dyeSight $2 Multi-Touch Pad

I guess most of the people reading this will have seen some of the multi-touch demos by Jeff Han, Apple and Tactiva. I wanted to play around with some ideas that required a multi-touch pad, but there aren't any devices available (Tactiva aren't shipping...)

Long story short, I made a simple one from a plastic bag, some dye and a camera:

The main idea is that you threshold the image into three areas: background (light blue), fingers (dark blue; these are shown as an overlay on-screen) and pressure points (not blue).

I used a bag of dye for now, since that was easy to make. It might be feasible to tape LEDs to the edges of the table, and use FTIR-like scattering; I'd like to try that later. Actually, if you have one of those cheesy engraved-perspex-plate-with-blue-LEDs-in-the-base things lying around, you might be able to use that.

Large areas of non-blue are interpreted as fingers. There is a mouse mode, where every touch immediately moves the mouse to that point, and a multi-touch mode which sends an NSNotification with a list of points for each frame. These will of course only be understood by programs that understand this protocol -- of which there currently exist only one (the rotozoomer at the end).

The on-screen display is just a regular transparent OSX window. The background pixels are 100% transparent (alpha=0), and the hands show up as black with alpha 0.1 or so.

The music is Sahara 7 by Shadow of the Beat, used with permission.