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1、外文资料及译文原文：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
