#7: Photorealism · Review: Classical Rendering “Top-down” (Phong, et al.) • Assumes...

#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