Black and White

[Andy Finney <andy@xxxxxxxxxxxxxxxx>]

Josh wrote:

i have been photoing my girl in this particular
black out fit
and it always comes out white
have any of yall had this happen?


The colour of an object as we see it depends on what combination of 
red, green and blue it reflects when illuminated with white light.

If you extend that to infrared then different objects will reflect 
different amounts of infrared light and this may bear no relation to 
how they look in visible light. Just think of how a red object looks 
through a red filter compared to a blue one.

One very common thing in my experience is that man-made fibres 
reflect strongly in near infrared even if their visible colour is 
dark. What I don't know is whether this is related to the dye process 
or the fibre itself or one acting on the other.

A corollary of this (presumably) is that a man-made fibre will be 
cooler in sunlight than, say, wool of the same visible colour because 
it is reflecting the infrared portion of the light-energy falling on 
it. This is also why there is a danger of 'explosion' when you put a 
visibly opaque infrared filter over a flash gun. The visible light 
energy has to go somewhere.

OK: improvements on that explanation will be gratefully received but 
my guess Josh is simply that your gal's outfit is made of a man-made 
fabric or fibre-blend.

Cheers

Andy - Invisible Light
http://www.atsf.co.uk/ilight
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