Altering Press Curves
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gordo
Well-known member
On a side bar...the press curves are not usually the problem. Just saying.
J
johnny_jay
Guest
We do at least annually for our G7 certification. Sometimes we will fingerprint again if we see something or if a change is made in ink, blankets, etch, etc.
John Stewart
John Stewart
Gordo I so agree with you! So what kind of response do I give these press room guys who come running right to Prepress to see if A) a wrong curve was applied, or B) can we adjust to fix the problem? Rarely do we ever adjust the curve, but when we do it's just a bandaid to get them through a rush order.
It's all too common.
It's all too common.
gordo
Well-known member
I think it's great that they would come to prepress for help rather than try and sort it themselves (typically in secret).
Specifically to:
A) Your plates should always have a QC plate curves target in the gripper margin. A screened bilevel step wedge (that has had the curve applied) above butted to a continuous tone step wedge below. The screened wedge doesn't get affected by the RIP. If the correct curve has been applied to the contone wedge as it went through the RIP then visually you shouldn't see where they are abutted and so you know without measuring if the correct curve has been applied.
B) Usually the job needs to get done - so whatever it takes to do that should be done. However, time has to be taken to understand why the job had a problem.
However, from a print production business perspective it's always helpful to learn the cause when mistakes happen since it can reveal what needs to be improved in the production process.
The three most common ways people make errors are:
Perception-based. These occur when there is incomplete or ambiguous information. For example: “We need a quote on a four-page folder” could mean many different things. Perception-based errors can be avoided by providing clear and distinctive instructions, standardizing instructions, and avoiding assumptions intended to fill in missing information.
Decision-based. These occur because of stress, pre-existing biases, assumptions, and over-confidence. This type of error can be avoided by using checklists, decision trees, and go-no-go flow charts.
Knowledge-based. These occur due to a lack of knowledge, information, and/or poor communication. These can be avoided by standardizing terms and operational conventions as well as through formal training.
Determining and documenting the source of mistakes, or in this case a problem that manifested in the pressroom, helps clarify whether issues are random, intermittent, systemic, or trending in some way. This clarification informs your decisions moving forward.
IMHO, a print shop shouldn't be thinking in the terms of the OP - "How often are most people adjusting their press curves, especially those targeting GRACoL using G7" Instead they should be thinking in terms of a systematic way of objectively monitoring their print manufacturing process and creating the methodologies to maintain the process as much as possible in a steady state. So, for example, it doesn't drift out of G7 conformance (if that's the goal) over the course of a year (the case in many shops). Instead, it remains in conformance over the year.
fletcher0854
Member
Gordo,
Thank you for this insight. This is some very useful information for not only the current subject, but for every day procedures.
Thank you for this insight. This is some very useful information for not only the current subject, but for every day procedures.
prepressdork
Well-known member
We alter our press curves once a year for our G7 recertification. I adjust (if needed) linearization curves monthly to ensure linear plates are being imaged before our G7 curves are factored in.
pd
pd
gordo
Well-known member
I'm sure I'm misreading what you're saying. It reads that you only print to G7 once a year - when you apply for G7 recertification since that is when you alter your press curves to get into conformance. That's like saying you only do the speed limit in your car when there's a police radar speed trap set up.
Doubling up on curves (linearizing then G7) is a whole other can of worms.
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kansasquaker
Well-known member
LOL, don't ever try to have that conversation with somebody from Fuji. They made me sign a form saying they couldn't guarantee we'd get certified by idealliance unless we linearized our plates. Why bother trying to understand what you're doing and why? It's so much simpler to follow a check list and not do any independent thinking . . .
gordo
Well-known member
Since that doesn't make any sense then it must be correct!
I guess my question was geared more towards "are people realistically maintaining G7 standards for long periods of time, like between annual recertification?"
Our press color bars can be scanned in a database and the results for dot gain and grey balance be tended. and what we've noticed is that after about a few weeks from a retarget to GRACoL we tend to drift especially in grey balance. Our solid colors are almost always in spec by just achieving standard SID on press.
I'm just curious if that's normal because what it seems like we do is just correct a certain press condition when we make our G7 curves and when that press condition changes then we drift from our standards....it's frustrating and I'm hoping to gain some insight.
Also, Gordo, why do you hate make plate linearization curves so much
Our press color bars can be scanned in a database and the results for dot gain and grey balance be tended. and what we've noticed is that after about a few weeks from a retarget to GRACoL we tend to drift especially in grey balance. Our solid colors are almost always in spec by just achieving standard SID on press.
I'm just curious if that's normal because what it seems like we do is just correct a certain press condition when we make our G7 curves and when that press condition changes then we drift from our standards....it's frustrating and I'm hoping to gain some insight.
Also, Gordo, why do you hate make plate linearization curves so much
gordo
Well-known member
I guess my question was geared more towards "are people realistically maintaining G7 standards for long periods of time, like between annual recertification?"
Our press color bars can be scanned in a database and the results for dot gain and grey balance be tended. and what we've noticed is that after about a few weeks from a retarget to GRACoL we tend to drift especially in grey balance. Our solid colors are almost always in spec by just achieving standard SID on press.
I'm just curious if that's normal because what it seems like we do is just correct a certain press condition when we make our G7 curves and when that press condition changes then we drift from our standards....it's frustrating and I'm hoping to gain some insight.
Also, Gordo, why do you hate make plate linearization curves so much
I hate plate linearization curves so much because, in the vast majority of cases, they are redundant in a CtP workflow. They also introduce an unneeded point of failure and can introduce artifacts like shadestepping. I explain it in depth here: http://the-print-guide.blogspot.ca/2...es-or-not.html
While we're on the hate issue...IMHO (and experience) grey balance is great for setting up a press (even if you use G7) however grey balance as reported by a color bar in production printing is a fantasy. I explain why here: http://the-print-guide.blogspot.ca/2...onvenient.html
System Brunner - the father of grey balance as a metric - also agrees but for different reasons as he did not believe in colormetric grey balance (which is what you're told to do) but in densitometric balance.
Here are his words**:
"Offset printing, with its standardized process colors CMYK, densitometry, and halftone area measurement, has created its own color space and an independent diagnostic and process technology that permits every phase of the printing process to be completely explainable and controllable. Which is why densitometry is infinitely more important than colorimetry for offset printing,
Colorimetry is absolutely unsuitable for controlling the printing process and detecting process faults in illustration printing."
Much, if not most, of the grey balance rhetoric is based on opinion, calls to authority, "just trust me thinking", and if it applies to scanners it must apply to printing presses - there's no objective quantitative published research to back any of it up.
I was a member of the idealliance group during the development and "testing" of G7 and attended about 5 of the press runs - what I saw caused me to to quit as I didn't want to be associated with how they were doing what they were doing.
So, I would consider your experience (grey balance in color bar in production work) as quite reasonable.
Oh, and while I'm ranting, idealliance initially sold G7 press sheets as representative targets/examples for printshops. But they quickly stopped doing so because, as I was told, the couldn't maintain G7/GRACoL7 conformance. Hmmmmm.
** Brunner quote extracted from:
Using colorimetry for ink regulation?
System Brunner replies to Heidelberg
In the magazine “Deutscher Drucker” no. 13 from April 25, 2003, Jürgen Mittmann, head of Product Management Prinect at Heidelberg, promoted colorimetry for inking unit regulation and positioned it as the superior technology. The populistic assertion that colorimetry perceives color like the human eye is bound to lead many printers astray.
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gordo
Well-known member
I make a distinction between setting up a press to meet a standard/specification vs running a press for production printing. These are two very different situations with very different goals and constraints.
In the steam-powered days of film - what ISO 12647 - n was based on, the film output standard was linear. Grey balance was poorly defined but it was the target when setting up a press to the standard.
In such a scenario the CMYK TVI gain curves had characteristic shapes, positions, and nesting according the the SIDs they were printed at and the assumption was that if you followed the ISO specifications for inks, TVIs, substrates, etc. you would hit the standard and BTW achieve the grey balance goal (measured in Lab if you could or eyeball if you couldn't).
It was one of the reasons why G7 was laughed at when originally presented to the ISO committee. They saw G7 as redundant and therefore not needed.
AFAIK the ISO 12647-2 was never (and never since) tested by Idealliance when G7 was proposed as a method for grey balancing a press.
On a sidebar, personally I would prefer colorimetric tone reproduction using Isometric curves - a.k.a. brown balance - as a better way to set up a press and for press control (in part because, unlike grey balance, it's objective and instrument-based) but AFAIK this was never explored by the committee. For more info Google "A Regression-Based Model of Colorimetric Tone Reproduction for Use in Print Standards"
Basically my issue is that if you're going to propose a new methodology (e.g. G7) you should first demonstrate that the current methodology (ISO 12647 and assoviated specifications) is flawed. Then demonstrate that the new methodology solves the issues embodied in the old methodology. AFAIK that was never done. You should also differentiate between setting up a system to a standard vs running production presswork. In one of the posts that I earlier pointed to I described why the grey balance patch in the color bar of a production press sheet has virtually no value. AFAIK, no one has ever actually tested validity of the colorimetric relationship of the grey balance patch in the color bar of a production press sheet. There is an assumption that it's meaningful but no research in such a basic subject has been done. Instead, how scanners and digital cameras operate are given as the models of why it should be so on a printing press. I would be very happy to be proven wrong on this.
While there appears to be a lot of science being applied to the print manufacturing process, if you actually start digging into it you quickly see that there's not much there at all.
I hope that clarifies things.
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D
Deleted member 16349
Guest
True, the science is pretty poor. What is worse is the lack of the ability to use basic Logic and also even simple Common Sense. Add to that the unbelievable ability to forget facts or to just ignore the them as if they don't matter.
The result has been an industry that is not capable of developing practical solutions to problems, that are easy, effective and straight forward for users.
I won't go on because it is just too frustrating to discuss it. So much potential but with so much lack of opportunity.
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