I went back to do some improvements in my radiosity solution. I added several bounces to the light and also translucency for some materials.
The following render shows the effects of the new algorithm:
This is the light-map generated by the radiosity solution for the same scene:
As you can see there is a lot of color bleeding from the tree leaves into the walls. The light in the tree crown actually comes from the other side, which is directly hit by sunlight.
Soon I will be posting more details about this method. It is a hybrid between GPU and CPU. It is not realtime. A scene 100 meters by 100 meters takes around four seconds in an ATI Radeon 4770, Intel Core 2 Quad CPU at 2.8 GHz.