Re: Light indicator band issues.
Re: Light indicator band issues.
- Subject: Re: Light indicator band issues.
- From: Graeme Gill <email@hidden>
- Date: Tue, 19 Nov 2013 08:49:26 +1100
Mark Stegman wrote:
> You are teasing us. Please elaborate. I had the same 'ambitions' as Axel but only
> mirrored his disappointment.
Hi,
sorry, this is the most basic of basic color science. Tri-stimulus
matching depends on metamarism. Two colors are assumed to match if the
spectrum reaching our eyes triggers the same response in our retina.
Our eye's spectral response is modelled by the standard observer matching
curves. A painted surface will reflect a spectrum that is the product
of the illuminant spectrum and the reflectance spectrum of the paint.
So the two paint colors on the test strip will only perfectly match
if the illuminant spectrum times the paint spectrum returns a metameric
pair - two spectra that trigger the same response in our retina.
None of the test patches seemed to specify what spectrum they
are expected to match under. A color temperature certainly
isn't a spectrum. Now it's possible the test patches were
setup to match under "typical" viewing booth illuminant,
but who knows, they aren't saying what that is.
There is also a limitation imposed by what ink formulations
are available/practical. Even if it was intended to match exactly
under your particular lamp, it may be too technically difficult
to formulate an ink pair that will do so perfectly.
> What exactly is 'sufficient' to achieve a match with a metameric pair?
The usual - 1 delta E !
[In practice there is a whole family of illuminant spectra that
will give a metameric match. The interesting question is how
similar that family is to standard D50 viewing illuminants! ]
> If these things are so inadequate why does UGRA/FOGRA/GATF market them?
I'm sure they have a purpose, but they are being rather
sloppy in the specifications, and misleading in when they
can be expected to "work".
Graeme Gill.
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