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Today's Topics:
1. Presses and G7 (Brian Lawler)
2. G7 press calibration, best press conditions or average?
(Paul Foerts)
3. About "average" press condition and calibration (Roger Breton)
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Message: 1
Date: Sat, 1 Nov 2008 12:47:17 -0700
From: Brian Lawler <email@hidden>
Subject: Presses and G7
To: email@hidden
Message-ID: <email@hidden>
Content-Type: text/plain; charset=WINDOWS-1252; format=flowed;
delsp=yes
Greetings,
A printing press is, as Rick McCleary said, a complex process
involving a machine, a person (or several), and a whole system of
process controls.
Nothing stands alone in the process, and nothing can be isolated from
the other parts, as that breaks the chain of complex events that is
printing.
G7 can be one of those process steps, and if used correctly, can
reduce the variability of production that is experienced by most
printers.
Another equally important factor, one that is seldom mentioned, is the
quality and consistency of ink.
If inks are purchased and used without testing for color consistency
and acceptability, then the G7 gray balance will break, and the
process will go out of control.
Many of the best printers hold their ink suppliers accountable for the
color and the make-up of ink. When the acceptability standard is
reached, then the press can run within the tolerances under which G7
balance was achieved.
Many printers also have ink manufacture and quality measurement in-
house, ensuring that they have constant control over that variable.
One could argue that paper, blankets, packing and other parts of the
process are equally important, and they are. It is important to
evaluate as a series of interlocking steps, each of which must be
monitored with care and caution.
The best printers are those whose process is meticulously monitored
and adjusted for consistent quality every step of the way.
Best wishes,
Brian P. Lawler
------------------------------
Message: 2
Date: Sat, 01 Nov 2008 23:01:24 +0100
From: Paul Foerts <email@hidden>
Subject: G7 press calibration, best press conditions or average?
To: <email@hidden>
Message-ID: <C5329044.4F99%email@hidden>
Content-Type: text/plain; charset="ISO-8859-1"
On Fri, 31 Oct 2008 16:09:31 -0500 Steve Miller <email@hidden>
wrote:
Paul,
A conventional offset printing press cannot be "calibrated".
Presses are
"adjusted" by press operators.
I used the words "press calibration" because that's what most
people I've
talked to call it. It's easier than saying "Using the G7
methodology to aim
at an ISO standard printing condition".
There's a trending software available and is described as follows...
"A product that is designed to help printers save money in the
pressroom by
helping: Reduce the cost of calibrating a press to an ISO12647
based print
specification."
Then it goes on to say...
"What does it do?
Calibrate Press Gamut to ISO12647
Assist press operators in calibrating their press to ISO12647 based
print
specifications. (FOGRA/GRACoL/SWOP)"
Then there's IDEALink Curve software that's described as the
following...
"IDEALink Curve is your link to simple G7 implementation. Easily
calibrate and verify all your systems without the tedium and
uncertainty of
manual curve drawing."
Yes this is what marketing does with existing technology...
If the technology isn't sexy enough, put some voodoo over it and it
will
sell like "new" cakes!
G7 implementation = nothing else than "using the G7 methodology to
aim at an
ISO standard printing condition"
G7 methodology = TV (tone value) adjustment using c-t-p curves
(simplified
basic definition).
Nothing gets "calibrated". If others like to call adjustment or
setting
"calibration", well, so be it. I suppose they'll agree to call all
operators
"calibrators" too. :-))
Paul
------------------------------
Message: 3
Date: Sun, 02 Nov 2008 09:29:10 -0500
From: Roger Breton <email@hidden>
Subject: About "average" press condition and calibration
To: 'Mike Strickler' <email@hidden>,
email@hidden
Message-ID: <000d01c93cf7$5f2775a0$1d7660e0$@ca>
Content-Type: text/plain; charset=us-ascii
This is another ongoing argument in the trade.
For my part, I favor starting with new blankets, new, fresh fountain
solution, fresh everything. Squeeze needs to be re-adjusted between
the form
rollers and every simple adjustments checked. I know some tradesman
advocate
calibrating in an "average" condition but that, to me is not the
true spirit
of calibration which is, as was repeated many times on this List by
many
contributors, the idea of putting the device in a *known* condition.
As Mike
said, when the ***it hits the fan, it's always possible to fall back
on some
known state and ask the question, what is it that changed?
Otherwise, it's
not possible to know what changed. Because there are no documented
reference
point.
The one problem I keep seeing on presses of all kind is the lack of
controls
on the all too critical ink/water balance, as part of press
calibration.
There exists some ink film thickness gauge that can be used, when
the press
is stopped, to sample the ink film on the oscillator. But that's
hardly
"online". The problem is that every press operator will set the
dampener
system according to their judgement and experience (and taste too).
Most
operators I know will take the time to walk up to the units and
observe the
plates in rotation, as the press runs, and if they see a satiny
look, when
looking at the press from an oblique angle, they'll know they don't
have too
much water on the blanket. Some will go as far as making the press
scum and
then raise the water back up until it does not scum anymore. That's
another
trick. But that's hardly scientific. And to think that newer presses
now
have these auto plate loading system, that completely hide the
plates as the
press runs, some other heuristics has to be found, obviously. I
don't know
how these pressmen do but this ink/water balance issue, when
everything else
is in control, can easily derail any characterization or calibration
efforts. Let's not forget that some paper absorb more than others
and need
more water than others. The trend with precipitated calcium carbonate
coating being used more and more in manufacturing to cut costs down is
another nice wrench thrown into the mix. I wish there was some way
of truly
monitoring the ink film characteristics as the press is running.
Gosh --
even ink suppliers are dumbfound by this issue : no one has the
definitive
answer. And say that wew presses keep coming out with the same
illogical
ink/water designs, it's like no one is learning? Hello? We have PDF,
ICC
profiles, Device Link Profiles, GMG RIPs, the G7 method, the iSis,
wide
gamut LED monitors but we're still in the stone age of controlling
something
as basic as ink/water balance?
I think I'll have that second cup of coffee now...
Roger
If the press is in its best condition with new blankets you have a
reference baseline to return to when things go awry. You can't say
the same of "average" condition.
Mike Strickler
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