Hi, I can only second what damien already said. you have to use an infrared light source. there are cheap infrared LED arrays that you can use. the camera setting that reads only the infrared light is called nightshot and you will get best results if you find a camera that has a switch like that. then you will get a b/w image, and since the projector does not cast infrared light, the projection image is invisible to the nightshot camera. marius.

Damian Stewart wrote:

Joseph Barrows wrote:

...

hi all, I would like some advice, i wish to track objects using a video camera and pd/gem (easy enough) but I would then like to project video into that same space, but avoid it interfering with the video object processing. is there some simple way to do: (live video) - (gem generated video) = video used for blob tracking ? (if there is some way to offload it to the gpu that would be good too)

use infrared lighting and cameras. (this also gives you the advantage that you can flood the projection area with invisible infrared light, which is great for tracking, while keeping the 'real' visible lighting to a minimum).

most security cameras based on CCDs already detect infrared. if you put a piece of exposed and developed camera print film (just ordinary film) between the lens and the CCD, this blocks visible but allows infrared light through. to make a super cheap infrared light from a theatre light or any incandescent light, put 2-3 layers of Congo Blue theatre lighting gel and one layer of Primary Red gel in front of the light. be careful, it gets very hot.

d