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Reflection Models I

Reflection Models I. Today Types of reflection models The BRDF and reflectance The reflection equation Ideal reflection and refraction Fresnel effect Ideal diffuse Next lecture Glossy and specular reflection models Rough surfaces and microfacets Self-shadowing

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Reflection Models I

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  1. Reflection Models I • Today • Types of reflection models • The BRDF and reflectance • The reflection equation • Ideal reflection and refraction • Fresnel effect • Ideal diffuse • Next lecture • Glossy and specular reflection models • Rough surfaces and microfacets • Self-shadowing • Anisotropic reflection models University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  2. Reflection Models • Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency. • Properties • Spectra and Color [Moon Spectra] • Polarization • Directional distribution • Theories • Phenomenological • Physical University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  3. Types of Reflection Functions • Ideal Specular • Reflection Law • Mirror • Ideal Diffuse • Lambert’s Law • Matte • Specular • Glossy • Directional diffuse University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  4. Materials Plastic Metal Matte From Apodaca and Gritz, Advanced RenderMan University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  5. The Reflection Equation University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  6. The BRDF • Bidirectional Reflectance-Distribution Function University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  7. The BSSRDF • Bidirectional Surface Scattering Reflectance-Distribution Function Translucency University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  8. Gonioreflectometer University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  9. Properties of BRDF’s • 1. Linearity • 2. Reciprocity principle From Sillion, Arvo, Westin, Greenberg University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  10. Properties of BRDF’s • 3. Isotropic vs. anisotropic • 4. Energy conservation Reciprocity and isotropy University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  11. Energy Conservation University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  12. The Reflectance • Definition: Reflectance is ratio of reflected to incident power • Conservation of energy: 0 <r< 1 • 3 by 3 set of possibilities: • Units: r [dimensionless], fr [1/steradians] University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  13. Law of Reflection University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  14. Ideal Reflection (Mirror) University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  15. Snell’s Law University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  16. Total internal reflection: Law of Refraction University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  17. Optical Manhole Total internal reflection From Livingston and Lynch University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  18. Fresnel Reflectance Metal (Aluminum) Dielectric (N=1.5) Gold F(0)=0.82 Silver F(0)=0.95 Glass n=1.5 F(0)=0.04 Diamond n=2.4 F(0)=0.15 Schlick Approximation University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  19. Experiment • Reflections from a shiny floor From Lafortune, Foo, Torrance, Greenberg, SIGGRAPH 97 University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  20. Approximated Reflectance Cook-Torrance approximation Cook-Torrance Model for Metals Reflectance of Copper as a function of wavelength and angle of incidence Measured Reflectance Light spectra Copper spectra University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  21. Lambert’s Cosine Law Ideal Diffuse Reflection • Assume light is equally likely to be reflected in any output direction (independent of input direction). University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  22. “Diffuse” Reflection • Theoretical • Bouguer - Special micro-facet distribution • Seeliger - Subsurface reflection • Multiple surface or subsurface reflections • Experimental • Pressed magnesium oxide powder • Almost never valid at high angles of incidence • Paint manufactures attempt to create ideal diffuse University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  23. Phong Model R(E) E R(L) E N N L L Reciprocity: Distributed light source! University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  24. s Phong Model Diffuse Mirror University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

  25. Properties of the Phong Model • Energy normalize Phong Model University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell

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