1. Overview of Reflectance Models Focused on Car Paint Simulation Advisor: doc. RNDr. Roman Ďurikovič, PhD. Róbert Smetana

2. Contents Goals of the Thesis Paint Composition BRDF Explained Reflectance Models Black Box Model Conclusion FMFI UK, June 2008Róbert Smetana2

3. 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 FMFI UK, June 2008Róbert Smetana3

4. Paint Composition why is car paint modelling difficult? multiple layers multiple types of flakes with different reflectance, absorption and scattering properties FMFI UK, June 2008Róbert Smetana4

5. Different Coatings FMFI UK, June 2008Róbert Smetana5 Blue pigment onlyMetallic flakesPearlescent flakes * Rendered by Ďurikovič et al. in paper [ĎÁ07]

6. 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) FMFI UK, June 2008Róbert Smetana6

7. Multiple Lobes macro-appearance attributes shade, glitter and gloss more precise when described by own lobe FMFI UK, June 2008Róbert Smetana7

8. 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 them FMFI UK, June 2008Róbert Smetana8

9. 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 FMFI UK, June 2008Róbert Smetana9

10. 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 FMFI UK, June 2008Róbert Smetana10

11. 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 FMFI UK, June 2008Róbert Smetana11

12. Black Box Model FMFI UK, June 2008Róbert Smetana12 Black Box Model Data Cook-Torrance He-Torrance Ďurikovič Ershov Ashikhmin Input BTDF Measurable parameters Paint name Result Comercial database Not measurable parameters Ershov - inverse return paint name closest to calculated parameters compression faster rendering

13. 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 FMFI UK, June 2008Róbert Smetana13

14. Thank you for your attention !