This weekend, at Balticon (the Baltimore Science Fiction Convention) I got to play a bit with an infrared-sensing webcam. These turn out not to be very difficult to construct, because CCDs are sensitive well into the IR range. The normal filter blocks IR but passes visible light; by replacing it with fully exposed film stock, which is opaque to visible light but transparent to IR, you get infrared imaging.
The output was rendered live on a laptop as a mostly black-and-white image with occasional pale pseudocolors. The camera-builder explained that under daylight or artificial-light conditions, most of what you see is actually reflected rather than emitted IR; these light sources emit plenty of heat. (Someone demonstrated by pointing an IR remote control at the webcam that you can in fact see emitted IR. Hold that thought, it will be important when we reach our punchline.)
In fact, he claimed that human retinas have some sensitivity to IR that is normally swamped by the response to visible light; with the same film-stock trick done on a pair of welding goggles (he claimed) you can go outside on a bright sunny day and see in infrared without electronic amplification or frequency-shifting.
It’s a different world, though, because IR reflectance and color don’t correspond well to visible-light reflectance and color. My black T-shirt, the one one with the mock MPAA rating on it reading “XYZZY – WARNING: FULL FRONTAL NERDITY – Tech-Challenged Persons Strongly Cautioned”, appeared pale green. A bystander commented “That’s how you tell the real Goths from the fake Goths.” I of course rounded in him in mock indigation, because what self-respecting geek would want to fake being a Goth?
Then we turned the camera on my wife Cathy, who was elegantly turned out in a black cami tank top, a black blazer, and a titillating amount of visible skin. The tank-top looked dark in the image, but the blazer was a shade of white a few degrees blue-shifted from her skin tone, and seemed to glow as though by specular reflection or emission rather than diffuse reflection.
“Hmm. I wonder why my jacket looks like that?” asked she.
I saw my moment. “Because,” I intoned, “you are a hot chick.”