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