Dr. Scott Schaefer

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Lighting

• Dr. Scott Schaefer

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Lighting/Illumination

• Color is a function of how light reflects from
  surfaces to the eye
• Global illumination accounts for light from all
  sources as it is transmitted throughout the
  environment
• Local illumination only accounts for light that
  directly hits a surface and is transmitted to the
  eye

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Global Illumination
Image taken from http//graphics.ucsd.edu/henrik/
images/cbox.html
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Reflection Models

• Definition Reflection is the process by which
  light incident on a surface interacts with the
  surface such that it leaves on the incident side
  without change in frequency.

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Types of Reflection Functions

• Ideal Specular
• Reflection Law
• Mirror
• Ideal Diffuse
• Lamberts Law
• Matte
• Specular
• Glossy
• Directional diffuse

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Illumination Model

• Ambient Light
• Uniform light caused by secondary reflections
• Diffuse Light
• Light scattered equally in all directions
• Specular Light
• Highlights on shiny surfaces

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Ambient Light

• A intensity of ambient light
• ka ambient reflection coefficient
• Really 3 equations! (Red, Green, Blue)
• Accounts for indirect illumination
• Determines color of shadows

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Total Illumination
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Diffuse Light

• Assumes that light is reflected equally in all
  directions
• Handles both local and infinite light sources
• Infinite distance L doesnt change
• Finite distance must calculate L for each point
  on surface

Surface
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Diffuse Light

• C intensity of point light source
• kd diffuse reflection coefficient
• angle between normal and direction to light

Surface
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Lamberts Law
Beam of Light
Surface
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Lamberts Law
Beam of Light
Surface
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Lamberts Law
Beam of Light
Surface
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Total Illumination
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Total Illumination
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Specular Light

• Perfect, mirror-like reflection of light from
  surface
• Forms highlights on shiny objects (metal, plastic)

Surface
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Specular Light

• C intensity of point light source
• ks specular reflection coefficient
• angle between reflected vector (R) and eye
  (E)
• n specular coefficient

Surface
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Finding the Reflected Vector
Surface
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Finding the Reflected Vector
Surface
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Finding the Reflected Vector
Surface
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Finding the Reflected Vector
Surface
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Finding the Reflected Vector
Surface
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Total Illumination
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Total Illumination
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Total Illumination
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Total Illumination
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Multiple Light Sources

• Only one ambient term no matter how many lights
• Light is additive add contribution of multiple
  lights (diffuse/specular components)

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Total Illumination
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Total Illumination
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Attenuation

• Decrease intensity with distance from light
• d distance to light
• r radius of attenuation for light

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Attenuation
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Attenuation
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Spot Lights

• Eliminate light contribution outside of a cone

Surface
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Spot Lights

• Eliminate light contribution outside of a cone

Surface
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Attenuation
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Spot Lights
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Spot Lights
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Implementation Considerations
Surface
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Implementation Considerations

• Two options
• 2-sided
• 1-sided

Surface
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Implementation Considerations

• Typically choose
• Clamp each color component to 0,1