Illumination Tech of CG.

Direct Illumination Problems and Advantages

Direct Illumination is a term that covers the principal lighting methods used by old school rendering engines such as 3D Studio and POV. A scene consists of two types of entity: Objects and Lights. Lights cast light onto Objects, unless there is another Object in the way, in which case a shadow is left behind.

Ray Tracing:
- Can render both mathematically described objects and polygons
- Allows you to do some cool volumetric effects
- Slow
- Very sharp shadows and reflections

Shadow Volumes:
- Can be modified to render soft shadows (very tricky)
- Tricky to implement
- Very sharp shadows
- Polygons only

Z-Buffer:
- Easy to implement
- Fast (real-time)
- Sharp shadows with aliasing problems


Global Illumination Problems and Advantages

Images produced by global illumination methods can look very convincing indeed; in a league of their own, leaving old skool renderers to churn out sad cartoons. But, and it's a big 'but': 'BUT!' they are slower. Just as once you may have left your ray tracer all day, and come back to be thrilled by the image it produced, you will be doing the same here.

Radiosity:
- Very realistic lighting for diffuse surfaces
- Conceptually simple and easy to implement
- Easy to optimise with 3D hardware
- Slow
- Does not handle point sources well - nor shiny surfaces
- Always over complicated and poorly explained in books

Monte Carlo Method:
- Very, very good results.
- Can simulate pretty well any optical phenomenon
- Slow
- Slightly difficult
- Requires some cleverness to optimise
- Always over complicated and poorly explained in books

Reference:http://freespace.virgin.net/hugo.elias/radiosity/radiosity.htm