SIGGRAPH 2010

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionSIGGRAPH 2010Physically Based Shading Modelsin Film and Game Production- Practical implementation at tri-Ace

Yoshiharu GotandaResearch and Development Department tri-Ace, Inc.

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game Production

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionHistoryNon-physical Blinn-Phong model, as commonly used in games

n : Shininess (cosine power)Rd : Diffuse colorRs : Specular colorF0 : Fresnel coefficientG : Geometry Attenuation


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionDifficulty with ad-hoc modelsArtists tend to have difficulty matching physical accurate valuesEven if one object has a 1,000x stronger specular than another, they dont set those valuesDifficult to see this dynamic difference in Low Dynamic Range (LDR) imagesProblem with Schlicks approximation in production

Wrong setting


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionProblem with Schlicks approximationFresnel term is implemented with Schlicks approximationFor Blinn model shaders and Fresnel shadersPreviously, artists directly set f0 parameter in a toole.g. A material has a refractive index of 1.5, setting f0 to 0.04 is correct and meansReflection ratio between normal and glancing direction is 25But


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionProblem with Schlicks approximation25x specular variance is not intuitively acceptable by artists25x specular variancef0 = 0.04f0 = 0.04 with a refractive index of 1.5


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionProblem with Schlicks approximationThen, an artist incorrectly sets 0.3 or 0.5 based on their intuitionConsequently normal reflectance becomes strongerSpecular looks too strong compared to realityThe artist reduces specular intensitySpecular looks too weak at glancing anglesSpecular highlight on the edge with back lighting cant be represented


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionIf f0 is too largeToo weak specular on edgeToo strong specular in normal directionToo small specular valueCorrectToo high Fresnel value


Our solutionParameters for Fresnel are changed to use eitherComplex refractive indices OR Prebuilt material templates



SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionWhy physically based?Artists can more easily manipulate the parametersFewer parameters and texturesShader guarantees physically correct appearance


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionOur BRDF modelBlinn-Phong based BRDFOur customized Blinn-Phongn : Shininess (cosine power)Rd : Diffuse albedoF0 : Normal Specular ReflectanceDetails on how we derived this expression are in the course notes

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionNormalization Factor ApproximationThe result is expensive for real-timeTherefore, we approximate it with a linear function insteadNormalization Factorshininess


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionFinal ModelDiffuse term is also approximated for performanceOur customized model


ComparisonSIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAd-hocOur spectral model

Comparison - shininess map onlySIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAd-hocOur model

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionComparison - reflectance map onlyAd-hoc with specular color mapOur modelOur spectral model

ComparisonSIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAd-hocOur modelAd-hocOur Spectral model

Comparison - shininess map onlySIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAd-hocOur modelAd-hocSpectral model

Comparison - metalSIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAluminumCopperTitaniumOur spectral modelOur metal model

Other shader variationsSIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionMarschnerKajiya-Kay

Other shader variationsSIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAshikhmin-ShirleyOur anisotropic model

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionProblem with ambient lightingEven with physically-based shading models, ambient lighting is still not physically-basedAmbient term is typically computed as a constantBased on a diffuse only termBased on arbitrary value between diffuse and specular termsIdeally, ambient lighting should be computed as spherical area lighting with a proper BRDF

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionProblem with ambient lightingQuality degrades in scenes mainly lit by ambient lightingShadowed areasInside a house lit only by daylight (no artificial lights)Cloudy outside


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAmbient lighting improvementsSpherical Harmonic lightingIrradiance or SH volumesImage based lighting (environment mapping)Ambient occlusion

Ambient Occlusion OFFAmbient Occlusion ON


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionProblem with ambient lighting


Manual solutionsArtists have fought against the problem by handPut secondary lightsRim light, fill lightBuild a special shaderSolve the problem using our highly flexible shader systemNon-physical solutionSIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game Production

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionManual solutionsNo solutionSpecial shader by an artist (No BRDF solution)Manual lighting

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAmbient BRDFA new BRDF model for ambient shadingIn order to improve quality of ambient shadingSpecular and diffuse components are computed taking into account ambient lightingAmbient term is no longer a constantAmbient lighting is regarded as area lighting


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionBRDF integral for ambient shadingIntegrate a BRDF model over hemisphereThe results are stored in a linear (non-swizzled) volume textureU (EN) : dot product of eye and normal vectorV shininessW f0


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionAmbient BRDF ShadingUse the volume texture in pixel shaderSpecular term is computed as texture fetchThe texture directly stores the specular termDiffuse term is Rd*(1 specular)Ideally diffuse term should be stored in the texture for accurate resultIn our case, diffuse term is approximated for performance


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionColor terms for Ambient BRDFFor SH lightingDiffuse lighting color is computed with a normal vectorSpecular lighting color is computed with a reflection vectorNo specular cosine lobe is consideredCoarsely approximated


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionColor terms for Ambient BRDFFor image based lightingDiffuse lighting color is computed withDiffuse cube mapSH vector (computed from an environment map)Specular lighting color is computed withPre-filtered mipmapped environment map


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionResult - Ambient + Ambient BRDF


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionComparison Ambient BRDFOFFON

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionPerformanceUnit : ms

Ad-hoc modelCustomized modelAnisotropic modelSpectral modelMetal modelAshikhminAmbient BRDF off3.133.714.674.023.485.15Ambient BRDF onN/A4.375.134.613.835.76

SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionFinal comparison 1Our physically based modelsAd-hoc model


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionConclusionA physically based model isEasy to use for artistsEasy to get photo-realistic resultsReasonable to use in terms of performanceAmbient shading improvement is importantImprovement is possible in real-time


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionThanks to the following peopleR&D programmers:Tatsuya Shoji, Bart Sekura and Elliott DavisArtists:Kenichi Kanekura, Kazuki Shigeta, Kenichi Kaneko and Ryo MizukamiSpeakers for this course


SIGGRAPH 2010 Course: Physically Based Shading Models in Film and Game ProductionThankshtttp://research.tri-ace.com


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SIGGRAPH 2010