Infrared reflection and absorption

    Nov 13 2012 | 2:57 pm
    Howdy folks!
    Not strictly a jitter question, but there has been a lot of infrared motion tracking talk on this forum in the past, so I'm hoping someone here might have an answer to this question.
    Short form question - what clothing/materials/fabrics would you recommend for a dancer that can either absorb most IR light or are highly, highly IR reflective?
    Long form question:
    I already have my tech setup in place - infrared emitter, near-infrared b&w ccd camera + IR filter to block out visible spectrum light. I'm using a basic differencing technique to determine where my dancer is in front of the camera. I send an image of my empty but lit stage into the right inlet of an absdiff operator and my live camera feed into the left inlet. I pass that through a > operator which gets rid of everything below a certain threshold and bumps everything above that threshold up to 1. Walaa, I get a brilliant white mask of where my dancer is, even in the dark. A little corner pinning and NURBS adjusting later and I'm projecting straight back onto my dancer.
    The problem I'm having is getting my dancer to have a higher Infrared reflectivity than her backdrop. It's easy when she's doing floor work because the painted wood floor absorbs most IR light, so she sticks out like a sore thumb in comparison to it which works great for my threshold technique. However, we'd also like to have the flexibility to have her in front of a projection screen, for either front or rear projection (we have both kinds of screens). The problem with this is that a projection screen is designed to be highly reflective, and it seems to reflect IR light just as well as visible light. If I have a highly IR reflective backdrop, in order to pick out my dancer, I need something that either reflects far more IR light, or mostly absorbs IR light.
    I've been doing a lot of google research on this, yet am having difficulty finding any concrete answers. Any input would be much appreciated!
    Thanks, Zach