This collaboration of two displays is very intruiging. When holding an transparant object like a piece of paper or glass, above the big screen, it shows a totally different image. Here's the trick:The system consist of a large flat screen and two monitors that are positioned underneath.
The screen is an LCD that can switch between opaque and transparent, alternating 60 times per second. The two projectors are both flickering at 30 times per second. One of the projectors is timed to shine up under the screen when it’s opaque, while the other is timed to shine through when the screen is transparent. Anything held above the screen will show what’s being projected by that second projector.
Gizmodo: The craziest thing about it is that the second projector can actually follow special objects, projecting the runner you see in the first video anywhere the panel goes, and in the appropriate proportion.