Radiosity normal map
Lighting can be baked as a set of three light maps, storing the lighting vectors instead of just the brightness/color. This allows the surface normal maps to receive directional lighting so the bumps/recesses are lit more accurately by the baked lighting information.
Valve used this method extensively in Half-Life 2, which they called "Radiosity Normal Mapping" in their GDC 2004 paper Half-Life®2 / Valve Source™ Shading.
A further optimization of this technique was used by Insomniac Games for their game Resistance: Fall of Man. The directions of the light rays were combined into a single RGB bitmap, using a kind of normal map, where each color channel was used to store one of the three directional components.
All three RGB channels are used to store the light vectors, so the light maps could not also store the colors of the lights. Apparently they used vertex color to store the light colors.
- See the Polycount thread How to ? Directional lightmaps with 3dsMax/Vray.
- More reading at Jeffrey DeCew's site.
- For info about traditional light mapping see Light map.