An approach of simulating color transport in Maya in few steps without any extra light source...



Well, to begin I'd say that this tutorial is a global method to fake 'easily' and quickly radiosity in Maya. I know there's many different ways to achieve the same effect.

You may want to see this as a guideline more than a 'must-be-done-this-way' thing.

So, here is the workflow to simulate radiosity in Maya and other 3d packages (as a general workflow)

I've taken the Cornell box as example. No big deal for the model and the texture, simple materials with colors.

For the lighting, I first have worked with an area light (which is obviously the better light source in this case for illumination).
But as long as I worked on it, I noticed the shadows were too strong (to me). So finally I used a spotLight which is better for the shadows. If you tweak a bit the parameters, you can get an area light type of illumination with a spot.

A little technical spec seen by the artist I am. Color transport or reflected light 'technically' is 'globally' a ray that hits a surface, bounce on it according it's normal, and hits another surface, and so on...

Regarding radiosity package such as BMRT, color diffusion is given by the diffuse attribute of a material (Kd). The higher this attribute is, the more light will be emitted by the surface and then a close object object from a high diffuse material will receive more refected light than one with a low Kd.

In our case, the main trick is to see which object is supposed to receive color from another one.

The first thing is forget about radiosity. Make your shading and lighting 'as usual'. Once this is done, you have to calculate some passes of reflexions.
In this tutorial, I have rendered 3 different passes (One for the sphere and cube, one for the background wall (blue) and one for the roof and ground).

In each cases, I have applied a simple black blinn (with eccentricity set to 0, a white spec color, and fully reflective) and a 3d bump with a granite texture to the objects supposed to receive color.

Here are the images I used to generate the reflected color maps.


Sphere and cube pass...
Note the very noisy bump to catch colors from everywhere as the normal is perturbated.


The floor and roof pass...
Note that the sphere and the cube are only visible in reflection.


And the background wall.