Green screen alternative -- Rear projection of 3D image rendered in real time
Too interesting -- watch the video on the page:
"The concept is simple. There are four LED display walls, one behind the actor, two to either side, and one representing the sky. There is also lighting provided by Arri Skypanels. So far so simple.
What makes this all work is that the Unreal Engine 'virtual set' is displayed on the three LED panels, but the system also controls the Skypanel lighting as well. Camera movement is tracked in realtime, so that the viewpoint of the virtual set is moved according to its position. When you're sat on set it just looks like the virtual set is changing perspective. But look through the camera viewfinder and you discover that the set viewpoint is being moved with perfect positioning according to camera position. The result is that the background moves in perfect parallax."