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In a comment to my answer on gray card angles, @underarock mentioned having used several gray card shots at different angles to cope better with metamerism.

This sounds intriguing, but I'm still not quite sure how that would work out in practice. Any hints?

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Metamerism is an effect that's usually (in photography) associated with viewing prints, especially ink jet prints. Dye based inks, and to a lesser extent pigment inks can appear to be color shifted depending on the type of light they are viewed under. This effect varies with the ink formulation. I know of no way to control or minimize this at the 'taking' end of the process.

What viewing the gray card in two different ways does do, however, is account for metamerism in the gray card by taking a measurement off of it when it's lit by the light illuminating the subject and then by the light that's hitting it from the point of view of the camera. Sometimes these are the same (in a studio for example) sometimes they are not.

In printing, one can compensate for metamerism by viewing a print under the light it's likely to be seen and correcting the colors accordingly. It's possible that photographing a gray card at different angles also gives a neutral-light and a neutral-dark that allows easier compensation.

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  • \$\begingroup\$ 'account for metamerism in the gray card' implies that the gray card should be printed with the same printer that will be used for the final prints. In other case, there will be a mismatch between color cast in the gray card and the final prints... am I wrong? \$\endgroup\$
    – Alberto
    Dec 10, 2012 at 12:28
  • \$\begingroup\$ Yes... Metamerism in the gray card only affects the way exposure and color balance is calculated in the camera or compensated for in your editing software. Metamerism in a print affects the color balance of the image when viewed as a print. \$\endgroup\$
    – BobT
    Dec 11, 2012 at 5:15
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Expanding upon BobT's answer:

Metamerism in the gray card is a non-issue with a high quality card. In fact, I'd argue that a gray card is not useful or acceptable if it's exhibiting metamerism. The basICColor Gray Card, for example, specifically addresses this, but it should be true of any gray card.

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