05-07-2012, 11:12 AM
ILLUMINATION MODEL
ILLUMINATION MODEL.ppt (Size: 861 KB / Downloads: 41)
An illumination model represents the light reflected from the surfaces of the object, which may be exposed directly to a light source or which may get light from nearby illuminated objects.
The source may be the ambient light or background, the point source and the distributed light source.
Illumination Model
Ambient light
In a real scene, objects receive light scattered from the surroundings e.g. the walls of a room are visible.
The combination of light reflections from various surfaces in the surroundings yields a uniform illumination called the ambient light or background light , which has no spatial or directional characteristics.
Iambient =KaIa where Ia is the incident ambient light intensity and Ka is the ambient diffuse reflection constant (0<=ka<=1)
Each surface is illuminated with the constant intensity Ia which is independent of the viewing direction and spatial orientation.
The coefficient ka determines how much of the incident light is to be reflected and how much absorbed by the surface.
Diffuse Reflection
Now consider illumination an object by a point source
When light strikes a surface, most of it is scattered equally in all directions . When light penetrates below the surface of an object, gets absorbed and then reemits equally in all directions. This is called Diffuse reflection.
The amount of diffuse reflection from a surface is primarily determined by the roughness or texture of the surface.
Dull, matte surfaces , such as chalk , exhibit diffuse reflection , also known as Lambertian reflection.
These surfaces appear equally bright from all viewing angles because they reflect light with equal intensity in all directions.