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Ch3GraphicsandImageDataRepresentations1.Brieflyexplainwhyweneedtobeabletohavelessthan24-bitcolorandwhythismakesforaproblem.Generally,whatdoweneedtodotoadaptivelytransform24-bitcolorvaluesto8-bitones?Answer:Maynotbeabletohandlesuchlargefilesizesornothave24-bitdisplays.Thecolorswillbesomewhatwrong,however.Weneedtoclustercolorpixelssoastobestusethebitsavailabletobeasaccurateaspossibleforthecolorsinanimage.Inmoredetail:varianceminimizationquantization–vmquant.mMinimumvariancequantizationallocatesmoreoftheavailablecolormapentriestocolorsthatappearfrequentlyintheinputimageandallocatesfewerentriestocolorsthatappearinfrequently.Thereforeifthereareforexamplemanyreds,asinaredapple,therewillbemoreresolutionintheredpartofthecolorcube.AnexcellentimplementationofthisideaisWu’sColorQuantizer(seeGraphicsGemsvol.II,pp.126-133).2.Supposewedecidetoquantizean8-bitgrayscaleimagedowntojust2bitsofaccuracy.Whatisthesimplestwaytodoso?Whatrangesofbytevaluesintheoriginalimagearemappedtowhatquantizedvalues?Answer:0to6364to127128to191192to255Thenreconstructionvaluesshouldbetakenasthemiddleoftheseranges;i.e.,32961602243.Supposewehavea5-bitgrayscaleimage.Whatsizeofordereddithermatrixdoweneedtodisplaytheimageona1-bitprinter?Answer:2ˆ5=32levels˜=nˆ2+1withn=6;thereforeneedD(6)4.Supposewehaveavailable24bitsperpixelforacolorimage.However,wenoticethathumansaremoresensitivetoRandGthantoB—infact,1.5timesmoresensitivetoRorGthantoB.Howcouldwebestmakeuseofthebitsavailable?Answer:ratiois3:3:2,sousebits9:9:6forR:G:B.5.Atyourjob,youhavedecidedtoimpressthebossbyusingupmorediskspaceforthecompany’sgrayscaleimages.Insteadofusing8bitsperpixel,you’dliketouse48bitsperpixelinRGB.Howcouldyoustoretheoriginalgrayscaleimagessothatinthenewformattheywouldappearthesameastheyusedto,visually?Answer:48bitsRGBmeans16bitsperchannel:sore-storetheoldints,whichwere2ˆ8,asnewints2ˆ16.Butthenthenewvalueshavetobecreatedbymultiplyingtheoldvaluesby2ˆ8,sothate.g.amid-grayisstillamid-gray.Aswell,havetoduplicatetheoldgrayintoallthreeofR,G,B.6.ForthecolorLUTproblem,tryoutthemedian-cutalgorithmonasampleimage.Explainbrieflywhyitisthatthisalgorithm,carriedoutonanimageofredapples,putsmorecolorgradationintheresulting24-bitcolorimagewhereitisneeded,amongthereds.7.Writedownanalgorithm(pseudocode)forcalculatingacolorhistogramforRGBdata.Answer:inthist[256][256][256];imageisanappropriatestructwithintfieldsred,green,bluefori=0..(MAX_Y-1)forj=0..(MAX_X-1)R=image[x][y].red;G=image[x][y].green;B=image[x][y].blue;hist[R][G][B]++;Ch4ColorinImageandVideoExercise31.Considerthefollowingsetofcolor-relatedterms:(a)wavelength(b)colorlevel(c)brightness(d)whitenessHowwouldyoumatcheachofthefollowing(morevaguelystated)characteristicstoeachoftheaboveterms?(a)luminance＝＝)brightness(b)hue＝＝)wavelength(c)saturation＝＝)whiteness(d)chrominance＝＝)colorlevel2.Whatcolorisoutdoorlight?Forexample,aroundwhatwavelengthwouldyouguessthepeakpowerisforaredsunset?Forblueskylight?Answer:450nm,650nm.3.(a)Supposeimagesarenotgammacorrectedbyacamcorder.Generally,howwouldtheyappearonascreen?Answer:Toodarkatthelow-intensityend.(b)Whathappensifweartificiallyincreasetheoutputgammaforstoredimagepixels?(WecandothisinPhotoshop.)Whatistheeffectontheimage?Answer:Increasethenumberofbrightpixels—weincreasethenumberofpixelsthatmaptotheupperhalfoftheoutputrange.Thiscreatesalighterimage.–andincidentally,wealsodecreasehighlightcontrastandincreasecontrastintheshadows.Ch5FundamentalConceptsinVideo1.NTSCvideohas525linesperframeand63.6secperline,with20linesperfieldofverticalretraceand10.9sechorizontalretrace.(a)Wheredoesthe63.6seccomefrom?Answer:(b)Whichtakesmoretime,horizontalretraceorverticalretrace?Howmuchmoretime?Answer:2.Whichdoyouthinkhaslessdetectableflicker,PALinEuropeorNTSCisNorthAmerica?Justifyyourconclusion.Answer:PALcouldbebettersincemorelines,butisworsebecauseoffewerframes/sec.3.SometimesthesignalsfortelevisionarecombinedintofewerthanallthepartsrequiredforTVtransmission.(a)Altogether,howmanyandwhatarethesignalsusedforstudiobroadcastTV?Answer:5R,G,B,audio,sync;cansay“blanking”instead,too.(b)HowmanyandwhatsignalsareusedinS-Video?WhatdoesS-Videostandfor?Answer:Luminance+chrominance=2+audio+sync=4Separatedvideo(c)HowmanysignalsareactuallybroadcastforstandardanalogTVreception?Whatkindofvideoisthatcalled?Answer:1Composite4.OnesometimeshearsthattheoldBetamaxformatforvideotape,whichcompetedwithVHSandlost,wasactuallyabetterformat.Howwouldsuchastatementbejustified?Answer:Betamaxhasmoresamplesperline:500,asopposedto240.5.Wedon’tseeflickeronaworkstationscreenwhendisplayingvideoatNTSCframerate.Whydoyouthinkthismightbe?Answer:NTSCvideoisdisplayedat30framespersec,soflickerispossiblypresent.Nonetheless,whenvideoisdisplayedonaworkstationscreenthevideobufferisreadandthenrenderedonthescreenatamuchhigherrate,typicallytherefreshrate—60to90Hz—sonoflickerisperceived.(Andinfactmostdisplaysystemshavedoublebuffers,completelyremovingflicker:sincemainmemoryismuchfasterthanvideomemory,keepacopyofthescreeninmainmemoryandthenwhenwethisbufferupdateiscomplete,thewholeb