[argyllcms] Re: Argyll CMS as a spectroradiometer
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 21 Oct 2010 17:21:11 +1100
Jeremy Pronk wrote:
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.151.6187
A problem with this paper is that they claim to have solved the
problem of a change in scene illumination. I can't see how they
have done that, since it's inherent in tri-stimulus colorimetry,
when the camera does not meet the Luther condition. The only
way of solving this is to spectrally characterize the cameras
sensors, and this is very hard to do without using a monochrometer
based measurement technique, and they don't refer to any of the
more difficult techniques for avoiding that.
If they are merely referring to the fact that by default an instrument
will read D50 based XYZ values from a reflective target, then this
is easily tackled by measuring the spectral reflectance, the scene
illuminance spectrum, and combining them to compute the XYZ
values for the scene illumination (Argyll will do this if you
supply a spectral input chart reference for instance.)
For their technique to work for different scene illuminants, they
would have to use the scene illuminant as the backlight for their
test target, and re-characterize each camera for that illuminant,
which is exactly the same situation as that for a reflective target.
Graeme Gill.
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