Next: Radiosity-based Global Illumination
Up: Advanced Lighting
Previous: Phong Reflection Model
- Point Light Sources:
- Point light sources have a position and
- Light energy is radiated equally in all directions
- Distance Attenuation:
- Physically, need attenuation since
light energy spreads out spherically.
- This is too harsh; point light sources
are rare in the real world.
- Use modified attenuation factor:
- This simulates the attenuation of an
area light source.
- Only use attenuation from light source to surface,
not from surface to pixel.
- Pixel is area, not point, so
foreshortening cancels attenuation.
- Ambient Lighting:
- True global illumination difficult and expensive to
- Often use constant low level lighting everywhere to
fake global illumination: .
- Each surface may reflect ``ambient'' lighting differently:
- Usually, .
- Lambertian Lighting:
at point x with point light sources at points
- Specular Lighting Similarly
- For example
- Sometimes we see the Phong model stated with
the half-vector :
- Angle between n and h is twice that between
r and v if coplanar
- Not exactly the equivalent of using reflection vector r
- Avoids recomputation of v
- Better approximations can be made to surface materials if we allow
multiple Phong lobes (SIGGRAPH 97)
CS488/688: Introduction to Interactive Computer Graphics
University of Waterloo
Computer Graphics Lab