Diffused Illumination vs FTIR

This post is just a quick recap for those that haven't been following all the discussions. What I am terming 'diffused illumination' is shining an infrared light source through the screen (either behind the screen with the camera and projector or behind the user as you might be able to do using daylight as your light source). The screen also acts as your diffuser which causes any objects behind it to appear blurry. Only objects very close to the screen can be resolved. Diffused illumination illuminates the whole hand and there are a couple different ways you can analyze the image - you can use some kind of shape based approach to pick out the fingers or try something like the approach illustrated in a past blog post. This is the technique employed by the CityWall and Microsoft's Surface. The advantage of the Diffused Illumination approach is that you can use things other than fingers such as pencils, brushes or pointers. The dryness of your fingers doesn't matter and dragging operations should work a lot better. Also it lends itself to using fiducial tags which are markers you can apply to objects that can be recognized by the system and tracked. This is how Microsoft's Surface can track cell phones, credit cards, juice cups, etc. Tags also lend themselves to board games with tangible peices. Diffused illumination may also be more tolerant to bright environments and is probably the only technique that can work in daylight. DI is also a lot easier to make - you can just buy an infrared light source. No need to solder LED's or calculate resistor values. I still need to do some more testing (I should be getting a new infrared light source later this week) so I will post how it works out.