11 - Lighting

ucla | CS 174A | 2024-03-18 22:08

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Table of Contents

• Types of lighting
• Ambient Lighting
• Diffuse Lighting
• Specular Lighting
  • Calculating R vector
  • Blinn-Phong: Replacing RV with Halfway Vector
• Final Lighting
  • Incident Angle
  • Directional light sources
  • Attenuated Light source
  • Colored Light Sources
  • Fog: Atmospheric Attenuation and Blending
  • Misc Improvements
• Global Illumination

Types of lighting

• ambient - instead of checking the physical scattering, we assume each object has ambient lighting directly behind it that gives us a silhoutte
• diffuse - reveals shape of obj based on diffusivity of light across the surface of the object
• specular - shine, shows specualr highlights of the light soruces

  Ambient Lighting

• background light - estimates true scattering
• does NOT depend on position/direction, object, or eye

  Diffuse Lighting

• point source light
• lambertian (diffuse) reflection for dull matte surfaces -> looks equally bright from all directions
• reflect light equally in all directions
  • 
• Lambert’s law: light intensity is prop to direction
• N is the normal from/to the surface
• L is the light vector (surface to light source)
• $\theta$ is angle between N,L

  Specular Lighting

• shiny surfaces
• color of light matters (included in point light intensity) not color of object
• depends on position of light, object and eye
• R is the reflection vector from the surface
• V is the view/eye/cam vector from the surface
• $f_{att}$ is attenuation factor: see Final Lighting
• $\varphi$ is angle between R and V

Calculating R vector

$\overrightarrow{R}=2(\overrightarrow{N}\cdot \overrightarrow{L})\overrightarrow{N}-\overrightarrow{L}$

Blinn-Phong: Replacing RV with Halfway Vector

• halfway vector $\overrightarrow{H}$ is halfway b/w L and V = norm(L+V)
• replace $(R\cdot V{)}^n$ with $(H\cdot N{)}^n$
• s.t. $(H\cdot N{)}^n={\cos }^n\mathrm{\Psi }:\mathrm{\Psi }=\varphi /2$

  Final Lighting

  $I_{\lambda }=(k_{a\lambda }\ast I_{a\lambda })\ast O_{d\lambda }+(f_{att}\ast k_{d\lambda }\ast I_{p\lambda }\ast (N\cdot L))\ast O_{d\lambda }+(f_{att}\ast k_{s\lambda }\ast I_{d\lambda }\ast (R\cdot V{)}^n)$ where $\lambda \in R,G,B$

  Incident Angle

• angle is angle bw norm to surface and light source
• $\theta <90$ => some light based on angle
• $\theta =90$ => max light
• $\theta >90$ => self-occlusion, no light

  Directional light sources

• if light is far enough away
• L is the same (constant) for the entire scene for all objects
• N is the same for the entire polygon
• thus $N\cdot L$ is constant on the poly

  Attenuated Light source

• diffuse light reflected off object
• d is the distance of the light to the object

  Colored Light Sources

  OBJECT COLOR (not light color)

• object’s diffuse color $O_{d\lambda }\in O_{dR},O_{dG},O_{dB}$
• split into R,G,B components
• thus final term => (ambient + diffuse term) * $O_{d\lambda }$

  Fog: Atmospheric Attenuation and Blending

  

  Misc Improvements

  

Global Illumination

• based on physics light energy (radiosity)
•