[argyllcms] Re: Use of DTP-22 digital swatchbook with Argyll CMS

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 05 Feb 2007 11:33:17 +1100

Mario Becroft (mailing list) wrote:
it look white--either that or my DTP-22 is reading wrong. But I tried
reading some other paper with it, and while most of the papers I tried
seemed to have a similar cyan bias according to the DTP-22, there were
several which were exactly white--so I guess the papers really do vary
and you just can't see it.

Sounds suspiciously like FWA (Fluorescent Whitener Additive) effects. You
can get any sort of blue/non-blue shift depending on how the viewing
conditions compare to the lamp in the instrument (which is usually
incandescent 'A' spectrum) and the level of FWA in the paper, and
also depending on the differences between source and destination.

If you have a tool for plotting the spectrum, it's quite obvious when
there's FWA in the paper - measure white, and it will have a peak
at the blue end from the fluorescent emission, and a steep slope into the
UV where the absorption is. A paper with no FWA will have no peak, and only
a mild decline at the UV end.

Many typical viewing conditions are UV poor compared to an incandescent
lamp (i.e.., typical fluorescent lamps have phosphor that absorbs UV, a lot
of light fittings are covered by normal glass or UV stabilized plastic,
which absorbs UV), while other situations (such as sunlight unfiltered by
glass, or a true D50 spectrum) are rich in UV compared to an incandescent lamp.
Some of the so called "D50" viewing booth tubes have a special UV emitting
phosphor to emulate unfiltered sunlight (i.e.. GTI), while others viewing
booth lights emit almost none. FWA plays havoc with visual matching as a result.

Graeme Gill.

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