#7: photorealism · review: classical rendering “top-down” (phong, et al.) • assumes...
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#7:Photorealism
TheHighEnd
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ElementsoftheFinalImage
• Geometry• Lights• Materiality• Viewpoints&focalpoints• Cameras&op5cs• Rendering:color&light
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SyntheAcCameraIssues
“thefamiliar”
VRay“EV”
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SyntheAcCamera
“beyondourscope”
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Rendering:Color&Light
“it’saboutlight&surface”
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Review:ClassicalRendering
“Top-down”(Phong,etal.)• Assumesperfectlydiffusesurfaces• Worksfromgeometrydatatoscreen• Asidefromshadows,ignoresothergeometry• DoesnotrenderindirectilluminaAon,colorbleed,ambientocclusion,causAcs,ormostspeculareffects(refracAonandreflecAon).
• SoluAonisview-dependent
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Wait!Whatdowemeanby…
• IndirectilluminaAon• Colorbleed• Speculareffects:ReflecAon&RefracAon• CausAcs• Ambientocclusion• View-independence
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Indirectillumina5on
KimbellArtMuseum,LouisKahn,1972
Lightsourceinvisible.LightdistributedbydiffusereflecAonoffsurfaces.
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ColorBleed
Whatcoloristhiswall?
Whatcoloristhiswall?
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ColorBleed
Theresultofdiffuseinter-reflecAon.
DiffusereflecAonofcolorfromadjacentsurfaces.
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SpecularEffectsReflecAon
Specular(mirror-like)reflecAonofgeometryinasurface.
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SpecularEffectsRefracAon
Lightbentduringtransmissionthroughtransparentobjects.
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Caus5csRefractedlight
DiffuseSurface
photograph
Earlyraytracing
DiffusereflecAonoflightAFTERspecularrefracAon.
Theshadowdoesn’tshowcausAcfromglass.
Thelightpa]ernonthetableisacaus.c.
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AmbientOcclusion
Closelyspacedsurfacesblock(occlude)ambientlightentry,makingdarkseamsandjoints.
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AmbientOcclusion
WithAmbientOcclusionWithoutAmbientOcclusion
Chaos-grou
pgraphic
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Whatis“View-dependence”
• LightdistribuAonintherealworlddoesnotdependonthecameraposiAon(noflash!).
• Arenderingalwayshasgeometricaldependenciesonviewpoint/etc.
• GiventhecostofcompuAnglightdistribuAon,itwouldbeniceifasinglelighAngsoluAoncouldbesharedbyaseriesofrenderings,asinananimaAon.
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Now:ImprovingClassicalRendering
• AnA-aliasbysuper-sampling@3:1or4:1• AnA-aliastexturestoo• Useextra“fill”lights(noshadows)
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Let’stryadifferentapproachLightreflectsin“infinite”ways,butthereareafinitenumberofscreenpixelsand
modelsurfaces.
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RealLight:
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FirstApproximaAon:RayTracing“individualrays”AlmostRealLight
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Ray-SurfaceInterac5ons
Chaos-grou
pgraphic
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Lighttravelsinstraightlines
• Toreachtheeye,itcamefromthepixel• Toreachthepixelitcame“from”themodel• Eachbounceisspecular• Workbackwards• Eachpixelisseparate
• AddupthecontribuAonsofeachbounce.
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RayTracing“scorecard”
• ReflecAon✔• RefracAon✔• IndirectIlluminaAon✖• ColorBleed ✖
• CausAcs✖
• AmbientOcclusion✖
- View-dependentsoluAon
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GePngaGoodRay-tracing
• AnA-aliasbysuper-sampling@3:1or4:1• AnA-aliastexturestoo• Set“maximum-bounces”higher(note,bounces=0/1->“hiddensurfaces”)
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TheFEM“energyexchange”model
Correctindiffuseenvironments
DevelopedatCornellUniversity
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DevelopedatCornellUniversity
Radiosityenergyexchange
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Radiosity:energyexchange
• Dividesurfaces• Compute‘anglefactors’• DistributedirectilluminaAon• ComputebounceredistribuAon.
• Subdividehigh-contrastedges.
• SmoothresulAngimage
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Radiosity“scorecard”• ReflecAon✖• RefracAon≈• IndirectIlluminaAon✔• ColorBleed✔
• CausAcs✖
• AmbientOcclusion✖
+ SoluAonisview-independent
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GePngGoodRadiosityResult
• AnA-aliasbysuper-sampling@3:1or4:1• AnA-aliastexturestoo• Set“%energydistribuAon”tohighnumber(e.g.99%)
• CombinewithRay-TracingforreflecAon&refracAoneffects
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GePngBothSpecularandDiffuseEffectsinOneRendering?
Path-Tracing:Enhancedray-tracingWorktheproblemfrombothends:
1.Tracelightfromsourcestosurfaces2.Back-tracelightfromeyeintoscene.
- AND-3.ComputediffusereflecAonsbyusingstaAsAcal(“sampling”)approach
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PathTracing:TwoPasses
Chaos-grou
pgraphic
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1.TraceForwardfromtheLights• Send“photons”(lightrays)intothescene(distributeaccurately)
• Wheneveraphotonstrikesasurface,recordwhere&inwhatdirecAonina“photonmap”
• UsesurfacequaliAes(BRDF)tocomputeprobablebouncedirecAon.
• Bounce• Repeat
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2.TraceBackwardsfromtheEye
• “Back-trace”rayintoscene• Atsurfaces,searcharoundinphotonmap.• Computeeffectofphotons.• Ifsurfaceisspecular,followclassicalbounce
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Review…
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ImprovingPathTracing
• AnA-aliasbysuper-sampling@3:1or4:1• AnA-aliastexturestoo• Increasenumberofphotonsinphase1• Increasenumberofbouncesinphase2• Decreasesearchradiustosharpenimage• Increaseimagesamplestoimprovedetail
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…umm..BRDF?
Realsurfacesbouncelightincomplexwaysthatdependonthewavelengthofthelight,theangleofincidence,etc.ThefuncAonthatdescribeshowmuchlightgoeswhereiscalled…
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“BRDF”
BidirecAonalReflectanceDistribuAonFuncAon(wherereflectedlightreallygoes)
Thespecular-ishbounce
Thediffuse-ishbounce
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#7:Photorealism
NotTheEnd