[argyllcms] Re: Using an i1 to measure FWA content?
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 10 Feb 2010 11:12:06 +1100
Gerhard Fuernkranz wrote:
For comparison, I'm wondering what's actually the situation with the
Color Munki? Isn't its light source UV-poor too? Is the SNR still large
enough at the very short wavelengths, so that the driver can still
safely divide the (offset-adjusted) raw readings obtained from samples
by the raw readings from the reference tile, w/o yielding "wild"
results? Or does the Munki simply not report this wavelength range at all?
The Munki is pretty hopeless below the peak of the LED, and the diffraction
grating seems particularly inefficient at short wavelengths too. The S/N
becomes even worse than the i1Pro with it's incandescent source at the very
shortest wavelengths, and the Munki extrapolates.
From a post to colorsync in Jan 2009:
> The ColorMunki wavelength range appears to be a bit more
> limited than the i1pro, with a reflective mode range of 430 - 730
> (the 380 - 420 readings being copies of the 430),
> and slightly better in emissive mode, 400-730 (380 & 390
> being copies of 400nm).
Btw, I rather don't think that the reflectance of the white reference
tile has actually a drop-off at about 400nm as suggested by the UV-cut
measurements, but I find it more likely that this apparent drop-off is
caused by the instrument (If manufacturer supplied reference numbers are
available for the white reference tile, then this could be easily verified).
For the i1pro the reference tile certainly rolls over at about 410nm. It's
reflectivity at long wavelengths is about 0.9, while it's about 0.7 at
380nm (according to the reference information). Presumably the spectrolino
is similar.
[This seems typical of many "white" materials. The only common thing I've
come across that doesn't do this is white polystyrene foam.]
Graeme Gill.
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