外文翻译数字图像处理方法的研究.docx

外文翻译数字图像处理方法的研究.docx

《外文翻译数字图像处理方法的研究.docx》由会员分享，可在线阅读，更多相关《外文翻译数字图像处理方法的研究.docx（14页珍藏版）》请在冰点文库上搜索。

外文翻译数字图像处理方法的研究

Theresearchofdigitalimageprocessingtechnique

1Introduction

Interestindigitalimageprocessingmethodsstemsfromtwoprincipalapplicationareas:

improvementofpictorialinformationforhumaninterpretation;andprocessingofimagedataforstorage,transmission,andrepresentationforautonomousmachineperception.Thischapterhasseveralobjectives:

（1）todefinethescopeofthefieldthatwecallimageprocessing;

（2）togiveahistoricalperspectiveoftheoriginsofthisfield;（3）togiveanideaofthestateoftheartinimageprocessingbyexaminingsomeoftheprincipalareainwhichitisapplied;（4）todiscussbrieflytheprincipalapproachesusedindigitalimageprocessing;（5）togiveanoverviewofthecomponentscontainedinatypical,general-purposeimageprocessingsystem;and（6）toprovidedirectiontothebooksandotherliteraturewhereimageprocessingworknormallyisreporter.

1.1WhatIsDigitalImageProcessing?

Animagemaybedefinedasatwo-dimensionalfunction,f（x,y）,wherexandyarespatial（plane）coordinates,andtheamplitudeoffatanypairofcoordinates（x,y）iscalledtheintensityorgrayleveloftheimageatthatpoint.Whenx,y,anddigitalimage.Thefieldofdigitalimageprocessingreferstoprocessingdigitalimagesbymeansofadigitalcomputer.Notethatadigitalimageiscomposedofafinitenumberofelements,eachofwhichhasaparticularlocationandvalue.Theseelementsarereferredtoaspictureelements,imageelements,pels,andpixels.Pixelisthetermmostwidelyusedtodenotetheelementsofadigitalimage.WeconsiderthesedefinitionsinmoreformaltermsinChapter2.

Visionisthemostadvancedofoursenses,soitisnotsurprisingthatimagesplaythesinglemostimportantroleinhumanperception.However,unlikehumanwhoarelimitedtothevisualbandoftheelectromagnetic（EM）spectrum,imagingmachinescoveralmosttheentireEMspectrum,rangingfromgammatoradiowaves.Theycanoperateonimagesgeneratedbysourcesthathumanarenotaccustomedtoassociatingwithimage.Theseincludeultrasound,electronmicroscopy,andcomputer-generatedimages.Thus,digitalimageprocessingencompassesawideandvariedfieldofapplication.

Thereisnogeneralagreementamongauthorsregardingwhereimageprocessingstopsandotherrelatedareas,suchasimageanalysisandcomputervision,start.Sometimesadistinctionismadebydefiningimageprocessingasadisciplineinwhichboththeinputandoutputofaprocessareimages.Webelievethistobealimitingandsomewhatartificialboundary.Forexample,underthisdefinition,eventhetrivialtaskofcomputingtheaverageintensityofanimage（whichyieldsasinglenumber）wouldnotbeconsideredanimageprocessingoperation.Ontheotherhand,therearefieldssuchascomputervisionwhoseultimategoalistousecomputertoemulatehumanvision,includinglearningandbeingabletomakeinferencesandtakeactionsbasedonvisualinputs.Thisareaitselfisabranchofartificialintelligence（AI）whoseobjectiveistoemulatehumanintelligence.ThisfieldofAIisinitsearlieststagesofinfancyintermsofdevelopment,withprogresshavingbeenmuchslowerthanoriginallyanticipated.Theareaofimageanalysis（alsocalledimageunderstanding）isinbetweenimageprocessingandcomputervision.

Therearenoclear-cutboundariesinthecontinuumfromimageprocessingatoneendtocomputervisionattheother.However,oneusefulparadigmistoconsiderthreetypesofcomputerizedprocessesisthiscontinuum:

low-,mid-,andhigh-everprocesses.Low-levelprocessesinvolveprimitiveoperationsuchasimagepreprocessingtoreducenoise,contrastenhancement,andimagesharpening.Alow-levelprocessischaracterizedbythefactthatbothitsinputandoutputareimages.Mid-levelprocessingonimagesinvolvestaskssuchassegmentation（partitioninganimageintoregionsorobjects）,descriptionofthoseobjectstoreducethemtoaformsuitableforcomputerprocessing,andclassification（recognition）ofindividualobject.Amid-levelprocessischaracterizedbythefactthatitsinputsgenerallyareimages,butitsoutputisattributesextractedfromthoseimages（e.g.,edgescontours,andtheidentityofindividualobject）.Finally,higher-levelprocessinginvolves“makingsense”ofanensembleofrecognizedobjects,asinimageanalysis,and,atthefarendofthecontinuum,performingthecognitivefunctionnormallyassociatedwithvision.

Basedontheprecedingcomments,weseethatalogicalplaceofoverlapbetweenimageprocessingandimageanalysisistheareaofrecognitionofindividualregionsorobjectsinanimage.Thus,whatwecallinthisbookdigitalimageprocessingencompassesprocesseswhoseinputsandoutputsareimagesand,inaddition,encompassesprocessesthatextractattributesfromimages,uptoandincludingtherecognitionofindividualobjects.Asasimpleillustrationtoclarifytheseconcepts,considertheareaofautomatedanalysisoftext.Theprocessesofacquiringanimageoftheareacontainingthetext.Preprocessingthatimages,extracting（segmenting）theindividualcharacters,describingthecharactersinaformsuitableforcomputerprocessing,andrecognizingthoseindividualcharactersareinthescopeofwhatwecalldigitalimageprocessinginthisbook.Makingsenseofthecontentofthepagemaybeviewedasbeinginthedomainofimageanalysisandevencomputervision,dependingonthelevelofcomplexityimpliedbythestatement“makingcense.”Aswillbecomeevidentshortly,digitalimageprocessing,aswehavedefinedit,isusedsuccessfullyinabroadrangofareasofexceptionalsocialandeconomicvalue.Theconceptsdevelopedinthefollowingchaptersarethefoundationforthemethodsusedinthoseapplicationareas.

1.2TheOriginsofDigitalImageProcessing

Oneofthefirstapplicationsofdigitalimageswasinthenewspaperindustry,whenpictureswerefirstsentbysubmarinecablebetweenLondonandNewYork.IntroductionoftheBartlanecablepicturetransmissionsystemintheearly1920sreducedthetimerequiredtotransportapictureacrosstheAtlanticfrommorethanaweektolessthanthreehours.Specializedprintingequipmentcodedpicturesforcabletransmissionandthenreconstructedthematthereceivingend.Figure1.1wastransmittedinthiswayandreproducedonatelegraphprinterfittedwithtypefacessimulatingahalftonepattern.

Someoftheinitialproblemsinimprovingthevisualqualityoftheseearlydigitalpictureswererelatedtotheselectionofprintingproceduresandthedistributionofintensitylevels.TheprintingmethodusedtoobtainFig.1.1wasabandonedtowardtheendof1921infavorofatechniquebasedonphotographicreproductionmadefromtapesperforatedatthetelegraphreceivingterminal.Figure1.2showsanimagesobtainedusingthismethod.TheimprovementsoverFig.1.1areevident,bothintonalqualityandinresolution.

FIGURE1.1AdigitalpictureproducedinFIGURE1.2Adigitalpicture

1921fromacodedtapebyatelegraphprintermadein1922fromatapepunched

Withspecialtypefaces（McFarlane）afterthesignalshadcrossedthe

Atlantictwice.Someerrorsare

Visible.（McFarlane）

TheearlyBartlanesystemswerecapableofcodingimagesinfivedistinctlevelofgray.Thiscapabilitywasincreasedto15levelsin1929.Figure1.3istypicaloftheimagesthatcouldbeobtainedusingthe15-toneequipment.Duringthisperiod,introductionofasystemfordevelopingafilmplatevialightbeamsthatweremodulatedbythecodedpicturetapeimprovedthereproductionprocessconsiderably.

Althoughtheexamplesjustcitedinvolvedigitalimages,theyarenotconsidereddigitalimageprocessingresultsinthecontextofourdefinitionbecausecomputerwerenotinvolvedintheircreation.Thus,thehistoryofdigitalprocessingisintimatelytiedtothedevelopmentofthedigitalcomputer.Infactdigitalimagesrequiresomuchstorageandcomputationalpowerthatprogressinthefieldofdigitalimageprocessinghasbeendependentonthedevelopmentofdigitalcomputersofsupportingtechnologiesthatincludedatastorage,display,andtransmission.

TheideaofacomputergoesbacktotheinventionoftheabacusinAsiaMinor,morethan5000yearsago.Morerecently,thereweredevelopmentsinthepasttwocenturiesthatarethefoundationofwhatwecallcomputertoday.However,thebasisforwhatwecallamoderndigitalcomputerdatesbacktoonlythe1940swiththeintroductionbyJohnvonNeumannoftwokeyconcepts:

（1）amemorytoholdastoredprogramanddata,and

（2）conditionalbranching.Theretwoideasarethefoundationofacentralprocessingunit（CPU）,whichisattheheartofcomputertoday.StartingwithvonNeumann,therewereaseriesofadvancesthatledtocomputerspowerfulenoughtobeusedfordigitalimageprocessing.Briefly,theseadvancesmaybesummarizedasfollow:

（1）theinventionofthetransistorbyBellLaboratoriesin1948;

（2）thedevelopmentinthe1950sand1960softhehigh-levelprogramminglanguagesCOBOL（CommonBusiness-OrientedLanguage）andFORTRAN（FormulaTranslator）;

（3）theinventionoftheintegratedcircuit（IC）atTexasInstrumentsin1958;

（4）thedevelopmentofoperatingsystemintheearly1960s;

（5）thedevelopmentofthemicroprocessor（asinglechipconsistingofthecentralprocessingunit,memory,andinputandoutputcontrols）byInterintheearly1970s;

（6）introductionbyIBMofthepersonalcomputerin1981;

（7）progressiveminiaturizationofcomponents,startingwithlargescaleintegration（LI）inthelate1970s,thenverylargescaleintegration（VLSI）inthe1980s,tothepresentuseofultralargescaleintegr