Overview of Reflectance Models Focused on Car Paint Simulation Advisor: doc. RNDr. Roman...

Overview of Reflectance Models Focused on Car Paint Simulation

Advisor: doc. RNDr. Roman Ďurikovič, PhD.

RRóbert Smetanaóbert Smetana

Contents

• Goals of the Thesis• Paint Composition• BRDF Explained• Reflectance Models• Black Box Model• Conclusion

FMFI UK, June 2008 Róbert Smetana 2

Goals of the Thesis

• describe multi-lobe BRDF models• describe parameters they use• find parameters which are measureable under

industrial conditions• discuss most acceptable models


Paint Composition

• why is car paint modelling difficult?

• multiple layers• multiple types of flakes with different reflectance,

absorption and scattering properties


Different Coatings


Blue pigment only Metallic flakes Pearlescent flakes

* Rendered by Ďurikovič et al. in paper [ĎÁ07]

BRDF Explained

• Bidirectional Reflectance Distribution Function is one of a large family of light transport functions

• it expresses the ratio of reflected energy to total incident energy (radiance/irradiance)

• calculates only reflection, not scattering nor transmittance

• it is the main part of the rendering equation• spatially varying (6D) or homogenous (4D)


Multiple Lobes

• macro-appearance attributes• shade, glitter and gloss• more precise when described by own lobe


Reflectance Models

• Cook-Torrance (1981) – basic, can be extended

• He-Torrance (1991) – better Fresnel refl.• Ashikhmin et al. (2000) – better specular refl.• Ershov et al. (2001) – robust, sparkling effect • Ďurikovič et al. (2007) – better pigment depth

=> Black box model (2008) – all of themFMFI UK, June 2008 Róbert Smetana 8

Main Parameters

• Not measurable parameters– variation of flake orientation– highlight peak width– effective bulk reflectance of flakes– mean flake area

• Measurable parameters– thickness of paint layer– refractive indices– volumetric density of flakes


Summary

• more parameters = more detail, but more data• all of the models are good for industry

standards, but for specific conditions• for complex coatings the results of some

model can be visually implausible• it is expensive to test each model=> Black box model as an universal solution• part of work presented on SCCG 2008 poster


Black Box Model

• models focus on particular appearance attributes

• pigment producers don’t provide all the data• some parameters can be measured• some parameters can reverse engineered • combination of reviewed BRDFs can overcome

many limitations


Black Box Model


Black Box Model

Black Box Model

DataData Cook-TorranceCook-Torrance

He-TorranceHe-Torrance

ĎurikovičĎurikovič

ErshovErshov

AshikhminAshikhminInput BTDFInput BTDF

Measurable parametersMeasurable parameters

Paint namePaint name

ResultResult

Comercial databaseComercial database

Not measurable parameters

Not measurable parameters

Ershov - inverseErshov - inverse

return paint name closest to calculated parameters

compression

faster rendering

Conclusion

• my work describes 5 models of reflectance functions• gives standard function representations• summarizes their used parameters• discusses which parameters can be easily measured• compares available results and known difficulties• introduces to problems of car paint rendering• proposes a concept for black box model as a solution


Thank you for your attention !

Overview of Reflectance Models Focused on Car Paint Simulation Advisor: doc. RNDr. Roman...

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