White balance and Gray cards

Was just thinking about white balance and gray cards. I was wondering if it matters if your white balance is off when you take a gray card reading to get a proper exposure? Does color temp. affect a gray card reading?

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Permalink Reply by Philip Gann on March 11, 2011 at 2:42am

Just trying to get my head around the question to make sure I understand it correctly but this is what I do when using a Grey Card to set White Balance. First I set the camera to Auto WB so that it can automatically determine the nearest WB setting. I then look at what that WB number is and set the camera to that WB. Now this works well if the light is not going to change during the shoot such as an indoor lightting setup.

If however I am going to be in a situation where the light will be changing I take a shot of the Grey Card in Auto WB and then use that shot during post processing as the guide to the correct WB for the subsequent shots however I do not automatically apply this to everything without making a judgement decision whether I like the actual resulting WB or not. Some images just look better slightly warm or cool and a neutral WB can destroy the mood.

As I always shoot in RAW mode making the correction in post processing is fairly straight forward providing your monitor is colour corrected first.

Now the bit of the question that has me confused is relating to proper exposure. WB and Colour Temp don't effect exposure as far as under or over exposure of the image only the colour bias of the image.

This is how I approach the use of Grey Cards and I'm sure there will be plenty of other methods used.

Regards, Philip

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Permalink Reply by T. Williams Photography on March 11, 2011 at 3:58am

"Now the bit of the question that has me confused is relating to proper exposure. WB and Colour Temp don't effect exposure as far as under or over exposure of the image only the colour bias of the image."

This is what i was wondering about, wasn't sure that if my wb was off if that would affect the exposure reading I got from the gray card.

Thanks for the reply and clearing that up for me.

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Permalink Reply by CameraClicker on March 11, 2011 at 2:55am

The question that comes back is are you shooting raw or JPEG?

If you are shooting raw, set white balance to auto and you can change it to whatever value you wish later. Shoot the gray card as a reference for processing later.

If you are shooting JPEG, take the opportunity to set custom white balance with the gray card.

It does not affect the exposure but conversion to JPEG throws out so much information that if the white balance is set incorrectly you may not be able to recover it.