More Light on Light
Tom Kelliher, CS 320
Apr. 22, 2013
Read 5.7-5.9.
Introduction to light.
- Derivation of Phong lighting model.
- Computing normal vectors.
Incremental final project.
- Consider an object point, and a light source .
- Important vectors:
- : vector to light source.
- : surface normal.
- : vector to COP.
- : reflection vector.
- The light from source to object can be described by:
(theoretically wrong but, in practice, right)
- Using material properties, distance from source, orientation of
surface and direction of source a reflection matrix can be constructed:
- (Simplified) Illumination at :
A global ambient term may be ``thrown'' in.
Same at each point on a surface:
Repeat for each color.
- Diffuse surface brightest at noon, dimmest at dawn, dusk.
- Lambert's law: we see only the vertical component of light:
- If and are normalized:
So:
- Specular reflection produces highlights.
- The smoother the surface (higher shininess) the narrower the range
of reflection angles.
- Reflectivity proportional to angle between viewer () and
perfect reflection ():
where is the shininess term:
- for objects with broad highlights.
- 100 to 500 for most metallic objects.
- Assuming normalized vectors:
Computed for each light source and each color:
- Outward facing normal must be specified for each vertex.
- Analytic surfaces: cross product of partial differentials
- Polygonal surfaces:
- Points of continuity.
- Points of discontinuity.
Thomas P. Kelliher
2013-04-21
Tom Kelliher