[argyllcms] Re: Argyll CMS as a spectroradiometer
- From: "Auke Nauta" <auke@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 21 Oct 2010 13:16:32 +0200
Dear Graeme,
I understand your point completely but I fail to see where are errors (if
any) in the cited pdf document.
(http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.151.6187)
They even show data with adjusted illuminant where the still get
acceptable results. Now having read it two times, I just don't see the
flaw(s)...
Do you have any clue?
Best regards,
Auke Nauta
Graeme Gill wrote:
> 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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