Can taking gray card shots at different angles help with metamerism?
Asked 12/4/2012
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I’ve seen a suggestion that photographing a gray card from several angles can help compensate for metamerism. How would that work in practice? Does changing the angle of the gray card improve color accuracy, or is metamerism mostly unrelated to capture-time gray card use?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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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.
Originally by user11772. Source · Licensed CC BY-SA 4.0
user11772
13y ago
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Not really. In photography, metamerism is usually a viewing/printing issue, especially with prints under different light sources, not something you normally fix by taking multiple gray-card shots at capture time.
What different gray-card angles can help with is not metamerism itself, but differences between:
- the light illuminating the subject, and
- the light reflecting toward the camera.
In some setups those are effectively the same; in others they may differ, so changing the card’s angle can change what light the camera “sees” from the card.
That said, a good gray card should be designed to avoid metameric behavior. If the card itself shows metamerism, it’s not a very reliable reference. With a high-quality gray card, metamerism of the card should be a non-issue.
So the practical takeaway is: multiple gray-card angles may help evaluate lighting/reflection geometry, but they are not a standard or meaningful solution to metamerism. For most capture work, one properly made gray card shot under the actual subject lighting is the right approach.
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