Light
Tom Kelliher, CS 320
Apr. 8, 2005
Read Chapter 6.
RoomView lab.
- Real world lighting.
- A lighting model.
- Types of shading.
- The Phong reflection model.
Discussion of next project.
- Viewer, lights, objects.
- Light properties?
- Material properties: Translucence, reflectance (specularity),
scattering (diffusion). Examples? Color of an object.
- How do lights and materials interact?
- The rendering equation. Calculation for each point in a scene.
- Need a balance between accuracy and efficiency.
- Local vs. global lighting. The graphics pipeline.
- General illumination function for a light source:
.
- Types of modeled light sources:
- Ambient light
- Point sources
- Spotlights
- Distant light sources
- Illumination function is a continuous function of wavelength.
- Complex computation, vision model.
- Luminance function:
- Uniform light --- ``background'' light.
- Model:
- Emits light equally in all directions.
- Assume point source at . Color vector:
- Illumination at due to ? Depends upon square of
distance:
- High contrast harshness due to shadow effects: umbra, penumbra.
- In practice, replace inverse square term with
where d is the distance and a, b, and c are constants chosen to
soften.
- Simple spotlight: point source with light emitted only through narrow
range of angles.
- Consider the source at to be restricted by the cone
described by and .
- For accuracy, distribution within the cone is modeled by .
- Re-calculating the -- vector.
- If the distance is ``large'' how much does the vector change?
- Replace source location with source direction:
- Near source:
(a point)
- Far source:
(a vector)
- Flat shading: each point on a polygon assigned same color.
- Gouraud (smooth) shading: assign colors individually to vertices,
interpolate.
- Consider an object point, and a light source .
- Important vectors:
- l: vector to light source.
- n: surface normal.
- v: vector to COP.
- r: reflection vector.
- The light from source to object can be described by:
(theoretically wrong but, in practice, right)
- Using material properties, distance from viewer, orientation of
surface and direction of source a reflection matrix can be constructed:
- (Simplified) Illumination at :
A global ambient term may be ``thrown'' in.
Thomas P. Kelliher
Thu Apr 7 11:09:41 EDT 2005
Tom Kelliher