Advanced Illumination

Spring 1999

Computer Science and Electrical Engineering Department

University of Maryland, Baltimore County

**Illumination Review**

- ambient -- approximate global illumination effects.
- diffuse -- Lambert's Law -- absorbed and reradiated equally in all directions (depend on wavelength, independent of observer)
- specular -- reflects off surface => color of light in many cases is color of object.

**flux**- -- rate at which energy is emitted (Watts).
**solid angle**- -- angle at the apex of a cone. It is measured in terms of the area on a sphere intercepted by a cone whose apex is at the sphere`s center.
**steradian (sr)**- -- solid angle of a cone that intercepts an area equal
to square of the sphere's radius
*r*. - hemisphere has sr.
**Radiant intensity**- -- flux per unit solid angle in a given direction.
**Radiance**- -- radiant intensity per unit foreshortened surface area.
(W/sr*m
^{2}) **Foreshortened surface area**- - projected surface area -- projection of surface onto
the plane perpendicular to the direction of radiation. It equals to

where is the angle between radiation and surface normal. **Irradiance**- -- the incident flux per (unforeshortened) unit surface area.

**Irradiance of incidence light :** .
where
is incident radiance.

Bidirectional reflectivity :

Cook-Torrance use

* (N*L)

where

*D* is distribution function of microfacets orientations

*G* is geometrical attenuation factor -- masking
and shadowing effects of the microfacet on each other.

is the Fresnel term.

Blinn's model

- Phong's model

- Blinn

where and .

- T-Sparrow

- C-Torrance

where*m*is root mean square slope of microfacets (Beckman distribution).

where , is angle of incidence relative to , and n is index of refraction.

In another form

where and .

Formula:

where ,
and .

Also can do it as:

where Red(0) is color of material at normal incidence. Then,

Hall suggested a similar method.

Last modified: Wed Mar 10 17:07:01 EST 1999