CS348B Lecture 17 Pat Hanrahan, Spring 2005

Reflection Models

Previous lecture

Phong model

Microfacet models

Gaussian height field on surface

Self-shadowing

Torrance-Sparrow Model

Today

Multiple importance sampling

Anisotropic reflection models

Multiple Importance Sampling

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Multiple Importance Sampling

Reflection of a circular light source by a rough surface

Radius

Sh

inin

ess

Sampling the light source Sampling the BRDF

( ) ( )f x g x dx

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Multiple Importance Sampling

Two sampling techniques

Form weighted combination of samples

The balance heuristic

2, 2

2,2,

2 2,

~ ( )

( )

( )

i

ii

i

X p x

f XY

p X

1, 1

1,1,

1 1,

~ ( )

( )

( )

i

ii

i

X p x

f XY

p X

1 1, 2 2,i i iY wY w Y

1 1 2 21 2

( )( ) ( ) ( ) ( ) ( ) ( )

( ) ( )i

i

p xw x p x w x p x w x p x

p x p x

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Multiple Importance Sampling

Source: Veach and Guibas

Anisotropic Reflection Model

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Anisotropic Reflection

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Quarterhorse

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Reflection from a Cylinder

T

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Reflection from a Cylinder

T

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Reflection from a Cylinder

T

L

ˆˆ( )

NR L

N

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Reflection from a Cylinder

T

L

ˆˆ( )

NR L

N

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Reflection from a Cylinder

T

L

ˆˆ( )

NR L

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Anisotropic Reflection

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Shape of Anisotropic Highlights

From Lu, Koenderink, Kappers

Fibers tangent to the plane defined by the halfway vector reflect light

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Shape of Anisotropic Highlights

From Lu, Koenderink, Kappers

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Kajiya-Kay Model

Diffuse

Specular

2ˆ ˆsin 1L T L

cos cos cos sin sinss

E L E L E L

L

E

T

ˆˆ( )

NR L

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Herbert

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Fiber Model

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Fiber Model

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Fiber Model

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Caustics

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Hair Appearance

CS348B Lecture 17 Pat Hanrahan, Spring 2005

Hair Appearance

CS348B Lecture 17 Pat Hanrahan, Spring 2005

CS348B Lecture 17 Pat Hanrahan, Spring 2005