CPSC 441: Computer Graphics Lighting

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CPSC 441 Computer GraphicsLighting

• Jinxiang Chai

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3D Rendering pipeline
Modeling transformation
Transform into 3D world system
Illuminate according to lighting and reflectance
lighting
Transform into 3D camera coordinate system
Viewing transformation
Transform into 2D camera system
Project transformation
Clip primitives outside cameras view
Clipping
Draw pixels (includes texturing, hidden surface,
etc.)
Scan conversion
Image
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3D Rendering pipeline
Modeling transformation
Transform into 3D world system
Illuminate according to lighting and reflectance
lighting
Transform into 3D camera coordinate system
Viewing transformation
Transform into 2D camera system
Project transformation
Clip primitives outside cameras view
Clipping
Draw pixels (includes texturing, hidden surface,
etc.)
Scan conversion
Image
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Outline

• Ambient, diffuse and specular light
• Light attenuation spot lights
• Readings HB 10-1,10-2,10-3

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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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Direct and Indirect Light
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Global Illumination II
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Global Illumination II
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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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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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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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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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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

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Types of Reflection Functions

• Ideal Specular
• Reflection Law
• Mirror
• Ideal Diffuse
• Lamberts Law
• Matte

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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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Materials
Plastic
Metal
Matte
From Apodaca and Gritz, Advanced RenderMan
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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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Materials
Plastic
Metal
Matte
From Apodaca and Gritz, Advanced RenderMan
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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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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

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

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Opengl Functions

• See section 10-20
• how to set up light sources (light source pos
• - light source position and type
• - light source colors
• - radial-intensity attenuation
• - spotlights
• how to specify global lighting parameters
• how to specify surface properties

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Next Lecture

• Shading
• Texture mapping others
• Readings HB 10-10, 10-17, 10-18