Re: Colorimetric Accuracy in the Field
Re: Colorimetric Accuracy in the Field
- Subject: Re: Colorimetric Accuracy in the Field
- From: Graeme Gill <email@hidden>
- Date: Fri, 07 Jun 2013 09:53:44 +1000
Henry Davis wrote:
> Nobody is saying that the illuminant isn't a hugely important factor.
The main reason that the illuminant is a factor is that many/most cameras
aren't colorimetric. By that I mean that their spectral sensitivities
don't match a human observer. If they did, and their (light level)
linearity was known, then (by definition) they'd be a high spatial
resolution colorimeter.
The practical situation is analogous to the one with cheap display
colorimeters: They can be very accurate with a correction matrix if the
spectral nature of the samples they are reading is known. With a display
device that has colors that are (largely) a liner combination of the three
primary spectra, a matrix does nicely. For a camera, it can't be that
easy, because real world object colors are composed of many metamers,
and the spectrum hitting the camera sensor is that times the illuminant
spectrum. So a "calibration" matrix can fudge it for a range of expected
object spectra x expected illuminant, but ultimately it's going to work
the best over the widest range of conditions if the camera spectral
sensitivity is closer to a human observer.
It would be interesting to know which current cameras best fulfil this ideal :-)
Such a camera would capture "what you see" with much less need for manual post
capture tweaking.
Graeme Gill.
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