13-08-2012, 02:42 PM
CAP4730: Computational Structures in Computer Graphics
lighting_and_shading.ppt (Size: 820.5 KB / Downloads: 70)
Lighting
Two components:
Lighting Model or Shading Model - how we calculate the intensity at a point on the surface
Surface Rendering Method - How we calculate the intensity at each pixel
The lighting problem…
What are we trying to solve?
Global illumination – the transport of light within a scene.
What factors play a part in how an object is “lit”?
Let’s examine different items here…
Light Source Properties
Color
We usually assume the light has one wavelength
Shape
point light source - approximate the light source as a 3D point in space. Light rays emanate in all directions.
good for small light sources (compared to the scene)
far away light sources
Light Source Direction
In computer graphics, we usually treat lights as rays emanating from a source. The direction of these rays can either be:
Omni-directional (point light source)
Directional (spotlights)
Diffuse Term
To determine how much of a diffuse contribution a light supplies to the surface, we need the surface normal and the direction on the incoming ray
What is the angle between these two vectors?
Idiffuse = kdIlightcos = kdIlight(N . L)
Ilight = diffuse (intensity) of light
kd [0..1] = surface diffuse reflectivity
What CS are L and N in?
How expensive is it?