Grey cards for film Photography and digital Photography

Started Mar 13, 2013 | Questions thread
The Sage Knows
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You mean Exposure vs Neutral Reference Cards
In reply to Albert Drybrae, Mar 19, 2013

In the old film days an 18% grey card is a darker grey than the grey cards used for digital photography. Can anyone explain this?

Al

What you are referring to are the newer white balance or neutral reference cards used for digital photography. Companies like XRITE, WhiBal, and others make them so that you can perform a manual white balance in camera or include them in a sample shot so that you can have a calibrated neutral tone with which to use an eyedropper in Photoshop, Lightroom, etc to make an accurate white balance adjustment. DO NOT USE THESE FOR EXPOSURE SETTING.

The 18% gray cards you referred to were (and still can be) used for exposure setting. They are not as good for white balance setting for three reasons:

1. Because they were never meant to be perfectly neutral at all visible wavelengths My old Kodak cards from 10 years ago were ever so slightly greenish. The reverse 90% side wasn't a real accurate white either. The new Kodak cards a much more neutral gray. You can still get them from B&H.

2. The darker gray results in an image that is more prone to color noise making it harder to find a typical grouping of pixels with which to work with when using an eyedropper to set the WB in post. You can get significantly different wb results just by clicking around the same gray patch.

3. More digital data is stored in lighter tones than darker tones. So with more data, there is more flexibility to shift RGB numbers around and achieve a good white balance. This is explained in detail on Whibal's site:

http://www.mtdhelp.com/kb/whibal/is-the-whibal-the-same-as-an-18-gray-card

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Robert

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