Lighting Content Factors



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tarix01.02.2018
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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



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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