With everything in place, I performed the first true test of the multi-touch surface, using the Touchlib library.

The camera was still extremely sensitive to visible light, so much so that the blobs were not being detected correctly and there was a lot of interference. The proper way to filter out the visible light spectrum would be to use an IR band-pass filter with the right wavelength for the LEDs (in our case, 880nm) so that only the LEDs’ light can reach the camera (and nothing else, even in the infrared range). Instead of buying a filter, I decided to use the lazy-man’s visible light filter: exposed negative film. I placed three exposed negatives on top of the camera lens and the blobs were instantly clearer and the software could detect blobs and movement extremely accurately.