Lighting Content Factors
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01.02.2018
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Lighting
Content
Factors
Reflection
Ambient Light
Diffuse Light
Specular Light
Illumination model
Factors
of illumination
We perceive images made by light
The light we see on a point depends on:
the light that arrives from the light source
the orientation of the point
the
features of the material
the light that arrives from other points
the position of the observer
Reflection of the light
The light can be reflected:
perfect
specular
reflection
imperfect specular reflection
diffuse
Illumination model
The reflected light of a surface is defined by:
Ambient light + Diffuse reflection + Specular reflection
I = kaIa + kdId + ksIs
Ambient light
kaIa
Ia is the ambient light of the scene
ka
is a property of the material
It is a simplification of the global illumination model
It substitutes the lights that doesn’t arrive directly from the source lights
Ambient light - image
Diffuse reflection
Lambert’s cosin Law
kdId = kd Ip cos = = kd Ip (n • l)
Ip is the light from a point source light
kd is a property of the material
It
is independent of the observer
It is the main component of the object’s color
Diffuse reflection - image
Specular reflection
The perfect specular reflection only produces reflection on a point
The imperfect specular
reflection is used in CG
The intensity decreases when we move away from the reflected ray direction
Fresnel Law: coss
It produces the shine of the objects
Specular reflection - calculation
ksIs = ks Ip coss = = ks Ip (r • v) s
Ip is the
light of a point light source
ks is a property of the material
s defines the diffusion, it is the specular parameter
Reflected vector
Calculation
of the reflected vector r
r = r1 + r2 [1]
- r1 = l + (-r2) => r1 = - l + r2 [2]
Replace in [1]:
r = - l + r2 + r2 = 2r2 - l [3]
r2 = (n • l) n [4]
Replace in [4]: r = 2 (n • l) n - l [5]
Specular reflection - image
Illumination Model
The light reflected by a surface:
Ambient light + Diffuse reflection + Specular reflection
I = kaIa + kd Ip (n • l) + ks Ip (r • v) s
Render
Gouraud render
Phong render
Global illumination Model
ray tracing
radiosity
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