Need help understanding white balance...


TPF Noob!
Jan 13, 2012
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Hey guys,

I was showing a co-worker the difference in an outdoor shot using a polarized filter vs not using a polarized filter (the difference was tremendous, btw).

His response was "can't I just do the same thing with adjusting white balance?"

My answer was "I don't think that's how white balance works", but it made me realize that I can't explain how white balance settings work, and how they differ from what a polarized filter does.

Can someone explain to me:
1- the basis of what white balance adjustments do?
2- how this differs from a polarized filter?

I would be indebted to you. And as Shrek said "someday, I will repay you... Unless I cannot find you or if I forget." I'd add to that that my ability to repay in terms of photography knowledge would be lacking as you all already have far more than I do. ;-)

Thank you very much!

Someone will come on with a techie explanation I am sure....

White balance adjusts color for the light conditions you are in.
Polarizing filters, depending on your angle from the path of the sun, manage reflections, haze, and blue up your skies.
There are a number of factors involved in acheiveing accurate color -- the color in your photo is the color of what you photographed.

One factor is the color of the light. Light color is variable. Artifical lights come in different colors and those are different than daylight. The color outdoors changes during the day. Sunlight is a different color than skylight -- skylight is blue compared to sunlight.

To achieve accurate color the software that we use to process our digital photos has to start by knowing what color the light was. Assume you have a grey card. The card itself is colorless. If you place the grey card in blue light (open shade for example) and take a photo of it, should it be blue or grey? The software in your camera has no clue that the card is in fact neutral and colorless. The only way your camera can successfully record the grey card as grey is if it knows in advance what color the light was. Setting a white balance is telling the camera software what color the light was.

White balance is a software process accomplished by adjusting the levels at which the red, green, and blue data from the sensor are mixed during conversion from RAW to JPG.

A polarizing filter allows light to pass through at a single orientation. Direct light is random, and thus is only slightly and evenly darkened by a polarizer. Reflected light acquires the orientation of the object it reflected off of (be it someone's face, the surface of a lake, a microscopic water droplet at 40,000ft, etc...), so by adjusting the orientation of the filter, you decide which direction of reflected light is allowed to pass through. Polarizers are color neutral (they try to be anyway, the good ones actually manage), they are a directional effect, not a chromatic one.
Tha camera does not see the way we see.

Each light source type has a different color temperature.

Our brains constantly make adjustments to our perception of color to account for the different light color temperatures.

Cameras can't do that on their own. We have to tell the camera what color temperture light source we are using. We do that by setting the White Balance, though white balance is mostly about the other colors.

That is why the white balance setting choices include Direct sunlight, incandescent, flourescent, flash, cloudy, shade, and others depending on the camera. A common issue with white balance occurs when a scene has more than one light source type. The camera can only completely correct for 1 color temperature at a time, othewise it can only partially correct for each different light source.
One way to address that issue is to gel one of the light source types so it is the same color temperature as the other light source, like gelling your flash unit to use in a room lit by overhead flourescent lights.
There is less and less incandescent lighting around, because a lot of it is being replaced by CFL (compact flourscent lighting).

The color temperature of sunlight changes somewhat through the day. Flouescent lighting comes in a fairly wide range of color temperatures. Some indoor lighting is mercury vapor or high pressure sodium lighting.

Understanding White Balance
Thank you everyone for your very helpful answers. I'll keep those in mind, do a bit more reading, and be able to talk with him more intelligently next time. :)


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