Illumination Model Wireframe rendering simple, ambiguous Color - - PowerPoint PPT Presentation

Illumination Model

Wireframe rendering simple, ambiguous Color filling flat without any

3D information Requires modeling interaction of light with the object/surface to have a different color (shade) in 3D

Illumination Model

Light on a surface is

• Absorbed
• Reflected
• Transmitted

The amount reflected determines the color and brightness of the object light material (surface) interaction

Illumination Model

The reflected light is scattered depending upon the surface properties and incident light Ambient light comes from all directions, is scattered in all directions Diffuse light comes from one direction and is scattered in all directions Specular light comes from one direction and is scattered in preferred direction

Illumination Model

Diffuse Reflection

N L

θ

L: Light vector N: Normal θ: Angle between L and n Lambert’s Law

) ( cos N L I k I θ I k I θ cos α I

l d d l d d diffuse

• =

=

kd diffuse reflection coefficient

Illumination Model

Diffuse Reflection

Illumination Model

Diffuse Reflection

Illumination Model

Diffuse Reflection

Amount of light reflected depends on the direction to the light source and not on the direction to the viewer Viewer independent Distance from light source q can also be incorporated

) ( ) (

2

N L I cq bq a k N L I k I

l d l d d

• +

+ =

• =

Illumination Model

• Highlights / Shininess
• Viewing Direction

Specular Reflection

Illumination Model

L: Light vector N: Normal θ: Angle between L and N α: Angle between R and V

N L

θ θ

R V

α

Specular Reflection

n l s s n l s s

V R I k I α I k I ) ( cos

• =

=

ks specular reflection coefficient n specular reflection exponent

Illumination Model

n=1 5 10

large n: metals small n: paper Specular Reflection

Illumination Model

Specular Reflection

Example

Illumination Model

Light from distributed light sources (and surroundings) Also approximates effects of diffusely reflected light from outer bodies / objects.

Ambient Reflection

a a ambient

I k I =

ka ambient reflection coefficient Ia ambient incident light

Illumination Model

Phong Illumination Model

∑

=

• +
• +

=

• +
• +

= + + = + + =

m i n i i s i i d a a n l s l d a a n l s l d a a total

V R I k N L I k I k V R I k N L I k I k α I k θ I k I k reflection specular reflection diffuse reflection ambient I

1

) ( ) ( ) ( ) ( cos cos

Illumination Model

Phong Illumination Model

Local computation for obtaining color (intensity) at a point

• f the surface

Basic inputs are light(s), material properties

Illumination Model

Reflection Vector

N L R

θr θi

L N R

• L

N N L ) ( 2

• L

N N L R −

• =

) ( 2

Illumination Model

Half Way Vector

N L H V

Instead of R•V can use N •H H = L +V L +V

R

Illumination Model

Normal Vector Plane

= + + + d cz by ax

n p0 p

) (

0 =

−

• p

p n

Normalize c b a n ] [ =

Illumination Model

Normal Vector Plane

Normalize v v v v n ) ( ) (

1 2 1 3

− × − =

v1 v2 v3

Illumination Model

Normal Vector Sphere Implicit Equation

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ∂ ∂ ∂ ∂ ∂ ∂ = = − + + = z f y f x f n z y x z y x f , , 1 ) , , (

2 2 2

Illumination Model

Normal Vector Parametric Surface ) , ( ) , ( ) , ( ) , ( ) , (

, , , ,

v u b v v u b u v u b v v u b u v u n

n m n m n m n m

∂ ∂ × ∂ ∂ ∂ ∂ × ∂ ∂ = u ∂ ∂ v ∂ ∂ n

Illumination Model

Light Sources

Point light source Given by a point Light emitted in all directions Direction light source Given by a vector Spotlight light Given by a cone

Illumination Model