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Do I have to have the gray card on a specific angle while taking a photo for custom white balance calibration? Or it is irrelevant?

I am guessing that the gray card plane should be perpendicular (90 degrees angle) on the shooting axis but I am not sure

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1 Answer 1

up vote 16 down vote accepted

Ideally, you're shooting in an environment with controlled lighting (a single light source, or several tuned to same color temperature), your subject and black or white surfaces only. In this case, the angle does not matter - just take care that its exposure falls somewhere in the middle in your test shot (so you're not accidentally clipping a channel).

In the wild, the angle becomes significant, as it determines where the card gets its light from. E.g. same card held in same place tilted towards sun, towards blue sky or towards green grass will give three different white balances. So in such case, you should hold it roughly in the same place and on the same plane as the most important surface you need to have neutral colors - e.g. middle of face in a portrait.

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I have worked on a couple lit sets where we would shoot the card facing the lens and one facing the lights. it helped in the processing and with an effect known as metamerism –  underarock Dec 4 '12 at 17:06
    
@underarock this sounds interesting, I'd be happy if you could explain it further in an answer to my follow-up question –  Imre Dec 4 '12 at 18:28
    
Excellent answer, thank you! –  Andrei Rinea Dec 4 '12 at 19:20
    
the color of a surface will change under variations in lighting, (color of light, angle of light). facing the card at the light give the full reflected surface facing the light, facing the lens gives you what middle grey would look like perfectly perpendicular with the lens. Try facing one at the sun and one at the lens if you are outside –  underarock Dec 28 '12 at 16:58

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