Quote Originally Posted by neuroanatomist


FWIW, the Canon manual suggests using a white card to set white balance. In reality, gray vs. white makes no real difference as long as they are spectrally neutral. The 18% gray card was primarily used for setting exposure, not white balance (because in the days of the gray card and manual exposure settings, white balance didn't exist - we bought color-balanced films for the conditions we'd be shooting in, with no way to change 'on the fly'). However, gray cards are spectrally neutral so they work well for setting a custom WB.
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The big difference with a white card is that it's easier to overexpose a white card than with a grey card. An overexposed &lt;neutral&gt; card will come up white "automatically" (all of the RGB values will be maxed out, and if R=G=B=max you have white).