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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
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

reflection models
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

types of reflection functions
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

materials
Materials

Plastic

Metal

Matte

From Apodaca and Gritz, Advanced RenderMan

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

the reflection equation
The Reflection Equation

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

the brdf
The BRDF
  • Bidirectional Reflectance-Distribution Function

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

the bssrdf
The BSSRDF
  • Bidirectional Surface Scattering Reflectance-Distribution Function

Translucency

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

gonioreflectometer
Gonioreflectometer

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

properties of brdf s
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

properties of brdf s10
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

energy conservation
Energy Conservation

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

the reflectance
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

law of reflection
Law of Reflection

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

ideal reflection mirror
Ideal Reflection (Mirror)

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

snell s law
Snell’s Law

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

law of refraction

Total internal reflection:

Law of Refraction

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

optical manhole
Optical Manhole

Total internal reflection

From Livingston and Lynch

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

fresnel reflectance
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

experiment
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

cook torrance model for metals

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

ideal diffuse reflection

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

diffuse reflection
“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

phong model
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

phong model24

s

Phong Model

Diffuse

Mirror

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

properties of the phong model
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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