alpha layer trigger

[Scott Hooson]

Does anyone know if it would be possible to have a graphic overlay (say a grid) over live video that would enable an event to be detected when some boundary was crossed. Possibly there could be some readily identified subject characteristic that can be thresholded, but it would be great if that could be flexibly defined. The event trigger could be sent to an external application to make a beep or flash a light or capture a freeze frame. I would like to use video from a DSLR if possible as input.
Many Thanks for thinking about this and responding!

[surfmonkee]

isadora, but its not cheap

http://www.troikatronix.com/isadora.html