What's going on with their hair?

February 1, 2009 11:29 AM

How does hair color appear on a night vision camera? Though I am embarrassed to admit that I watch Ghosthunters, I have noticed several times that the hair of the men who have brown hair on the regular camera appears to be a dark color on the night vision camera as well. But, the two female investigators named Kris, who appear to both be brunettes on the regular camera, look like they have blonde hair on the night vision camera. How can everyone be brown-haired on the regular camera, but some look blonde on the night vision camera?
posted by waywardgirl to grab bag (10 comments total)

Night vision cameras use infrared lights to illuminate the scene. This light cannot be seen by human eyes, but is easily detected by the CCD in the camera. In fact, digital cameras and camcorders include IR filters to reduce or eliminate this effect when shooting in normal light conditions. The night vision mode probably removes this filter.

So, this has to do with the surface reflectivity of the infrared light when it falls on these different surfaces. I would love to hear more about the science behind exactly what's happening at that surface.
posted by odinsdream at 11:50 AM on February 1

I guess my question is not so much about how nightvision works, but more about what is happening to their haircolors?

I don't understand what happens so that four people who have dark brown hair in natural light (Dave, Grant, Kris, and Kris) appear to be two blondes (Kris and Kris) and two brown-haired people (Dave and Grant) on the night vision camera.
posted by waywardgirl at 11:58 AM on February 1

My guess it that the female investigators dye their hair.
posted by horsemuth at 12:03 PM on February 1

We can't see the infra-red spectrum. To us, it all looks dark brown. However, maybe some brown hair is very (specular) reflective in the IR because of styling or products used, or because of the microstructure of the hair fibers. The IR camera packs the IR color spectrum as well as brightness all into just one visible (to us) color of varying brightness; some detail must be lost, or misrepresented.
posted by fatllama at 12:04 PM on February 1

Maybe it's hair-care products that are more reflective (or absorptive) of IR.
posted by zippy at 12:07 PM on February 1

Not an expert, but thought I'd throw in the theory that their hair care products may cause their hair to look different on camera.

Here's what I think WaywardGirl is talking about. A video of Dave & Kris under the Night Vision camera on Ghost Hunters. Notice that Dave's hair is dark, nearly black. Compare that to Kris' hair, which is very light, almost white on camera.

Looking at their profile pages on Sci-fi's site you'll see that Kris and Dave are not that dissimilar under natural light. Dave's hair is obviously darker, not nowhere the exaggerated amount seen in the night vision clip.

Here's a youtube clip of Dave, Steve, Kris, and Kris under blacklight.
posted by aristan at 12:19 PM on February 1

and by blacklight I mean Night Vision, d'oh.
posted by aristan at 12:20 PM on February 1

Apparently, as horsemuth alluded to, a lot of hair dye reflects IR. A lot of "active night vision" shines infrared, which we can't detect with our meat eyes, but which the camera can detect.
posted by porpoise at 1:44 PM on February 1

confirming with horsemuth - this happens to my girlfriends dyed hair on our IR security cameras as well. It does not with non-dyed hair.
posted by datacenter refugee at 4:34 PM on February 1

I would also guess that hair length is a factor - short hair all the hairs are pointing in different directions, thereby scattering the light more, and longer hair will have larger swathes of reflective highlights, making it look lighter.
posted by 5_13_23_42_69_666 at 7:19 PM on February 1