Odd question: Exposure and White Balance

So, this seems like a weird question, but does exposure affect White Balance?

For example, I picked up a Lastolite EzyBalance card...do I need to set my exposure BEFORE taking the WB reference shot off of it? Or does it not matter?

Thanks!

Are you talking about using the card to set a custom WB in-camera?

Yes...should have been more clear.

Well, it does appear to matter that you must exposure the WB target accurately. I checked my camera manuals and they all say either under- or over-exposure may affect the accuracy of the white balance.

Here's what my 1D Mark III manual says, for example: "Shoot the white object so that a standard (gray) exposure is obtained. If it is underexposed or overexposed, a correct white balance may not be obtained."

So in other words you want set an exposure so that the histogram of your WB reference shot is to the right of the center but not to the right edge (no clipping).

If you choose the WB eyedropper in LR, it's more accurate on white then on dark gray.
If you first WB, then adjust exposure, you might get a hue shift, depending on the DNG profile you use: http://dcptool.sourcef​orge.net/Hue%20Twists.​html

Apart from that: AFAIK, It doesn't matter. You can WB on a white (not blown!) or a dark gray piece of paper. And that is regardless of the actual 'brightness' of the paper

No matter what the manual says, I usually expose a gray / white paper "well" (middle gray or about a stop above), and use that for CWB. Never had problems. Then again, I usually re-do it in the Raw converter...

PixelMagic wrote in post #12410186
Well, it does appear to matter that you must exposure the WB target accurately. I checked my camera manuals and they all say either under- or over-exposure may affect the accuracy of the white balance.

Here's what my 1D Mark III manual says, for example: "Shoot the white object so that a standard (gray) exposure is obtained. If it is underexposed or overexposed, a correct white balance may not be obtained."

I think that is Canon covering their collective butt lest somebody over or under expose to the point of clipping. As René says, a card exposed ETTR without clipping should have the advantage of more photo data and less noise.

All true...the same advice regarding correct exposure in in my ColorChecker Passport manual. I'm thinking along the lines of blowing the red channel through overexposure, for example, could fool the camera into calculating an incorrect WB.

I agree that its more accurate the way Rene describes.

René Damkot wrote in post #12410244
If you choose the WB eyedropper in LR, it's more accurate on white then on dark gray.
If you first WB, then adjust exposure, you might get a hue shift, depending on the DNG profile you use: http://dcptool.sourcef​orge.net/Hue%20Twists.​html

Apart from that: AFAIK, It doesn't matter. You can WB on a white (not blown!) or a dark gray piece of paper. And that is regardless of the actual 'brightness' of the paper

No matter what the manual says, I usually expose a gray / white paper "well" (middle gray or about a stop above), and use that for CWB. Never had problems. Then again, I usually re-do it in the Raw converter...

tzalman wrote in post #12410286
I think that is Canon covering their collective butt lest somebody over or under expose to the point of clipping. As René says, a card exposed ETTR without clipping should have the advantage of more photo data and less noise.

I've always wondered whether when making a CWB the camera uses RAW data - which would seem to be indicated by the fact that you can photograph the target card with any WB set, or whether it uses rendered (jpg) data - which would seem to be indicated by the instruction that you can use any Picture Style except B/W. If it uses the RAW data, the chances of a blown red channel are reduced but you could blow the green alone.

Thanks, folks!

tzalman wrote in post #12410439
I've always wondered whether when making a CWB the camera uses RAW data - which would seem to be indicated by the fact that you can photograph the target card with any WB set, or whether it uses rendered (jpg) data - which would seem to be indicated by the instruction that you can use any Picture Style except B/W. If it uses the RAW data, the chances of a blown red channel are reduced but you could blow the green alone.

Hmm, interesting question -- I guess it would either use the jpeg rendering of the target or else calculate as it is interpreting and rendering the jpeg, either way I guess would work but I don't have a clue as to how it actually works!