By now, we are all familiar with using ray tracing to find implicit surfaces, yet that is clearly not enough for us to render a surface.  For that we need to know what the color the object is, and how well it is lit.  If we wanted to be realistic, we’d also need to know the color of the incident light, as well as the properties of the surface.

In traditional ray tracing rendering, one casts a ray until it hits a surface, which can then casts additional rays to determine how much illumination that surface is receiving.  A good ray tracer can even account for reflections, refractions and shadows by being clever in what the program does after intersecting a surface.

There are a number of lighting methods out there, many of which use ray tracing.  Radiosity is a global illumination algorithm that treats all surfaces as light sources, on the ground that that’s basically what we see: light reflected from surfaces.  In Hugo Elias’s clever description of the algorithm, he examines the rational behind it in a brief interview with a piece of paint.

Mr. Elias does a wonderful job explaining various ins and outs of the methods using simple language that all of us will have no trouble understanding.  His presentation even goes so far as to be interesting, and funny at times.  Even if you don’t wish to know about lighting in 3D graphics, you can enjoy this article.

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

Mr. Elias has posted a number of other articles explaining a variety of graphic issues, which will be a good resource for anyone hoping to go into the graphics end of scientific computing.

http://freespace.virgin.net/hugo.elias/