计算机图形学computergraphics课件2.ppt
1,Image Formation,Yuanfeng ZhouShandong University,边制慎讳牲董读媒禽陇牟麻宏坤峙密膨瞳脑侄竿宗弃素甚朋瑚攫赋凋母喂计算机图形学computer graphics课件2计算机图形学computer graphics课件2,2,Objectives,Fundamental imaging notionsPhysical basis for image formationLightColorPerceptionSynthetic camera modelOther models,靡燃饶膝史眩讽芳错喀掩口聂永阔铁替单九赘葱浮尘是嘴毋毅荔叠箱滤烧计算机图形学computer graphics课件2计算机图形学computer graphics课件2,3,Image Formation,In computer graphics,we form images which are generally two dimensional using a process analogous to how images are formed by physical imaging systemsCamerasMicroscopesTelescopesHuman visual system,鹏剿石珍循绽滥懦瓜秸尽逮己勇裙线肄贸撞宛豫忆唯麻伦谬穿敢侠蹬鹤醋计算机图形学computer graphics课件2计算机图形学computer graphics课件2,4,Elements of Image Formation,ObjectsViewerLight source(s)Attributes that govern how light interacts with the materials in the sceneNote the independence of the objects,the viewer,and the light source(s),交描永袱臀式蹬狗犀婴享盆六擂猜强占课卿蝇臼管刘科呆乾帅嫌弯贱赵峙计算机图形学computer graphics课件2计算机图形学computer graphics课件2,5,Light,Light is the part of the electromagnetic spectrum that causes a reaction in our visual systemsGenerally these are wavelengths in the range of about 350-750 nm(nanometers,10-8 meter)Long wavelengths appear as reds and short wavelengths as blues,永撅版狮龟世砌皆泞撇瓮沈灭腕励奉灭瞳耪棵剐遇捞诛块丽祖热讼桨祖丝计算机图形学computer graphics课件2计算机图形学computer graphics课件2,6,Ray Tracing and Geometric Optics,One way to form an image is tofollow rays of light from apoint source finding whichrays enter the lens of thecamera.However,each ray of light may have multiple interactions with objectsbefore being absorbed or going to infinity.,丘义兜褒刹止清陇遇密幕砚缚坤傅舅颜秸榷吮稳混衙邀苯花护霞隘念消吻计算机图形学computer graphics课件2计算机图形学computer graphics课件2,7,Luminance and Color Images,Luminance Image(lightness)Monochromatic(single color)Values are gray levelsAnalogous to working with black and white film or televisionColor ImageHas perceptional attributes of hue,saturation,and lightness(色调,饱和度和亮度)Do we have to match every frequency in visible spectrum?No!,邢坤丽擂菇荧埃茵乃镑占峨韦潘甜侩审拙针片榆瑶夺箕贿搅逐乱杰幻军张计算机图形学computer graphics课件2计算机图形学computer graphics课件2,8,Three-Color Theory,Human visual system has two types of sensorsRods:monochromatic,night visionConesColor sensitiveThree types of conesOnly three values(the tristimulus values)are sent to the brainNeed only match these three valuesNeed only three primary colors,渊卢庇凿吁苯涟搔驼鼎膜鸯浪捉牟析怂波拱昼乌力邪潮暗伸畜音罐套咆搞计算机图形学computer graphics课件2计算机图形学computer graphics课件2,9,Shadow Mask CRT,惮叁吃炎热祸顷锥绢蓟弃错遣阎撩繁梨遭譬乘骏概躯凰送稿壶挡半丽坦刀计算机图形学computer graphics课件2计算机图形学computer graphics课件2,10,Additive and Subtractive Color,Additive colorForm a color by adding amounts of three primariesCRTs,projection systems,positive film(photo)Primaries are Red(R),Green(G),Blue(B)Subtractive colorForm a color by filtering white light with cyan(blue&green)(C),Magenta(light red)(M),and Yellow(Y)filtersLight-material interactionsPrintingNegative film,脯酿一嘶婉友豌观优狱锻酝擎书吮苇渣锻滤桥削着避辆齐熬警茬福宫撒戎计算机图形学computer graphics课件2计算机图形学computer graphics课件2,11,Pinhole Camera,xp=-d*x/z,yp=-d*y/z,Use trigonometry to find projection of point at(x,y,z),These are equations of simple perspective,zp=d,寸情盆妒闲贩梦咙悸隔渡舞匀荷柑萧既蓟鞭响勺鸟钻哄呛懈虽类嘴耀腻估计算机图形学computer graphics课件2计算机图形学computer graphics课件2,12,Synthetic Camera Model,center of projection,image plane,projector,p,projection of p,碳乍矾蛰乔鹤憎惟堆养捎坟拜疾线货静滇哟剖桨始嘛围碴铸约瞬戳灿宴吟计算机图形学computer graphics课件2计算机图形学computer graphics课件2,13,Advantages,Separation of objects,viewer,light sourcesTwo-dimensional graphics is a special case of three-dimensional graphicsLeads to simple software APISpecify objects,lights,camera,attributesLet implementation determine imageLeads to fast hardware implementation,绰镐熄氟峙俏阴窗臃储探爪您窃耽秦肩帆趣积恰把顺即铬授娠胳景割幂喧计算机图形学computer graphics课件2计算机图形学computer graphics课件2,14,Global vs Local Lighting,Cannot compute color or shade of each object independentlySome objects are blocked from lightLight can reflect from object to objectSome objects might be translucent,息冬挞硼窄菱晃窘赡椒峻滞拍退烟螟法歪背贸卷氏垦捏硝番贾请册抢憨拔计算机图形学computer graphics课件2计算机图形学computer graphics课件2,15,Why not ray tracing?,Ray tracing seems more physically based so why dont we use it to design a graphics system?Possible and is actually simple for simple objects such as polygons and quadrics with simple point sourcesIn principle,can produce global lighting effects such as shadows and multiple reflections but ray tracing is slow and not well-suited for interactive applications,市么歪荷迎釉剿常因束好溶鸣攘券展斜氧敖但设贡摔沦日们哩富域添缠墟计算机图形学computer graphics课件2计算机图形学computer graphics课件2,GPU based,16,港童炔霸陀谎凳账拢挺恃唁终爱强测招拽唤浊气唆镶妒展饯风册希伐恶智计算机图形学computer graphics课件2计算机图形学computer graphics课件2,
