[argyllcms] Re: FWA compensation.

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 10 Mar 2008 23:20:53 +1100

Amin Gharehchaie wrote:

I bought a package of permajet sample papers and there I tried a paper that permajet says does not have any Optical Brighteners, but Argyll tell me that the FWA content = 0.637455

Argyll uses a heuristic to estimate the FWA content. Without measuring
with and without UV illumination, it's not possible to make a definitive
conclusion about FWA content. The spectral shape of the paper
you are using has a rather "rounded" spectrum into the blue, and
the heuristic doesn't do a very good job of estimating the
presence of FWA, since it is expecting white paper, with a
more straight line characteristic. You really need to examine the spectrum
of the paper to make a judgement about whether FWA compensation is
going to be appropriate of not. This is pretty easy to spot
visually, but paper with odd spectral characteristics (tint) will fool
the algorithm used.

From what I can understand is that the optical brighteners are actually in
the ink and not the paper, and Gretag checks only against the paper but Argyll checks against paper and ink.
Is this a correct assumtion?

No. Nothing in Argyll will help you if you have ink that fluoresces. You
need a quite different instrument and software to deal with such a situation.

Graeme Gill.

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