Using Pure Data and home-made openCV externals , It detects squares.
The position and size of squares are mapped to loopplayers playing an audiosample at various positions and speeds.
When the square contains a red dot, it allows real-time recording from audio-input (here : a prepared piano) to the corresponding position in the sample.
The complete improvisation is viewable here .
Here another exploration of opencv features.
Using convexhull and convexitydefects fonctions
(Oranges are from Sicilia)