpreprocessingbasedon

    predictionforpolyphasedownsamplingmultiple descriptionwithtwodescriptions,andcomplexity reductioncouldbeobtained.Theaimofthe pre--processingstepistomakethemultiplede-- scriptioncodingflexibleintheredundancyinser

    tion.Toreachthisobjective,whentheimagesource issplitintotwodescriptionsbyapolyphase downsampleralongrowsandcolumns,theextra rowsorcolumnswithflexiblenumberareinserted inbothdescriptions.Inthefollowingpart,forthe sakeofsimplicity,weassumethatthepolyphase downsamplingmultipledescriptionissplitintotwo descriptionsalongrows.Inordertoselectthose extrarowstobeinserted,thedecodingstage,which attemptstopredictthelostrowsfromthereceived ones,issimulatedattheencoderside,andthe predictionerrorofeachrOWestimatedfromits neighboringonesisevaluated.Theextraeven (respectivelyodd)rowsareinsertedintheodd (even).Herewenameitasthepreprocessingbased

    onprediction.

    Theproposedpreprocessingfirstlysplitsthe

    sourceimageofsizeW×H,f0(x,Y)intotwode

    scriptions(,Y)and(,Y)exploitingpolyphase

    downsamplingalongrows(seeFig.1).Thenitpre

    dicts(,Y)as(,Y)using(,Y)byinterpolat

    ing.Theprocessingofobtaining(x,Y)issimilar

    to(,).Finally,wecancalculateabsoluteerror ofeveryrows()and()bycomparing

    (,Y)and(,),(,Y)and(,Y)respectively

    where

    ():?Hl()()

    y=0

    (z):?Hl(,)一五()l

    y=0

    (1)

    (2)

    Then,forallx?[0,w/2],()and()

    aresortedinto()and()respectively.Inthe nextstep,Insert1(N),whichcontainstheinforma- tionofpositionoftheinsertedextrarows,isgained from()and().Insert2(?)isgainedinthe

    similarway,whereNisanumberoftheinserted extrarows.Consequently,onedescripton,forex

    pamle,evendescriptioniscomposedofevenrows

412

    ,

    Q里里!loc?[(INA),Vol,25No.3,May2008 andextraoddrowsdenotedbyInsert1(?).An

    otherdescriptionisproducedbythesamewayas evendescription.Wheneachdescriptioniscom

    Originalimgtge(

    municatedtothedecoder,theinformationofpo

    sitionoftheinsertedextrarowsInsertl(?)isat

    tached.

    Description2

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