reflect ance models

7/24/2019 Reflect Ance Models

1/15

Reflectance Models

CS 319

Advanced Topics in Computer Graphics

John C. Hart


2/15

ocal !llum. Conte"t

# Surface point $x% and normal $N%

# i&ht source $S' notL%

( )ector from xto li&ht *source+

( ,ir. incident radianceLi-L$S%

comesfrom$lie /ind direction%

# )ie/ vector $V%

( ,irection from xto *vie/er+

( Reflected radianceLr-L$V% dir.# Reflection vector $R%

R- 0$NS%N( S

# Half/a vector $H%

H- $V2S%44V2S44

N

SR

V

H

$R%

$S%

x

All vectors are unit len&th


3/15

Some Spec$tac%ular Hacs

# ,ecompose 5R,6diffuse2specular

Lr- $fd2fs$S')%%LiNS

# 7hon&8fs- ksma"$VR'%n $NS%

# 5linn8fs- ksma"$NH'%n

$NS%# 5linn n- :7hon& n# ;ot


4/15

Coo=Torrance

# 5ased on Torrance=Sparro/ model

# 7hsicall plausi


5/15

6resnel >ffect

# ? of li&ht reflected increases as *half/aincidence an&le+ hincreases

( ;ormalNof rou&h surface not /ell

defined' so needHinstead

( S and ) nearl constant across surface

( 6resnel effect independent of ;

( ;earl constant across surface

# Affects color of reflected li&ht

( ;ormal incidencesurface color

( Tan&ent incidenceli&ht color

# 7hoto&raphic tric8 place


6/15

6resnel Term

# 6resnel termFcontrols portion of li&htreflected v. portion refracted $1 (F%

# 7hsicall accurate 6resnel function

( 7arameteried


7/15

Rou&hness Term

# Statistical model of li&ht reflectance

# Rou&hness m- RMS of slope

# 5linnBs hac

Dm'c$N'H% - ce"p$(0 m0%

( An&le - cos=1$NH% E'0F( Ar


8/15

5linn v. 5ecman

5linn

5ecman

m- m-1 m-0S


9/15

Geometr Term

# Shado/in&

( !ncident li&ht does not reach material

Gs$N'S'V% - 0$NH%$NS%$SH%# Masin&

( Reflected li&ht does not reach vie/erGm$N'S'V% - 0$NH%$NV%$VH%

# Geometr term - shado/ A;, mas

G$N'S'V% - minGs$N'S'V%' Gm$N'S'V%' 1I

( Clamp to one to eep demoninators in chec

x

Gs Gm G

S


10/15

Coo=Torrance ,emo

m-

m-0$


11/15

Seeli&er Sin

# Model for diffuse reflectance from sin

# Softer appearance than am


12/15

Hair

# 6rom a@ia L a SNN

# Anisotropic

# Kses tan&ent vector T

# ,iffuse anisotropic

fd- sin$T'S%

# Specular anisotropic

fs- $$TS% $TV% 2 sin$T'S% sin$T'V%%n

T

SS

sin$A'B% - sOrt$1=$AB%0%

Chan&' Jin L

Pu' 01


13/15

Hair >"amples

diffuse

spec.' n-1

spec.' n-N

diff2spec


14/15

6ur

# Goldman S9

# Scatterin& of li&ht


15/15

6ur >"amples

scatterin&

opacit

fae fur

reflect ance models

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