Diffused Illumination

I've started taking a look at what would be necessary to start implementing support in touchlib for what I am hereby naming the 'diffused illumination' approach. Someone else proposed Rear Illuminated but it can also be front illuminated so we need a name that works for both. The picture is a test run doing a 'front illuminated' setup. I just pointed my screen towards the window and recorded a test movie. I've developed a simple algorithm that I think will work well for front and rear illuminated setups (front illuminated setups just need an extra step to invert the colors). Basically the algorithm is to blur the image then subtract the blurred image from the original. I believe this is how Photoshop's high pass filter works. I then also blur the image again to get rid of noise. What you are left with is the parts of the image that are sharp and in focus and the blurry parts are removed, which is exactly what we want.