Pasky’s Log

I spent large part of the weekend resurrecting my multitouch setup attempts again. I’m trying to use rear diffused illumination, but without much success yet. I have purchased two 1×1 meter 5mm thick plexiglass squares, but they are too impractical for the prototype yet, so I’m just using an A3-sized piece of glass with tracing paper underneath.

My elite IR light source:

Yesterday, I’ve used a setup with projector, camera and IR light source horizontally shining into a mirror reflecting everything at the surface. However, due to short cables ;-) this wasn’t very practical and everything had to be much too far from the mirror, plus there were some (although not so bad) double-reflections. So today I’ve rearranged the setup to a much simpler vertical one.

At the bottom is an Acer 1024×768 DLP projector, then on the white box is my IR light source illuminating the surface from an angle, then on the chair is sticked (literally) an IR webcam taking in a subset of the surface – a piece of glass with tracing paper sticked to the bottom side.

Unfortunately, so far I’m unable to get reasonably even IR illumination; it seems six leds are way too few, and the light is not diffused enough. I need to get multiple IR sources, and some translucent surface to diffuse the light a bit. Another problem is that the projector also shows the image in the IR spectrum, thus it somewhat interferes with the reflections; however, having strong enough IR light source should marginalize that problem.

The last problem is that my webcam is too crappy, on Linux it gives me only one to two FPS on 320×240. I’m planning to buy the absurdly cheap MSI StarCam Mini+ which should give me 30fps on 640×480 and has already night vision support so it should be enough to block visible light; I’m not feeling yet like shelling out huge money for Xbox or PS3 webcam.

Now I mainly wish I knew where to buy IR light sources in Prague…