White Balance Misconception


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Jun 18, 2005
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#1
Using a white card to manually adjust white balance, it is possible to achieve a picture without colour casts. But I've heard people saying that white remains white in whichever colour temperatures/lighting. Is it truely so? I've been thinking about it and realized that a white card placed under red light would be red. So the white does not remain white?
 

Hobbes234

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#2
megascriler said:
Using a white card to manually adjust white balance, it is possible to achieve a picture without colour casts. But I've heard people saying that white remains white in whichever colour temperatures/lighting. Is it truely so? I've been thinking about it and realized that a white card placed under red light would be red. So the white does not remain white?

White is made up of the 3 primary colours, red blue green. (equal amts)
as long as there is a reasonable amount of red, reasonable amt of green and reasonable amt of green. our eyes tell us that it is white (even though they are not the same).

The camera is able to pick up the slight differences hence we have to tell the camera that the "colour" object that we are seeing is white. (camera automatically compensates the difference between the red, blue and green) so that white remains white.

our eyes are Not able to detect slight differences unless we put them next to another sample we will not be able to tell the difference.

As to your question about the red light, there is no other colours except red so the card will not be white.
 

VR2

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#4
hwchoy said:
isn't WB calibration done with an 18% grey card?
i tot dis is for correct exposure of bright and dark places..
 

jbma

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#6
I don't think there is a misconception here but just a misunderstanding.
 

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#7
Has anybody actually cheated the camera?
telling the camera that blue is white, yellow is white, red is white, etc.
The effects are actualy similiar to adding a blue or yellow or red filter?
I tried once to cheat the camera light blue is white,
and while shooting an ang moh's kid, the skin tone appears to be very nice...
 

ExplorerZ

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#8
scaredcloud said:
Has anybody actually cheated the camera?
telling the camera that blue is white, yellow is white, red is white, etc.
The effects are actualy similiar to adding a blue or yellow or red filter?
I tried once to cheat the camera light blue is white,
and while shooting an ang moh's kid, the skin tone appears to be very nice...
im pretty sure that everyone that does IR photography cheated their camera :bsmilie:
 

alexj

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#11
The idea of WB on grey or white card is similar. If you use an 18% grey, you know its accurate cos you paid a fair bit of $, so it better be neutral (unless you mistreat it). For white, there are 2 things:
1. Are you sure your white is white? Your A4 paper might be carrying a slight warm or cool tone... but if you're in a rush, it's a quick fix. Generally it works okay unless you want dead accurate WB.
2. Are you sure your camera isn't overexposing the white? If your white paper is clipped off the histogram, you aren't going to get any colour.
 

#13
hwchoy said:
ok, specifically on canon DSLR, when you select an image for custom wb, it should be the image of a gray card yes?
it can be a white card...cos when you shoot an image, the auto exposure will still underexpose the shot to make the white a grey, unless you +1 or +2 stops...
 

Jun 18, 2005
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#14
But grey cards are better than white ones right? Since white does not remain white in drastic coloured lighting but grey does since it is neutral?

And thank you to everyone for answering my previous misunderstanding.
 

zeith

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#16
megascriler said:
Using a white card to manually adjust white balance, it is possible to achieve a picture without colour casts. But I've heard people saying that white remains white in whichever colour temperatures/lighting. Is it truely so? I've been thinking about it and realized that a white card placed under red light would be red. So the white does not remain white?

Interesting.. I wonder what will happen to the photo if we place a white card under red light and set custom white balance using that?
 

VR2

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#17
zeith said:
Interesting.. I wonder what will happen to the photo if we place a white card under red light and set custom white balance using that?
try out and let us know.. :p
 

catchlights

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#18
hwchoy said:
catchlights, is there a difference in doing custom WB (I am using 20D) using a 18% gray card or a white card?
It is easy to find a white object, a white paper or card to do a custom WB, and the cost is almost zero, however, a gray card will be better, since it calibrated to be neutral, but a gray card is costly, and not mean for casual shooters, so most camera manual do not stress on using a gray card for custom WB.

and alexj has given a detail explaination about using a white card.

Hope these help.
 

hwchoy

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#20
catchlights said:
It is easy to find a white object, a white paper or card to do a custom WB, and the cost is almost zero, however, a gray card will be better, since it calibrated to be neutral, but a gray card is costly, and not mean for casual shooters, so most camera manual do not stress on using a gray card for custom WB.

and alexj has given a detail explaination about using a white card.

Hope these help.
thanx I use a gray card normally but I had to use a laminted white card when customising WB for shooting through water!
 

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