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BASIC ILLUMINATIONA basic illumination is obtained by an ambient light 

which determines the brightness of the scene. It isuniform for all objects, independent of the viewing

point and direction. The amount of the reflected light

(diffuse reflection) depends however on the surface

optical properties.

ambient

If the ambient light of the scene is and is surfce

ambient reflection parameter, the contribution to

surface reflection at any point is .

a a

a a

 I k 

 I k I =

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DIFFUSE REFLECTION

The amount of incident light depends on the

orientation of the surface relative to the

light source direction.

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θ    θ 

Incident

light

N

l  I 

,diffuse

For a light source and surface reflection parameter 

 (independent of ambient relection parameter ),

the diffused reflection is cos .

l 

d a

l d l 

 I 

k k 

 I k I    θ =

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( )

source surface

source surface

,diffuse

The unit direction vector of a nearly point light

source incident with a surface is given by

. The difused reflection is| |

, 0

0.0,

l 

d l 

l 

 I 

k I  I 

−=

−

× × >=

×

L

P PL

P P

N L N L

N

.

0

≤   L

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( )diffuse

ombining ambient and a single point source, the total

diffuse reflection is

, 0

., 0

a a d l  

a a

k I k I   I 

k I 

+ × × >

=  × ≤

N L N L

N L

more

diffuse

  m  o  r  e

  a  m   b   i  e  n   t

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SPECULAR REFLECTION AND

THE PHONG MODEL

  The bright spot (specular reflection) shown

on a shiny surfaces is the outcome of totalreflection of the incident light in a

concentrated region around the specular-reflection angle

  normalN

  viewingV

  lightL   reflectionR θ    θ 

φ 

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  A shiny surface has a narrow specular

reflection range.

  A dull (rough) surface has a wide specular

reflection range

  normalN

  viewingV

  lightL   reflectionR θ    θ 

φ 

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