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1、外文資料及譯文原文：TelevisionVideoSignalsAlthoughover50yearsold,thestandardtelevisionsignalisstilloneofthemostcommonwaytotransmitanimage?Figure8.3showshowthetelevisionsignalappearsonanoscilloscope?Thisiscalledcompositevideo,meaningthatthereareverticalandhorizontalsynchronization(sy
2、nc)pulsesmixedwiththeactualpictureinformation.Thesepulsesareusedinthetelevisionreceivertosynchronizetheverticalandhorizontaldeflectioncircuitstomatchthevideobeingdisplayed.Eachsecondofstandardvideocontains30completeimages,commonlycalledframes,Avideoengineerwouldsaythateach
3、framecontains525lines,thetelevisionjargonforwhatprogrammerscallrows.Thisnumberisalittledeceptivebecauseonly480to486oftheselinescontainvideoinformation;theremaining39to45linesarereservedforsyncpulsestokeepthetelevision'scircuitssynchronizedwiththevideosignal.Standardtelevis
4、ionusesaninterlacedformattoreduceflickerinthedisplayedimage?Thismeansthatalltheoddlinesofeachframearetransmittedfirst,followedbytheevenlines.Thegroupofoddlinesiscalledtheoddfield,andthegroupofevenlinesiscalledtheevenfield.Sinceeachframeconsistsoftwofields,thevideosignaltra
5、nsmits60fieldspersecond?Eachfieldstartswithacomplexseriesofverticalsyncpulseslasting1.3milliseconds.Thisisfollowedbyeithertheevenoroddlinesofvideo.Eachlinelastsfor63.5microseconds,includinga10.2microsecondhorizontalsyncpulse,separatingonelinefromthenext.Withineachline,thea
6、nalogvoltagecorrespondstothegrayscaleoftheimage,withbrightervaluesbeinginthedirectionawayfromthesyncpulses?Thisplacethesyncbeyondtheblackrange.Invideojargon,thesyncpulsesaresaidtobeblackerthanblack..Thehardwareusedforanalog-to?digitalconversionofvideosignalsiscalledaframeg
7、rabber.Thisisusuallyintheformofanelectronicscardthatplugsintoacomputer,andconnectstoacamerathroughacoaxialcable?Uponcommandfromsoftware,theframegrabberwaitsforthebeginningofthenextframe,asindicatedbytheverticalsyncpulses.Duringthefollowingtwofields,eachlineofvideoissampled
8、manytimes,typically512,640or720samplesperline,at8bitspersample.Thesesamplesarestoredinmem
