Surfaces are illuminated by light whether by direct light from a light source or by reflected light from one or more surfaces in the environment. Smoke , fog or dust may inhibit the light. Different surfaces have a different reflectivity as some light is absorbed by the surface and some may pass through the surface. The reflectivity of a surface is often defined as its colour. The reflection of light energy in an environment causes “colour bleeding”, where a bright colour will “bleed”onto adjacent surfaces.
With Radiosity, computer image generation assumes surfaces are emitting and reflecting indirect uniform diffuse lighting over their whole area. It assumes all the energy is used in absorption and reflection and that it is viewpoint independent of the image. It also assumes that surfaces inter-reflect i.e. they both receive and send out light energy. To calculate radiosity, surfaces are broken down into patches. Once a solution has been calculated, the camera can move around anywhere with this solution. If however the light changes, a new solution has to be calculated. The Radiosity of a surface is the rate at which energy leaves the surface, including energy reflected from other surfaces.
Radiosity gives colour subtlety. Within 3Dmax there are working tools (e.g. exposure) to make a scene more realistic.
As seen fron the above images standard lighting, which is direct illumination, has no reflected light and gives hard , blocky images and dark shadows. It is however cheaper and faster to render so may be suitable for certain scenes.
Filed under: Radiosity and Ray Tracing
