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Old Jan 17, 2004, 8:24 AM   #11
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White balance and exposure balance are not the same things.

You're comparing apples and oranges here.

A grey card is used for exposure determination....how dark or light the image will be based on the amount of light admitted to the camera's image sensor (film). Reflective meters are based on 18% grey. The "grey" refers to the tone, not the color. You could meter off a green card if it was a mid-tone. When speaking of tones, you must mentally desaturate the colors. Midtones are things like grass, medium blue skies, wet brown sand, etc. Concrete, white paint, snow are examples of lighter tones than 18%. Black, new blue jeans are good examples of darker tones.

White balance refers to the relative brightness based on the color temperature of the light source. Think back to film and consider what happens when you take a picture with outdoor film under flourescent lighting. Without filtration, you'll end up with a green cast. White balance in digital cameras does a similar thing, adjusting the relative brightness based on lighting conditions.

Both exposure and white balance can be corrected in post processing, but it makes more sense to me to be as close as possible to being correctly exposed before making any post processing adjustments in Photoshop. I shoot in RAW, so it essentially ignores any white balance settings that I place in the camera and I set the white balance in the RAW conversion process. I can also adjust the exposure at that point if I didn't get it right during set-up.


Brad, going back to your question. It will help provided you meter off it properly. The grey card must cover the entire metering range to be effective (i.e. spot metering or filling up the viewfinder for a matrix metering mode). Just having a grey card in the scene won't help at the time of exposure, but will give you a reference point during post processing time. (It would also give you a picture of a grey card in the middle of a basketball game :lol: )
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Old Jan 17, 2004, 8:34 AM   #12
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I remember reading somewhere that Caucasian skin is approximately 18% gray, but the card I have sure looks darker to my eye. Was the thing about skin wrong or is my perception off?

For white balance, I've found it a whole lot easier to keep a small card nearby with approximate temperatures written on it so I can quickly set the temperature on my camera. It's not always right on the mark, but it's close enough that little adjustment is required in Photoshop. And maybe the day will come when the settings will be committed to memory.
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Old Jan 17, 2004, 9:25 AM   #13
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Quote:
Originally Posted by bcoultry
For white balance, I've found it a whole lot easier to keep a small card nearby with approximate temperatures written on it so I can quickly set the temperature on my camera.
bcoultry the color temperature depends on the ligthsource illuminating the card... and not what's marked on the card!

ie the same card does not have the same reading under sunlight or tungsten lamps... in Kelvin for white balance.
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Old Jan 17, 2004, 9:33 AM   #14
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Quote:
Originally Posted by ohenry
White balance and exposure balance are not the same things.
agree
Quote:
Originally Posted by ohenry
You're comparing apples and oranges here.

A grey card is used for exposure determination....how dark or light the image will be based on the amount of light admitted to the camera's image sensor (film). Reflective meters are based on 18% grey. The "grey" refers to the tone, not the color.
The gray also referes to the color - the value of the reflected R, G, and B values are the same when "white" light hits it. Using a gray card for white balance should produce the same result as a white card because the camera will do its magic to adjust the color bias values so the result is R=G=B. Just what you want it to do and you really don't care if the camera thinks the light level is lower than it really is unless you are shooting in such low light it cannot do the white balance.

It is certianly true that you cannot simultaniously adjust the white balance and exposure with a gray card.
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Old Jan 17, 2004, 9:36 AM   #15
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Quote:
Originally Posted by bcoultry
I remember reading somewhere that Caucasian skin is approximately 18% gray, but the card I have sure looks darker to my eye. Was the thing about skin wrong or is my perception off?

The palm of a caucasian's hand is about a stop brighter than 18% gray card

Here's an interesting article on exposure:

http://daystarvisions.com/Docs/Tuts/Meter/pg2.html
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Old Jan 17, 2004, 10:32 AM   #16
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The article confirms the suspicion I've had about skin, a suspicion first arising from the knowledge that skin tones vary widely. I apparently correctly detected the difference between average skin tone and a gray card.

This also explains why, when I use a spot meter on a person's face, I often end up having to increase exposure compensation.

Thanks for the link.
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Old Jan 17, 2004, 4:56 PM   #17
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Bill, I guess since I don't mess with white balance in my computer I don't pay attention to adjusting it beyond AWB. I take care of that in post processing.

Barbara, anytime....those links always explain it better than I can! :lol:
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Old Jan 17, 2004, 5:22 PM   #18
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FYI

http://www.warmcards.com/digital_camera.html

:lol: :lol: :lol:
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Old Jan 17, 2004, 6:06 PM   #19
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Good information, NHL. But again, if we shoot in RAW mode, you can set your white balance to whatever you want and it doesn't matter -- or am I wrong here and white balance DOES affect the data written to RAW? From my understanding, the RAW file is unaffected by white balance settings.
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Old Jan 17, 2004, 6:26 PM   #20
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From my understanding, the RAW file is unaffected by white balance settings
That's been my impression also.
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