I applied a patent to Japan patent Office a few weeks ago. It is about sensing of finger gestures on some object surface (palm, desk, wall, bag, and any). I may apply PCT patent too.
The background motivation:
I have a suspect about gesture in the air. It is socially strange if you do such gestures in air in front of the other persons. It is because human kind has not used such gestures in its long history (except pointing by index finger). It lacks the reality of human natural behaviors. Moreover it does not keep privacy. And, from the design point of view, a gesture decoding has the complexity to search in the 3D space.
On the other hand, human kind has a long history of use of finger gesture on surface of some objects – papers, and naturally uses it. Moreover it can hide gesture from someone else. And a gesture decoding in the 2D space is simpler.