Air Guitar prototype

December 2010

In 2007 I attempted to make a simple Air Guitar prototype using a stereo camera (watch video). Unfortunately it didn’t work very well. You had to stand very still and the depth image wasn’t as clean as I would like.

Now that the much anticipated Xbox Kinect camera was out and opening up by the way, I wanted to port this demo to explore what the potential of interactive music games could be in the future & also just to experiment with the Kinect. 

How it works
First it thresholds the scene to find a person, then uses a histogram to get the most likely depth of a person in the scene. Then any pixels closer than the person to the camera are possible hands. It also uses contour extremity finding on the person blob to look for hands in situations where your hand is at the same depth as your body. It only works if you are facing the camera front on. Then it uses one hand as the neck of the guitar, drawing a virtual line from the neck through the person centroid to create the guitar line. The other hand is tracked to see if it passes through this line, strumming the guitar. The neck hand position controls the chord.

Technical Details
Written in c++ using openFrameworks and openCV for image processing. Thank you to the openframeworks and openkinect communities for enabling this to happen. A big thank you to Microsoft for bringing this technology to the mass market.

Limitations
My hand tracking is a simple first attempt, it's quite inaccurate and a bit flaky. You also have to face the camera in quite a specific way. With Xbox Kinect games, they have full skeletal tracking. Now with OpenNI, us homebrew developers can also play with these ideas. With full 3d skeletal tracking this would be 100% better. Also in terms of sound it is very simple chords, and of course is no replacement for a real guitar, but this is more like Guitar Hero / Rock Band playing than accuracy.