Re: was: Brightener in Epson Premium Glossy
Re: was: Brightener in Epson Premium Glossy
- Subject: Re: was: Brightener in Epson Premium Glossy
- From: Graeme Gill <email@hidden>
- Date: Tue, 01 Oct 2002 12:08:33 +1000
Adriano Von Markendorf wrote:
>
Very intersting subject. I hear somany times the same argument.
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I wondering if this kind of problem could be cause problems reading pure
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yellows patches, I mean, the resulting profile come with somany cyan and/or
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magenta - more noticiable in 100Y using semmigloss media (some uv, about 4)
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and Guardian inks -
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A very funny thing is, I get practically the same problem using Colorblind 4
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and ProfileMaker 4, I haven't tested with PO 4.
In my experience, the issue of getting non-pure yellows when trying to
emulate a larger gamut with a smaller gamut device, is all about the
type of gamut mapping/clipping being used. Profiling packages that
use a simple geometric approach (mapping out of gamut colors towards
a central point for instance) often have this problem. Profiling
packages that map out of gamut colors towards the closest in-gamut
colors tend to have purer yellows.
>
Could be better use a non-UV reader with a diferrent light source like
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spectrocam? they claim to get better espectral response (lees uv reading and
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a little more wavelenght range) from your xenon light.
A lot of instruments use an incandescent light source similar in spectrum
to the standard "A" source. It is generally assumed that in Graphic Arts
that standard viewing conditions will be a daylight spectrum of D50 or
D65 color temperature. Many practical viewing conditions are actually
fluorescent simulators of D50 or D65, which in fact have a similar
white point but rather different spectrum.
The claim of an instrument like the spectrocam, is that their
xenon light source is more like the real viewing condition of D65.
If in fact you have a viewing booth with real D65 spectrum (I don't
know how this would be done economically, and it's hard to know when
real daylight is exactly at 6500K), then, yes, this should
help enormously in accounting for fluorescent whitener effects.
The problem is that most of the D65 viewing booths out there
aren't a real D65 spectrum, and could have quite a different
balance between their UV and non-UV illumination levels,
leading to a mismatch between the xenon instrument,
and the viewing booth.
I've looked at the spectrum of a couple of fluorescent D50
viewing booths with tubes from different manufacturers, and while
the visible spectrum and white points were very similar, they had
quite noticeably different emissions in the UV wavelengths. Paper
with large amounts of fluorescent whitener in them, could therefore
be expected to look somewhat different in the two booths.
>
I saw in the list comments about this capacity of abstract the uv component
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from PM4.
It's not really clear exactly what PM4 does. I got the impression that
it was some sort of "rule of thumb" compensation for fluorescent whitener,
but it's hard to tell if that is all it is, or whether it is something
more sophisticated.
Graeme Gill.
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