[argyllcms] FWA compensation.

  • From: Roger Breton <graxx@xxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 10 Mar 2008 21:03:07 -0400

Compare the spectra with and without the UV-cut filter mounted on the
instrument : the two superimposed spectra tell the story?

To apply your heuristic, I suppose you need two datasets with spectral data,
one measured with the UV-cut filter and one without.

My only interrogation, Graeme, is do you end up calculating some kind of
global correction or do you apply it 'selectively' according to the hue
angle or chroma?

I was working with a new press profile today and with a measured white of b*
= -4.65, there is no hesitation that this paper exhibits moderate
fluorescence. When viewed under a 300 to 365nm fluorescent UV "light", this
paper glows.

I toyed with the idea of changing the Media White Point in the resultant
press profile, for something less bluish like b* = -2.00, but I'm not sure
this is enough. 

I use two proofing papers, one by GMG, containing no OB, and one by Kodak,
containing a moderate level of OB, with a b* = -3.5.

I always believe the theory of Martin Open about matching the level of OB in
the press paper to the level of OB on proofing paper, but I can tell you,
for having experimented with this, that it does not work. It works better
for some images than proofing to the GMG media but it's not the panacea.

I find myself with a dilemma: a) I re-measured the press targets (ECI02r)
with a UV-cut filter and see what kind of results I get on both proofing
media I use, or b) edit profiles using some ICC profile editor.

I have this because, either way, it's a fudge. Unfortunately, in the
presence of OB, colorimetry cannot help me.

> The technical way to confirm this is to compare the white
> spectrum with and without UV. Some instruments allow this,
> such as the Spectrolino and XRite DTP70 (where you can put
> the filter on and off), and the i1iSis can take
> readings with and without UV illumination.

Roger Breton 

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