多媒体技术原理 视频中的基本概念课件

Chapter5

FundamentalConceptsinVideo5.1 TypesofVideoSignals5.2 AnalogVideo5.3 DigitalVideo5.4 FurtherExplorationChapter5

FundamentalConcepts15.1 TypesofVideoSignalsComponentvideo（分量视频）Compositevideo（复合视频）S-Video（超视频）5.1 TypesofVideoSignalsCom25.1 TypesofVideoSignalsComponentvideoHigher-endvideosystemsmakeuseofthreeseparatevideosignalsforthered,green,andblueimageplanesEachcolorchannelissentasaseparatevideosignal.MostcomputersystemsuseComponentVideo,withseparatesignalsforR,G,andBsignals.Foranycolorseparationscheme,ComponentVideogivesthebestcolorreproductionsincethereisno“crosstalk”betweenthethreechannels.ThisisnotthecaseforS-VideoorCompositeVideo,discussednext.Componentvideo,however,requiresmorebandwidthandgoodsynchronizationofthethreecomponents.5.1 TypesofVideoSignalsCom35.1 TypesofVideoSignalsComponentvideo5.1 TypesofVideoSignalsCom4CompositeVideo—OneSignalCompositevideo

color(“chrominance”)andintensity(“luminance”)signalsaremixedintoasinglecarrierwave.Chrominanceisacompositionoftwocolorcomponents(IandQ,orUandV).InNTSCTV,e.g.,IandQarecombinedintoachromasignal,andacolorsubcarrieristhenemployedtoputthechromasignalatthehigh-frequencyendofthesignalsharedwiththeluminancesignal.Thechrominanceandluminancecomponentscanbeseparatedatthereceiverendandthenthetwocolorcomponentscanbefurtherrecovered.CompositeVideo—OneSignalCo5CompositeVideo—OneSignalCompositevideoWhenconnectingtoTVsorVCRs,CompositeVideousesonlyonewireandvideocolorsignalsaremixed,notsentseparately.Theaudioandsyncsignalsareadditionstothisonesignal.Sincecolorandintensityarewrappedintothesamesignal,someinterferencebetweentheluminanceandchrominancesignalsisinevitable.CompositeVideo—OneSignalCo6CompositeVideo—OneSignalCompositevideoCompositeVideo—OneSignalCo7S-Video—TwoSignalsS-Videoasacompromise,(separatedvideo,orSuper-video,e.g.,inS-VHS)usestwowires,oneforluminanceandanotherforacompositechrominancesignal.Asaresult,thereislesscrosstalkbetweenthecolorinformationandthecrucialgray-scaleinformation.S-Video—TwoSignalsS-Video8S-Video—TwoSignalsS-VideoThereasonforplacingluminanceintoitsownpartofthesignalisthatblack-and-whiteinformationismostcrucialforvisualperception.Infact,humansareabletodifferentiatespatialresolutioningrayscaleimageswithamuchhigheracuitythanforthecolorpartofcolorimages.Asaresult,wecansendlessaccuratecolorinformationthanmustbesentforintensityinformation—wecanonlyseefairlylargeblobsofcolor,soitmakessensetosendlesscolordetail.S-Video—TwoSignalsS-Video9S-Video—TwoSignalsS-Videosmallroundconnectorwithtwoseparatevideosignals,onecarryingbrightness(luminance),theothercarryingcolor(chroma).AlsoreferredtoasY/CvideoS-Video—TwoSignalsS-Video10电视扫描和同步扫描分类非隔行扫描（逐行扫描）(progressivescanning)计算机显示器隔行扫描(interlacedscanning)电视电视扫描和同步扫描分类115.2 AnalogVideoInTV,andinsomemonitorsandmultimediastandardsaswell,anothersystem,called“interlaced”scanningisused:Theodd-numberedlinesaretracedfirst,andthentheeven-numberedlinesaretraced.Thisresultsin“odd”and“even”fields—twofieldsmakeuponeframe.Infact,theoddlines(startingfrom1)endupatthemiddleofalineattheendoftheoddfield,andtheevenscanstartsatahalf-waypoint.5.2 AnalogVideoInTV,andin125.2 AnalogVideoFigure5.1showstheschemeused.Firstthesolid(odd)linesaretraced,PtoQ,thenRtoS,etc.,endingatT;thentheevenfieldstartsatUandendsatV.ThejumpfromQtoR,etc.inFigure5.1iscalledthehorizontalretrace,duringwhichtheelectronicbeamintheCRTisblanked.ThejumpfromTtoUorVtoPiscalledtheverticalretrace.Fig.5.1:Interlacedrasterscan5.2 AnalogVideoFigure5.1sh135.2 AnalogVideo5.2 AnalogVideo145.2 AnalogVideoBecauseofinterlacing,theoddandevenlinesaredisplacedintimefromeachother—generallynotnoticeableexceptwhenveryfastactionistakingplaceonscreen,whenblurringmayoccur.Forexample,inthevideoinFig.5.2,themovinghelicopterisblurredmorethanisthestillbackground.5.2 AnalogVideoBecauseofin155.2 AnalogVideoFig.5.2:Interlacedscanproducestwofieldsforeachframe.(a)Thevideoframe,(b)Field1,(c)Field2,(d)DifferenceofFields(a)(b)(c)(d)5.2 AnalogVideoFig.5.2:Int165.2 AnalogVideoSinceitissometimesnecessarytochangetheframerate,resize,orevenproducestillsfromaninterlacedsourcevideo,variousschemesareusedto“de-interlace”it.Thesimplestde-interlacingmethodconsistsofdiscardingonefieldandduplicatingthescanlinesoftheotherfield.Theinformationinonefieldislostcompletelyusingthissimpletechnique.Othermorecomplicatedmethodsthatretaininformationfrombothfieldsarealsopossible.5.2 AnalogVideoSinceitiss17TVStandardsNTSC美国、加拿大等大部分西半球国家，以及日本、韩国、菲律宾PAL德国、英国等一些西欧国家，及中国、朝鲜等国家SECAM法国、及东欧国家TVStandardsNTSC18WorldTVStandards

NTSCPALSECAMPAL/SECAMUnknownWorldTVStandards

NTSCPALSECA19NTSCVideoNTSC(NationalTelevisionSystemCommittee)TVstandardusesthefamiliar4:3aspectratio(i.e.,theratioofpicturewidthtoitsheight)anduses525scanlinesperframeat30framespersecond(fps).ItismostlyusedinNorthAmericaandJapan.NTSCVideoNTSC(NationalTelev20NTSCVideoFeaturesofNTSCNTSCfollowstheinterlacedscanningsystem,andeachframeisdividedintotwofields,with262.5lines/field.Thusthehorizontalsweepfrequencyis525×29.97≈15,734lines/sec,sothateachlineissweptoutin1/15.734×103sec≈63.6μsec.Sincethehorizontalretracetakes10.9μsec,thisleaves52.7μsecfortheactivelinesignalduringwhichimagedataisdisplayed(seeFig.5.3).NTSCVideoFeaturesofNTSC21NTSCVideoFig.5.4showstheeffectof“verticalretrace&sync”and“horizontalretrace&sync”ontheNTSCvideoraster.Fig.5.4:Videoraster,includingretraceandsyncdataNTSCVideoFig.5.4showsthee22NTSCVideoVerticalretracetakesplaceduring20linesreservedforcontrolinformationatthebeginningofeachfield.Hence,thenumberofactivevideolinesperframeisonly485.Similarly,almost1/6oftherasterattheleftsideisblankedforhorizontalretraceandsync.Thenon-blankingpixelsarecalledactivepixels.Sincethehorizontalretracetakes10.9μsec,thisleaves52.7μsecfortheactivelinesignalduringwhichimagedataisdisplayed(seeFig.5.3).Itisknownthatpixelsoftenfallin-betweenthescanlines.Therefore,evenwithnon-interlacedscan,NTSCTVisonlycapableofshowingabout340(visuallydistinct)lines,i.e.,about70%ofthe485specifiedactivelines.Withinterlacedscan,thiscouldbeaslowas50%.NTSCVideoVerticalretracetak23NTSCVideoNTSCvideoisananalogsignalwithnofixedhorizontalresolution.Thereforeonemustdecidehowmanytimestosamplethesignalfordisplay:eachsamplecorrespondstoonepixeloutput.A“pixelclock”isusedtodivideeachhorizontallineofvideointosamples.Thehigherthefrequencyofthepixelclock,themoresamplesperlinethereare.Differentvideoformatsprovidedifferentnumbersofsamplesperline,aslistedintheTable5.1.FormatSamplesperlineVHS240S-VHS400-425Betamax500Standard8m300Hi-8mm425Table5.1:SamplesperlineforvariousvideoformatsNTSCVideoNTSCvideoisanana24ColorModelandModulationofNTSCNTSCusestheYIQcolormodel,andthetechniqueofquadrature

modulationisemployedtocombine(thespectrallyoverlappedpartof)I(in-phase)andQ(quadrature)signalsintoasinglechromasignalC:C=Icos(Fsct)+Qsin(Fsct) (5.1)Thismodulatedchromasignalisalsoknownasthecolorsubcarrier,whosemagnitudeis ,andphaseistan−1(Q/I).ThefrequencyofCisFsc≈3.58MHz.TheNTSCcompositesignalisafurthercompositionoftheluminancesignalYandthechromasignalasdefinedbelow:composite=Y+C=Y+Icos(Fsct)+Qsin(Fsct) (5.2)ColorModelandModulationof25ColorModelandModulationofNTSCFig.5.5:NTSCassignsabandwidthof4.2MHztoY,andonly1.6MHztoIand0.6MHztoQduetohumaninsensitivitytocolordetails(highfrequencycolorchanges).

Fig.5.5:InterleavingYandCsignalsintheNTSCspectrum.ColorModelandModulationof26DecodingNTSCSignalsThefirststepindecodingthecompositesignalatthereceiversideistheseparationofYandC.AftertheseparationofYusingalow-passfilter,thechromasignalCcanbedemodulatedtoextractthecomponentsIandQseparately.ToextractI:MultiplythesignalCby2cos(Fsct),i.e.,DecodingNTSCSignalsThefirst27DecodingNTSCSignalsApplyalow-passfiltertoobtainIanddiscardthetwohigherfrequency(2Fsc)terms.Similarly,QcanbeextractedbyfirstmultiplyingCby2sin(Fsct)andthenlow-passfiltering.DecodingNTSCSignalsApplyal28DecodingNTSCSignalsTheNTSCbandwidthof6MHzistight.Itsaudiosubcarrierfrequencyis4.5MHz.ThePicturecarrierisat1.25MHzwhichplacesthecenteroftheaudiobandat1.25+4.5=5.75MHzinthechannel(Fig.5.5).Butnoticethatthecolorisplacedat1.25+3.58=4.83MHz.Sotheaudioisabittooclosetothecolorsubcarrieritwasacauseforpotentialinterferencebetweentheaudioandcolorsignals.ItwaslargelyduetothisreasonthattheNTSCcolorTVactuallysloweddownitsframerateto30×1,000/1,001≈29.97fps.Asaresult,theadoptedNTSCcolorsubcarrierfrequencyisslightlyloweredtofsc=30×1,000/1,001×525×227.5≈3.579545MHz,where227.5isthenumberofcolorsamplesperscanlineinNTSCbroadcastTV.DecodingNTSCSignalsTheNTSC29PALVideoPAL(PhaseAlternatingLine)uses625scanlinesperframe,at25frames/second,witha4:3aspectratioandinterlacedfields.PALusestheYUVcolormodel.Itusesan8MHzchannelandallocatesabandwidthof5.5MHztoY,and1.8MHzeachtoUandV.Thecolorsubcarrierfrequencyisfsc≈4.43MHz.Inordertoimprovepicturequality,chromasignalshavealternatesigns(e.g.,+Uand-U)insuccessivescanlines,hencethename“PhaseAlternatingLine”.Thisfacilitatestheuseofa(linerate)combfilteratthereceiverthesignalsinconsecutivelinesareaveragedsoastocancelthechromasignals(thatalwayscarryoppositesigns)forseparatingYandCandobtaininghighqualityYsignals.PALiswidelyusedinWesternEurope,China,India,andmanyotherpartsoftheworld.PALVideoPAL(PhaseAlternatin30SECAMVideoSECAMstandsforSystèmeElectroniqueCouleurAvecMémoirethethirdmajorbroadcastTVstandard.SECAMalsouses625scanlinesperframe,at25framespersecond,witha4:3aspectratioandinterlacedfields.SECAMandPALareverysimilar.Theydifferslightlyintheircolorcodingscheme:InSECAM,UandVsignalsaremodulatedusingseparatecolorsubcarriersat4.25MHzand4.41MHzrespectively.Theyaresentinalternatelines,i.e.,onlyoneoftheUorVsignalswillbesentoneachscanline.SECAMVideoSECAMstandsforSy31ComparisonofthemajorTVStandardsTable5.2:ComparisonofAnalogBroadcastTVSystemsTVSystemFrameRate(fps)No.ofScanLinesTotalChannelWidth(MHz)BandwidthAllocation(MHz)YIorUQorVNTSC29.975256.0PAL256258.0SECAM256258.06.02.02.0ComparisonofthemajorTVSta325.3 DigitalVideoTheadvantagesofdigitalrepresentationforvideoVideocanbestoredondigitaldevicesorinmemory,readytobeprocessed(noiseremoval,cutandpaste,etc.),andintegratedtovariousmultimediaapplications;Directaccessispossible,whichmakesnonlinearvideoeditingachievableasasimple,ratherthanacomplex,task;Repeatedrecordingdoesnotdegradeimagequality;Easeofencryptionandbettertolerancetochannelnoise.5.3 DigitalVideoTheadvantag33ChromaSubsamplingSincehumansseecolorwithmuchlessspatialresolutionthantheyseeblackandwhite,itmakessenseto“decimate”thechrominancesignal.Interesting(butnotnecessarilyinformative!)nameshavearisentolabelthedifferentschemesused.ChromaSubsamplingSincehumans34ChromaSubsamplingSubsampling对亮度信号和色差信号采用相同的采样频率进行采样对亮度信号和色差信号采用不同的采样频率进行采样图像子采样的概念对色差信号使用的采样频率比对亮度信号使用的采样频率低的采样方法ChromaSubsamplingSubsampling35ChromaSubsamplingSubsampling在数字图像压缩技术中得到广泛应用最简便的图像压缩技术恐怕就要算图像子采样。基本依据是人的视觉系统所具有的两个特性人眼对色度信号的敏感程度比对亮度信号的敏感程度低，利用这个特性可把颜色信号去掉一些而使人不易察觉人眼对图像细节的分辨能力有一定的限度，利用这个特性可把图像中的高频信号去掉而使人不易察觉ChromaSubsamplingSubsampling36ChromaSubsamplingSubsampling4:4:4这种采样格式不是子采样格式，它是指在每条扫描线上每4个连续的采样点取4个亮度Y样本、4个红色差Cr样本和4个蓝色差Cb样本，每个像素用3个样本表示4:2:2在每条扫描线上，每4个连续的采样点取4个亮度Y样本、2个红色差Cr样本和2个蓝色差Cb样本，平均每个像素用2个样本表示4:1:1在每条扫描线上，每4个连续的采样点取4个亮度Y样本、1个红色差Cr样本和1个蓝色差Cb样本，平均每个像素用1.5个样本表示4:2:0在水平和垂直方向上，每2个连续采样点上取2个亮度Y样本、1个红色差Cr样本和1个蓝色差Cb样本，每个像素用1.5个样本表示ChromaSubsamplingSubsampling37ChromaSubsamplingTobeginwith,numbersaregivenstatinghowmanypixelvalues,perfouroriginalpixels,areactuallysent:Thechromasubsamplingscheme“4:4:4”indicatesthatnochromasubsamplingisused eachpixel’sY,CbandCrvaluesaretransmitted,4foreachofY,Cb,Cr.Thescheme“4:2:2”indicateshorizontalsubsamplingoftheCb,Crsignalsbyafactorof2. offourpixelshorizontallylabelledas0to3,allfourYsaresent,andeverytwoCb’sandtwoCr’saresent,as(Cb0,Y0)(Cr0,Y1)(Cb2,Y2)(Cr2,Y3)(Cb4,Y4),andsoon(oraveragingisused)ChromaSubsamplingTobeginwit38ChromaSubsamplingThescheme“4:1:1”subsampleshorizontallybyafactorof4.Thescheme“4:2:0”subsamplesinboththehorizontalandverticaldimensionsbyafactorof2.Theoretically,anaveragechromapixelispositionedbetweentherowsandcolumnsasshownFig.5.6.Scheme4:2:0alongwithotherschemesiscommonlyusedinJPEGandMPEG(seelaterchaptersinPart2).ChromaSubsamplingThescheme“39ChromaSubsamplingFig.5.6:ChromasubsamplingChromaSubsamplingFig.5.6:Ch40CCIRStandardsforDigitalVideoCCIRistheConsultativeCommitteeforInternationalRadio,andoneofthemostimportantstandardsithasproducedisCCIR-601,forcomponentdigitalvideo.ThisstandardhassincebecomestandardITU-R-601,aninternationalstandardforprofessionalvideoapplicationsadoptedbycertaindigitalvideoformatsincludingthepopularDVvideo.TheCCIR601standardusesaninterlacedscan,soeachfieldhasonlyhalfasmuchverticalresolution(e.g.,240linesinNTSC).Table5.3showssomeofthedigitalvideospecifications,allwithanaspectratioof4:3.CCIRStandardsforDigitalVid41CCIRStandardsforDigitalVideoCIFstandsforCommonIntermediateFormatspecifiedbytheCCITT.TheideaofCIFistospecifyaformatforlowerbitrate.CIFisaboutthesameasVHSquality.Itusesaprogressive(non-interlaced)scan.AlltheCIF/QCIFresolutionsareevenlydivisibleby8,andallexcept88aredivisibleby16;QCIFstandsfor“Quarter-CIF”.itprovidesconvenienceforblock-basedvideocodinginH.261andH.263whichwillbediscussedlaterinChapter10.CCIRStandardsforDigitalVid42CCIRStandardsforDigitalVideoNote,CIFisacompromiseofNTSCandPALinthatitadoptsthe‘NTSCframerateandhalfofthenumberofactivelinesasinPAL.Table5.3:DigitalvideospecificationsCCIR601525/60NTSCCCIR601625/50PAL/SECAMCIFQCIFLuminanceresolution720x480720x576352x288176x144Chrominanceresolution360x480360x576176x14488x72ColorSubsampling4:2:24:2:24:2:04:2:0Fields/sec60503030InterlacedYesYesNoNoCCIRStandardsforDigitalVid43HDTV(HighDefinitionTV)ThemainthrustofHDTV(HighDefinitionTV)isnottoincreasethe“definition”ineachunitarea,butrathertoincreasethevisualfieldespeciallyinitswidth.ThefirstgenerationofHDTVwasbasedonananalogtechnologydevelopedbySonyandNHKinJapaninthelate1970s.MUSE(MUltiplesub-NyquistSamplingEncoding)wasanimprovedNHKHDTVwithhybridanalog/digitaltechnologiesthatwasputinuseinthe1990s.Ithas1,125scanlines,interlaced(60fieldspersecond),and16:9aspectratio.SinceuncompressedHDTVwilleasilydemandmorethan20MHzbandwidth,whichwillnotfitinthecurrent6MHzor8MHzchannels,variouscompressiontechniquesarebeinginvestigated.ItisalsoanticipatedthathighqualityHDTVsignalswillbetransmittedusingmorethanonechannelevenaftercompression.HDTV(HighDefinitionTV)Them44AbriefhistoryofHDTVevolutionIn1987,theFCCdecidedthatHDTVstandardsmustbecompatiblewiththeexistingNTSCstandardandbeconfinedtotheexistingVHF(VeryHighFrequency)andUHF(UltraHighFrequency)bands.In1990,theFCCannouncedaverydifferentinitiative,i.e.,itspreferenceforafull-resolutionHDTV,anditwasdecidedthatHDTVwouldbesimultaneouslybroadcastwiththeexistingNTSCTVandeventuallyreplaceit.AbriefhistoryofHDTVevolut45AbriefhistoryofHDTVevolutionWitnessingaboomofproposalsfordigitalHDTV,theFCCmadeakeydecisiontogoall-digitalin1993.A“grandalliance”wasformedthatincludedfourmainproposals,byGeneralInstruments,MIT,Zenith,andAT&T,andbyThomson,Philips,Sarnoffandothers.ThiseventuallyledtotheformationoftheATSC(AdvancedTelevisionSystemsCommittee)itisresponsibleforthestandardforTVbroadcastingofHDTV.In1995theU.S.FCCAdvisoryCommitteeonAdvancedTelevisionServicerecommendedthattheATSCDigitalTelevisionStandardbeadopted.AbriefhistoryofHDTVevolut46HDTVStandardThestandardsupportsvideoscanningformatsshowninTable5.4.Inthetable,“I”meaninterlacedscanand“P”meansprogressive(non-interlaced)scan.#ofActivePixelsperline#ofActiveLinesAspectRatioPictureRate1,9201,08016:960I30P24P1,28072016:960P30P24P70448016:9&4:360I60P30P24P6404804:360I60P30P24PTable5.4:AdvancedDigitalTVformatssupportedbyATSCHDTVStandardThestandardsupp47HDTVForvideo,MPEG-2ischosenasthecompressionstandard.Foraudio,AC-3isthestandard.Itsupportstheso-called5.1channelDolbysurroundsound,i.e.,fivesurroundchannelsplusasubwooferchannel.ThesalientdifferencebetweenconventionalTVandHDTV:HDTVhasamuchwideraspectratioof16:9insteadof4:3.HDTVmovestowardprogressive(non-interlaced)scan.Therationaleisthatinterlacingintroducesserratededgestomovingobjectsandflickersalonghorizontaledges.HDTVForvideo,MPEG-2ischose48HDTVTheFCChadplannedtoreplaceallanalogbroadcastserviceswithdigitalTVbroadcastingbytheyear2009.Theservicesprovidedwillinclude:SDTV(StandardDefinitionTV):thecurrentNTSCTVorhigherEDTV(EnhancedDefinitionTV):480activelinesorhigheri.e.,thethirdandfourthrowsinTable5.4.HDTV(HighDefinitionTV):720activelinesorhigherHDTVTheFCChadplannedtorep49HDTVHDTV格式高清晰度电视(highdefinitiontelevision，HDTV)是具有正常视力的观众可得到与观看原始景物时的感受几乎相同的数字电视。通常认为，在观众与显示屏之间的距离等于3倍显示屏高度的情况下就可获得这种感受ATSCHDTV是ATSC定义的数字电视格式中的一个子集，由6种格式组成，见表9-12。ATSC还开发并通过了可为采用25Hz和50Hz刷新频率的国家使用的另行标准HDTV的电视图像有如下特点：(1)HDTV屏幕的宽高比均为16:9；(2)电视画面可用1920×1080像素和1280×720像素两种尺寸；(3)扫描方式为隔行扫描或逐行扫描HDTVHDTV格式50HDTV欧洲DVB标准对HDTV电视图像格式的定义与ATSCHDTV格式基本相同，见表9-12，只是电视画面的刷新频率不同。该标准既可用于刷新频率为25Hz和50Hz的国家，也可用于刷新频率为30Hz和60Hz的国家HDTV欧洲DVB标准对HDTV电视图像格式的定义与ATSC515.4 FurtherExplorationLinkshttp://www.cs.sfu.ca/mmbook/furtherv2/node5.htmlgivenforthisChapteronthetextwebsiteinclude:TutorialsonNTSCtelevisionTheofficialATSChomepageThelatestnewsonthedigitalTVfrontIntroductiontoHDTVTheofficialFCC(FederalCommunicationsCommission)homepage5.4 FurtherExplorationLinks52Assignments5.5Ex16910Assignments5.5Ex53Chapter5

FundamentalConceptsinVideo5.1 TypesofVideoSignals5.2 AnalogVideo5.3 DigitalVideo5.4 FurtherExplorationChapter5

FundamentalConcepts545.1 TypesofVideoSignalsComponentvideo（分量视频）Compositevideo（复合视频）S-Video（超视频）5.1 TypesofVideoSignalsCom555.1 TypesofVideoSignalsComponentvideoHigher-endvideosystemsmakeuseofthreeseparatevideosignalsforthered,green,andblueimageplanesEachcolorchannelissentasaseparatevideosignal.MostcomputersystemsuseComponentVideo,withseparatesignalsforR,G,andBsignals.Foranycolorseparationscheme,ComponentVideogivesthebestcolorreproductionsincethereisno“crosstalk”betweenthethreechannels.ThisisnotthecaseforS-VideoorCompositeVideo,discussednext.Componentvideo,however,requiresmorebandwidthandgoodsynchronizationofthethreecomponents.5.1 TypesofVideoSignalsCom565.1 TypesofVideoSignalsComponentvideo5.1 TypesofVideoSignalsCom57CompositeVideo—OneSignalCompositevideo

color(“chrominance”)andintensity(“luminance”)signalsaremixedintoasinglecarrierwave.Chrominanceisacompositionoftwocolorcomponents(IandQ,orUandV).InNTSCTV,e.g.,IandQarecombinedintoachromasignal,andacolorsubcarrieristhenemployedtoputthechromasignalatthehigh-frequencyendofthesignalsharedwiththeluminancesignal.Thechrominanceandluminancecomponentscanbeseparatedatthereceiverendandthenthetwocolorcomponentscanbefurtherrecovered.CompositeVideo—OneSignalCo58CompositeVideo—OneSignalCompositevideoWhenconnectingtoTVsorVCRs,CompositeVideousesonlyonewireandvideocolorsignalsaremixed,notsentseparately.Theaudioandsyncsignalsareadditionstothisonesignal.Sincecolorandintensityarewrappedintothesamesignal,someinterferencebetweentheluminanceandchrominancesignalsisinevitable.CompositeVideo—OneSignalCo59CompositeVideo—OneSignalCompositevideoCompositeVideo—OneSignalCo60S-Video—TwoSignalsS-Videoasacompromise,(separatedvideo,orSuper-video,e.g.,inS-VHS)usestwowires,oneforluminanceandanotherforacompositechrominancesignal.Asaresult,thereislesscrosstalkbetweenthecolorinformationandthecrucialgray-scaleinformation.S-Video—TwoSignalsS-Video61S-Video—TwoSignalsS-VideoThereasonforplacingluminanceintoitsownpartofthesignalisthatblack-and-whiteinformationismostcrucialforvisualperception.Infact,humansareabletodifferentiatespatialresolutioningrayscaleimageswithamuchhigheracuitythanforthecolorpartofcolorimages.Asaresult,wecansendlessaccuratecolorinformationthanmustbesentforintensityinformation—wecanonlyseefairlylargeblobsofcolor,soitmakessensetosendlesscolordetail.S-Video—TwoSignalsS-Video62S-Video—TwoSignalsS-Videosmallroundconnectorwithtwoseparatevideosignals,onecarryingbrightness(luminance),theothercarryingcolor(chroma).AlsoreferredtoasY/CvideoS-Video—TwoSignalsS-Video63电视扫描和同步扫描分类非隔行扫描（逐行扫描）(progressivescanning)计算机显示器隔行扫描(interlacedscanning)电视电视扫描和同步扫描分类645.2 AnalogVideoInTV,andinsomemonitorsandmultimediastandardsaswell,anothersystem,called“interlaced”scanningisused:Theodd-numberedlinesaretracedfirst,andthentheeven-numberedlinesaretraced.Thisresultsin“odd”and“even”fields—twofieldsmakeuponeframe.Infact,theoddlines(startingfrom1)endupatthemiddleofalineattheendoftheoddfield,andtheevenscanstartsatahalf-waypoint.5.2 AnalogVideoInTV,andin655.2 AnalogVideoFigure5.1showstheschemeused.Firstthesolid(odd)linesaretraced,PtoQ,thenRtoS,etc.,endingatT;thentheevenfieldstartsatUandendsatV.ThejumpfromQtoR,etc.inFigure5.1iscalledthehorizontalretrace,duringwhichtheelectronicbeamintheCRTisblanked.ThejumpfromTtoUorVtoPiscalledtheverticalretrace.Fig.5.1:Interlacedrasterscan5.2 AnalogVideoFigure5.1sh665.2 AnalogVideo5.2 AnalogVideo675.2 AnalogVideoBecauseofinterlacing,theoddandevenlinesaredisplacedintimefromeachother—generallynotnoticeableexceptwhenveryfastactionistakingplaceonscreen,whenblurringmayoccur.Forexample,inthevideoinFig.5.2,themovinghelicopterisblurredmorethanisthestillbackground.5.2 AnalogVideoBecauseofin685.2 AnalogVideoFig.5.2:Interlacedscanproducestwofieldsforeachframe.(a)Thevideoframe,(b)Field1,(c)Field2,(d)DifferenceofFields(a)(b)(c)(d)5.2 AnalogVideoFig.5.2:Int695.2 AnalogVideoSinceitissometimesnecessarytochangetheframerate,resize,orevenproducestillsfromaninterlacedsourcevideo,variousschemesareusedto“de-interlace”it.Thesimplestde-interlacingmethodconsistsofdiscardingonefieldandduplicatingthescanlinesoftheotherfield.Theinformationinonefieldislostcompletelyusingthissimpletechnique.Othermorecomplicatedmethodsthatretaininformationfrombothfieldsarealsopossible.5.2 AnalogVideoSinceitiss70TVStandardsNTSC美国、加拿大等大部分西半球国家，以及日本、韩国、菲律宾PAL德国、英国等一些西欧国家，及中国、朝鲜等国家SECAM法国、及东欧国家TVStandardsNTSC71WorldTVStandards

NTSCPALSECAMPAL/SECAMUnknownWorldTVStandards

NTSCPALSECA72NTSCVideoNTSC(NationalTelevisionSystemCommittee)TVstandardusesthefamiliar4:3aspectratio(i.e.,theratioofpicturewidthtoitsheight)anduses525scanlinesperframeat30framespersecond(fps).ItismostlyusedinNorthAmericaandJapan.NTSCVideoNTSC(NationalTelev73NTSCVideoFeaturesofNTSCNTSCfollowstheinterlacedscanningsystem,andeachframeisdividedintotwofields,with262.5lines/field.Thusthehorizontalsweepfrequencyis525×29.97≈15,734lines/sec,sothateachlineissweptoutin1/15.734×103sec≈63.6μsec.Sincethehorizontalretracetakes10.9μsec,thisleaves52.7μsecfortheactivelinesignalduringwhichimagedataisdisplayed(seeFig.5.3).NTSCVideoFeaturesofNTSC74NTSCVideoFig.5.4showstheeffectof“verticalretrace&sync”and“horizontalretrace&sync”ontheNTSCvideoraster.Fig.5.4:Videoraster,includingretraceandsyncdataNTSCVideoFig.5.4showsthee75NTSCVideoVerticalretracetakesplaceduring20linesreservedforcontro