Rendering

 Radiosity is a global illumination algorithm which is used in 3D computer grpahics rendering.

This simulates the way light appears in the environment giving it a more realistic feel.

 

In the first image this shows what the lighting would look like in a 3D environment without the radiosity. As you can see, the lighting is very blocky and doesn’t look realistic.

In the second image they have used radiosity. As you can see there is a big improvement in the realism of the lighting and shows the shadows to be much softer like in real life.

The problems with radiosity is that it doesn’t work so well with glossy looking reflections and can’t handle sudden changes in visibilty.

Renderers will normally not add in the radiosity till the very last stage as it makes renderin time much longer.

Local Illumination

This is like an advance 3d environment calculator which will calculate what things should look like realistically, for example if  a usrface should be shiny this will calculate it and make it look shiny.

Ray-Tracing

Ray-tracing is a type of global illumination like radosity.

when light rays hit an object, one of three different things can happen, these are absorption, reflection and refraction. In 3D applications Ray-Tracing creates this illusion.

Basically it traces rays (hence the name ray-tracing) from the camera back thouugh the image plane into the scene.