More information on the VFX in Angels & Demons, this time from VFXWorld. They cover the huge photo montages that were required, but then get into some of the modeling and rendering tricks used in some of the huge crowd scenes.
It was decided, therefore, to use RenderMan‘s point cloud baking tools to bake all the illumination into a series of point clouds. Using additional proprietary tools, the team was able to combine all the point clouds for the different groups of lights together, so that they had one point cloud for each region. By splitting up the lighting in this way, they were able to use memory intensive techniques like ray tracing to get the best possible quality in the lighting.
They were also able to use the tools that Pixar had added to calculate ambient occlusion and color bleeding from the point clouds. These were then combined together in the renders, but could be overridden if the lighting had to change. Baking the lighting in meant that the lighting artists could build their scene, hit render, and immediately have a decent starting point for realistic lighting.
via VFXWorld.
