RE: G7 press calibration, best press conditions or average?
RE: G7 press calibration, best press conditions or average?
- Subject: RE: G7 press calibration, best press conditions or average?
- From: Roger Breton <email@hidden>
- Date: Mon, 03 Nov 2008 09:10:11 -0500
Mark,
Thank's for your two cents. You raised a number of interesting points.
> Let's start with calibration. I tell my students that the purpose of
> calibration is to get a device into a
> predictable and consistent state (which doesn't HAVE to be linear).
My thoughts exactly.
> This might be a digital printer,
> imagesetter, platesetter, monitor... This must take place BEFORE
> profiling: a process of capturing a
> description of the tone and colour characteristics of a device AT A
> SPECIFIC POINT IN TIME.
Interesting point. In the GMG RIP, it is key that calibration be done
*prior* to profiling. Otherwise, when re-calibrating every other week, let's
say, the profile would be rendered useless because it would no longer
describe the printer in a known, calibrated condition. Fantastic point! I
use GMG as an example but I'm sure everybody get the idea.
> The same applies to offset printing presses which are renown for their
> erratic behaviour over time. As
> others have pointed out there are many variables in this process and
> they have not traditionally been
> subjected to the same degree of quality control/scrutiny that occurs in
> other industries. Ink, paper,
> press and (unfortunately) press operator, not to mention temperature
> and humidity.
Yes, they have not. But I suspect they will as color management gradually
tightens its control on every variable involved in the process. But the
pressroom is a tough environment to change. It seems only when clients
complaint and threaten to take their business elsewhere that change can
finally be brought about.
> As a result variations in the printied product WILL occure even
> throughout a single run. Other
> factors such as age of the press and the quality of maintenance will
> aslo have an impact. It is
> unrealistic then to expect a single profile of the printing press to
> tell you much about what might come
> off the production line. When it comes to making a profile of a
> printing press the first question that
> should be asked is "What will the profile be used for?"
True. It's ludicrous to believe that one press profile will capture the
essence of the press behavior in its many moods and temper but that's what
we have to hold it against, nevertheless.
> Some of the practitioners in this field seem to think that the purpose
> of a press profile is to capture
> the press in an IDEAL state: when the press has just been serviced and
> all the variables are bolted
> down. But how REALISTIC is this profile? When you consider that (in an
> ideal world) this profile will be
> used by Graphic Designers (shock - horror!) as well as Prepress
> operators to predcit how their jobs are
> going to turn out there is a very real danger that they will be
> severely disappointed. Press profiles
> are not just for press operators. As Brian pointed out, the press is
> just one part of the production
> process.
That part of the process is not easy to deal with.
> This is the point of averaging profiles: to get a more 'realistic'
> picture of the capabilities of a press
> through the print run. An averaged profile will, by necessity, exhibit
> a colour space that
> is 'compromised' yet more readily achievable ON AVERAGE. This means
> that, when the designers and
> prepress use it to predict the result during soft and/or hard proofing
> they will see something that is
> achievable and realistic, not idealistic.
Right. The keyword here is realistic. But it has to be coupled with
customers's expectations. Some, as we know, are not realistic. Others demand
the utmost quality and are willing to pay for it. I think everything is
possible provided adequate resources are thrown at the problem in the form
of money and time. Heck! Look at what Bill Atkinson has done with its
Stones. We can debate all night long about the true quality of VanFu inks
but, in the end, I think Bill got away with some of the best quality one can
ever get from an offset sheetfed press. Never mind Hexachrome or stochastic,
just on the process control and repeatability of the whole system. As you
said, Mark, we're all looking for predictability. That's the holy grail of
this exercice.
> In other words, an accurate
> prediction of the end result. This, I
> thought, was the whole point of a colour management SYSTEM of which the
> press is one, not necessarily
> small, part.
Wow! I'm steeling the words off your mouth...
> You can even make an averaged profile across different printing presses
> to allow for the variation that
> might occur as a result of the demands of production schedules where
> the press targetted for the job
> is changed at the last minute.
For those who insist on making custom press profiles as opposed to using
ISO-type or CGATS-type synthetic datasets, such as GRACoL2006_X, I see the
need for better anylytical tools. It's one thing to aggregate a bunch of
measurement files, throw them in MeasureTool or PatchTool to average them,
but I see a missing link in the form of advanced statistical tools that
would allow analyzing a bunch of measurements files to extract meaningful
information about the underlying process. I have not see anyone doing this
in a commercial system, maybe that's too much to ask?
> Of course, if that press's
> characterisitics are significantly different the
> profile will be compromised again. It allows for more versatility in
> production management although the
> quality will be compromised. As long as it's within tolerance it's OK.
> Life is full of trade-offs. Especially on
> the production line.
Yes.
> This is the whole point of standards based printing. Instead of
> targtetting a particular printing press,
> you target a particular colour space: one that is achievable by the
> large majority of printing presses.
I'm with you 100%.
> This is, I would think, is why the tolerances in the standard are, at
> this stage, fairly... accommodating.
> The savings in productivity by 'simply' controlling the device through
> monitoring of the very well-known
> list of varibales, so that it's behaviour is always within a prescribed
> set of parameters (as described in
> the standard) is (or should be) the job of the press operators and
> those charged with their supervision.
Love your reasoning ;-)
You should post more often!
> Mark Stegman
> Teacher
> Graphic Prepress
> Sydney Institute
Roger
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