Will visual light interfere with infrared light from laser?

Question

I want to make a "virtual keyboard" like the type you can buy from best buy, but instead of using a laser projection of the keyboard template I want to use a micro projector to project a more realistic version of the keyboard (and other screens). See this diagram:

When put your fingers in the infrared linear laser the camera detects the light being reflected off of them. Id replace the "keyboard pattern projector" with an actual projector (with some rearranging I'm sure). Would the be able to differentiate the visible light hitting your fingers (or even before it hits your fingers) and the laser light hitting your fingers? I'd think they'd operate on different wavelengths but my physics knowledge is ̶n̶o̶n̶e̶ very limited so I'm unsure.

Answer 1

It would be quite easy to do this with the right filter. A filter that only lets IR through is used in many applications (it's the "almost black" plastic window on the receiver of the remote for many appliances). This would significantly improve the ability to differentiate IR from the keyboard pattern. If you are using a color projector, you could use blue or green for the keyboard to further separate the two - in that case, you can see whether your color camera "sees" the keyboard colors in the green and blue channels on the camera, and subtract out some appropriate amount of signal.

Finally, you can use strobing: if you blink your IR laser (at about 15 Hz, so half the frame rate of the camera) you could look for the changing signal as being due to the laser. The eye won't notice this because it's insensitive to the IR, and it makes the image processing very simple - just subtract consecutive images from the video stream, and the difference is due to the IR laser.