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1、ComputerGraphicsShi-MinHuTsinghuaUniversityOverviewofTodayIntroductionofsomeimportantconceptsinGraphicsColorImage&Pixel(图像,像素)TriangleMesh(三角网格)Lighting&Shading（光照和着色）OpenGLColorPerceptionWhatisColor?Colorsarethesensationsthatarisefromlightenergyofdifferentwavelengthswearesensitivefromelectroma
2、gneticwave(电磁波)about380to760nmSpectralDistributionofLight“Light”isamixtureofmanywavelengthseachwithsomeintensityspectraldistribution:(光谱分布) intensityasafunctionofwavelengthovertheentirespectrumcolorscanberepresentedassuchdistributionfunctionColorspaceHumanvisionsystemThreetypesofcones256graylev
3、elsaremuchmorethanoureyescandistinguishRGBcolorspaceRepresentcolorsasRGBtriples(r,g,b)Usually,eachcolorvaluehas256differentgrayscales.RGBColorSpaceRepresentcolorsasRGBtriples(r,g,b)performalmostalloperationsoneachchannelseparatelyusually,eachcolorvalueisafloatvaluerangefrom0to1,or0-255ifweareus
4、ing8bitintegers.ThemostwidelyusedcolorspaceRGBColorSpacecolorascombinationsofthreeprimariesestablished3specialcolors(red,green,blue)C=rR+gG+bBandwhydidwepickred,green,andblue?essentiallybecauseofthestructureofourvisualsystemroughlycorrespondtopeaksofconeresponsecurveDemoRGBcolorspaceRGBColorSpa
5、ceSomecolorscannotbewrittenascombinationsofRGBtriples,becausesomepartsoftheredcurveisnegativeOverlapofconeresponsecurvesSomemorelimitationswillbeshownlater.OtherColorSpacesCMYHSVCIEXYZ…CMYWecanchoosedifferentlightingunittorepresenteachindividualRGBcolorcomponents.Thisisusedinmonitor,LCD,andmany
6、otherdevices.Inthefieldofcolorprinting,paintcanonlyabsorblightsandtheycannotproducelightingthemselves.SoweintroduceCMYcolorspace.CMYTheothersetofprimariesbesidesRGBcyan,magenta,andyellow—complementsofred,green,blueThesearetheso-calledsubtractiveprimariesRGBareadditiveprimaries—startwithblack,ad
7、duptowhiteCMY—startwithwhiteandsubtractcolorsfromwhiteWhite:(0.0,0.0,0.0),black:(1.0,1.0,1.0)HSVTruecolorpictures:6,777,216possiblecolors.ControllingthishugeamountofpossibilitiesisalmostimpossiblewithouttheHSV.Applications:imagepr
