Re: Creating a SWOP proof with an Epson
Re: Creating a SWOP proof with an Epson
- Subject: Re: Creating a SWOP proof with an Epson
- From: Terry Wyse <email@hidden>
- Date: Sun, 16 Jul 2006 09:59:00 -0400
I've never quite understood the logic or argument of using a UV-cut
spectro for linearization. I'll include an example at the end of this
post of what I've heard the logic is about and why I think it's
flawed. But I digress...
Dave, as far as you not being able to use your non-filtered Eye-One
as ColorBurst "requires" a UV-cut spectro, the problem is worse than
that. If I'm not mistaken, I believe ColorBurst uses by default a UV-
cut X-Rite Pulse spectro for all their canned linearizations. So even
if you had a UV-cut Eye-One, your linearization would not match
theirs due to the differences in instrumentation. The differences
between instruments is not trivial in my experience. If I had a
working Eye-One here I'd be willing to test this but I don't at the
moment.
As to the non-filtered vs. UV-cut theory for linearization....
From what I understand, it has mostly to do with measuring the the
yellow ramp on a paper with a significant amount of optical
brighteners. Let's see if I can explain it adequately...
Let's say you have a media that measures L* 97 a* 0 b* -5 with an un-
filtered spectro. We'll focus on the b* value as that's what's
relevant here. When you're measuring the yellow ramp, at 0% you'll
get the full b* -5. As soon as you start adding yellow ink, which has
a +b* value, you'll get to a point where the spectro will measure a
"neutral" value and essentially see the yellow ink as gray. Example:
0% = L97 a0 b-5
1% = L96 a0 b-3
2% = L95 a0 b0 <-----
3% = L94 a0 b+2
4% = L93 a0 b+4
...and so on
You can see, in my bogus example, that at 2% the yellow ink has
effectively neutralized the optical brighteners in the paper causing
it to appear "colorless" or neutral. The argument goes that this will
fool the linearization application and foul up the linearization. In
ColorBurst's case, since they use chroma for linearization, this sort
of makes sense.
The argument goes that since a UV-cut spectro would filter out or
cancel the effects of optical brighteners, you'd be starting at a
near-zero b* value for paper white and any amount of yellow ink would
result in a +b* value.
But that's only if you calculate your linearization based on absolute
values.
If you take your measurements but then "zero" out on the media (add
+3 L* and +5 b*), giving you relative instead of absolute values, it
works just fine....
0% = L100 a0 b0
1% = L99 a0 b+2
2% = L98 a0 b+5 <-----
3% = L97 a0 b+7
4% = L96 a0 b+9
So, unless I'm missing something, using relative readings to
calculate chroma (or whatever) would work just fine regardless of
spectro filtration. This would even make the linearization process
relatively immune to the differences in instrumentation. At least in
my observations, various spectros will differ by quite a lot in their
absolute measurements but they are pretty darn close when compared
"relative" to each other. This is also why that, even if you have two
spectros that measure quite differently, if the same spectros are
used to create both the source and destination, the results will look
very similar. But try mixing/matching spectros for source/destination
and you've got a recipe for distaster.
Some might argue that this method cancels out the effects of the
paper itself, rendering the paper as "zero" (L100 a/b0), but in my
opinion (and it's only an opinion) this would be the proper way to
LINEARIZE anyway. In all my years in prepress <slash> printing,
linearization/calibration is ALWAYS done relative to the substrate.
If it was film, you zeroed out on the clear base before measuring dot
%, if it's a plate the background metal is zeroed, on a press you
first zero out your paper. In fact, this is even fundamental to the
new "G7" methodology of press calibration; the press's tone curve
(NPDC) is calculated RELATIVE to the substrate.
My last argument "against" UV-cut spectros is based on visual
comparisons of proofs. In every case I've observed, it certainly
appears to me that the non-filtered spectro ALWAYS produced the
superior visual match as compared to taking the same measurements
with UV-cut filtration. For this reason, I've pretty much settled on
non-filtered measurements when going for critical color proofing
applications.
Regards,
Terry Wyse
On Jul 15, 2006, at 11:49 PM, Dave Tuemmler wrote:
We have the lite version of ColorBurst that came with our 4800
Pro. The software requires a spectro with a UV to linearize. We
have an Eye One but not the UV version & I'm not eager to spend
$1500 for another i1. I'm assuming re-linearization would be a
benefit. I guess the question is how much do you think it will
matter. I'm also thinking of upgrading to the full version so we
can load custom profiles.
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