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1、外文资料及译文原文：TelevisionVideoSignalsAlthoughover50yearsold,thestandardtelevisionsignalisstilloneofthemostcommonwaytotransmitanimage.Figure8.3showshowthetelevisionsignalappearsonanoscilloscope.Thisiscalledcompositevideo,meaningthatthereareverticalandhorizontalsynchron
2、ization(sync)pulsesmixedwiththeactualpictureinformation.Thesepulsesareusedinthetelevisionreceivertosynchronizetheverticalandhorizontaldeflectioncircuitstomatchthevideobeingdisplayed.Eachsecondofstandardvideocontains30completeimages,commonlycalledframes,Avideoengi
3、neerwouldsaythateachframecontains525lines,thetelevisionjargonforwhatprogrammerscallrows.Thisnumberisalittledeceptivebecauseonly480to486oftheselinescontainvideoinformation;theremaining39to45linesarereservedforsyncpulsestokeepthetelevision'scircuitssynchronizedwith
4、thevideosignal.Standardtelevisionusesaninterlacedformattoreduceflickerinthedisplayedimage.Thismeansthatalltheoddlinesofeachframearetransmittedfirst,followedbytheevenlines.Thegroupofoddlinesiscalledtheoddfield,andthegroupofevenlinesiscalledtheevenfield.Sinceeachfr
5、ameconsistsoftwofields,thevideosignaltransmits60fieldspersecond.Eachfieldstartswithacomplexseriesofverticalsyncpulseslasting1.3milliseconds.Thisisfollowedbyeithertheevenoroddlinesofvideo.Eachlinelastsfor63.5microseconds,includinga10.2microsecondhorizontalsyncpuls
6、e,separatingonelinefromthenext.Withineachline,theanalogvoltagecorrespondstothegrayscaleoftheimage,withbrightervaluesbeinginthedirectionawayfromthesyncpulses.Thisplacethesyncbeyondtheblackrange.Invideojargon,thesyncpulsesaresaidtobeblackerthanblack..Thehardwareuse
7、dforanalog-to-digitalconversionofvideosignalsiscalledaframegrabber.Thisisusuallyintheformofanelectronicscardthatplugsintoacomputer,andconnectstoacamerathroughacoaxialcable.Uponcommandfromsoftware,theframegrabberwaitsforthebeginningofthenextframe,asindicatedbythev
8、erticalsyncpulses.Duringthefollowingtwofields,eachlineofvideoissampledmanytimes,typically512,640or720samplesperline,at8bitspersample.Thesesamplesarestoredinmem
