Process Work

[gordo]

I see your "Nooooooo!" and raise you....something.

I will SORT OF agree with you (given the respect I have for you, it would be foolish to completely disagree with you!).....this was sort of a long-standing debate in the G7 world early on...to linearize prior to determining tone curves or not. My "argument" for the case of applying a plate linearization curve prior to press curves is simply one of practicality.....when the G7 Curve software reports that my 50% dot should be a 46% dot, I want to be able to measure/verify that DIRECTLY on the plate and not have to go through mental gymnastics compensating for the non-linearity that the curve calculation software knows nothing about. Of course, if I could some how TELL IT what my "raw" plate curve actually looked like, giving it the ability to compensate for this and give me the actual on-plate value, I'd be OK with that....but for now the software I'm using assumes 50%=50% from the outset.

...and no disrespect intended.

You give me too much credit

I did not have a good experience when I was on the GRACoL committee when G7 was being formulated and that has colored my thinking about GRACoL 7/G7. So I do not know the subtleties of the G7 method, however in the 2009 "How To" there is this paragraph:

"E.4.2 Pre-Linearized or Un-Calibrated Plates?
It is important to note that G7 press calibration can either take the place of, or be applied in combination with, conventional plate linearization. If the G7 calibration run uses “un-calibrated” plates, the G7 correction values will take the place of conventional linearization curves. If the calibration run uses “pre-linearized” plates, the G7 correction values must be applied in combination with any linearization curves, with both curves working simultaneously."

And then:

"6.2 Origin of NPDC curves
To determine the 'natural' NPDC curves of commercial CtP-based printing, G7 research analyzed
numerous press runs made with ISO-standard ink and paper, and a variety of plate types imaged on
“un-calibrated” CtP systems (no RIP curves applied, not even to “linearize” the plate).

5.4 Set up the RIP
Set up the plate making RIP exactly as you would for a normal job, but clear out any values in the
current calibration table, or begin with a new, empty table. The first press run is best made with ‘un-
calibrated’ plates – i.e. no calibration values in the RIP.
IMPORTANT: Do NOT linearize the plate-setter so that measured dot values on plate exactly match
original file percentages. Contrary to common belief, this may reduce accuracy of subsequent steps. "

This seems confusing in the light of what you wrote about the G7 curve software.

best, gordo

 

[Alith7]

This seems confusing in the light of what you wrote about the G7 curve software.

it is especially confusing because the three statements contradict each other. the first says you can use either method, the second says it doesn't recommend linearizing the plates first, the third says DO NOT linearize.

I still think it's kicking yourself to NOT linearize your plates. I know it's RARE that the laser can go out of whack, but it CAN happen, and if you don't have the specialist's tools to diagnose, without linearizing first you could end up chasing your own tail trying to figure out what went wrong if colors are not printing accurately.

Gordo, don't get me wrong, your advice has always been very helpful, but I have to respectfully disagree.

 

[gordo]

[SNIP] I know it's RARE that the laser can go out of whack, but it CAN happen, and if you don't have the specialist's tools to diagnose, without linearizing first you could end up chasing your own tail trying to figure out what went wrong if colors are not printing accurately.

Gordo, don't get me wrong, your advice has always been very helpful, but I have to respectfully disagree.

Can you explain how not linearizing first would result in chasing your own tail trying to figure out what went wrong if colors are not printing accurately?

Or put another way - how linearizing first would results in being better able to figure out what went wrong if colors are not printing accurately?

best, gordo

 

[Lukas Engqvist]

As long as you document the result when the laser is in shape, you can easily verify that the laser still is in shape, by the simple fact that the result is consistent with the documented reference.
What Alith7 is saying is that the linearisation allows one adjustment curve to compensate for defects/change in the CTP. The G7 manuals are not contradicting, they are simply, in varying degrees saying that you can linearise, as long as you combine linearisation with other linearisation curves, but that this means a reduction in quality (because of 2 mathematical equations instead of one). There was a long discussion in a survey that Gordo did some time ago.

 

[gordo]

Thanks Lukas, but I'd still like to hear from Alith7 so that I can understand the thinking behind how not linearizing first would result in chasing your own tail trying to figure out what went wrong if colors are not printing accurately, or how linearizing first would result in being better able to figure out what went wrong if colors are not printing accurately.

best, gordo

 

[TerryWyse]

Thanks Lukas, but I'd still like to hear from Alith7 so that I can understand the thinking behind how not linearizing first would result in chasing your own tail trying to figure out what went wrong if colors are not printing accurately, or how linearizing first would result in being better able to figure out what went wrong if colors are not printing accurately.

I'm not "Alith7" obviously....but I think it's more about, if there is a problem where troublshooting is required, simply disabling your press adjustment curves and going back and imaging a "linear" plate to see if the plate imaging system has changed before starting to point fingers at either the pressroom or the plateroom.

Of course, if you've carefully documented the plate system in it's "non-llinear" or "raw" state and/or with the press compensation curves in place, you could troubleshoot the plate system without it being linearized....but it's a heck-of-a-lot simpler to have the plates linear to begin with as a starting or reference point.

The other point here would be if I've got multiple presses and multiple press curves (consider that quite often there's not a single adjustment for each press but likely unique C, M, Y and K curves for each press...multupled by the number of presses you may have), if the plate systems goes "off" for some reason, I have a single plate media linearization curve to correct or adjust to bring all my press curves back in "calibration"...but if I haven't linearized the plates I've no linearization "reference" point to get back to, I've now got to either adjust multiple press curves or possibly hire a technician to come in and see if the uncalibrated state of the original system can be brought back in tolerance.

The other similar case would be if I change plates or plating systems altogether, I at least a good chance of making things "printable" again by limply applying a plate media linearization curve to the new plates/system rather than be faced with the prospect of re-calibrating my entire pressroom again. Of course, with new/different plates, it likely will have to happen anyway (new press calibration) but getting back to linear before I have to face that would be a good starting point.

Terry

 

[gordo]

I was hoping to get a response from Alith7 so that I could understand his thinking behind his assertions rather than get into a general discussion about the topic.
The point, to me, is not so much about which method is correct or not, but instead about how one arrives at their conclusion. Is it a thought through opinion or is it an intuitive process.

That being said here's my response to Terry's post:

I'm not "Alith7" obviously....but I think it's more about, if there is a problem where troublshooting is required, simply disabling your press adjustment curves and going back and imaging a "linear" plate to see if the plate imaging system has changed before starting to point fingers at either the pressroom or the plateroom.

I don't see how applying a linearizing curve would be any different than applying a press adjustment curve in determining if the plate imaging system has changed. In both cases a single plate curve is applied - either a linearizing curve or a press curve. Then in one (your) case a press curve is applied on top of the linearizng curve.
In both cases the plate will have the same final specific tone values. If something has changed in the imaging system then it would show up in a change in the final tones on the plate.
Put another way, let's say that the unlinearized plate delivers a 43% when 50% is requested.
If the press requires a plate with a 57% dot at a requested 50% tone value then in your case I apply a curve to bring 43% to 50% and then another curve to bring 50% to 57%. In my workflow I would only apply a curve to bring 43% to 57%.
If there was a problem in the pressroom - both of us would have to check that a 50% request had resulted in 57% on the plate.
I don't see how you are any further ahead than me and you have introduced a second potential point of failure (i.e. was the linearizing curve applied)

Of course, if you've carefully documented the plate system in it's "non-llinear" or "raw" state and/or with the press compensation curves in place, you could troubleshoot the plate system without it being linearized....but it's a heck-of-a-lot simpler to have the plates linear to begin with as a starting or reference point.

Yes, in both cases the plate system needs to be documented in it's "non-llinear" or "raw" state and/or with the press compensation curves in place otherwise you cannot apply a linearizing curve, and I cannot apply a press curve (skipping the liniearizing curve). I don't see how that makes it a heck-of-a-lot simpler to have the plates linear to begin with as a starting or reference point.

The other point here would be if I've got multiple presses and multiple press curves (consider that quite often there's not a single adjustment for each press but likely unique C, M, Y and K curves for each press...multupled by the number of presses you may have), if the plate systems goes "off" for some reason, I have a single plate media linearization curve to correct or adjust to bring all my press curves back in "calibration"...but if I haven't linearized the plates I've no linearization "reference" point to get back to, I've now got to either adjust multiple press curves or possibly hire a technician to come in and see if the uncalibrated state of the original system can be brought back in tolerance.

In this case I would agree with you. I don't think that your example represents the vast majority of print shop situations, but if this was the case then it would seem to make sense to apply a linearizing curve first.

The other similar case would be if I change plates or plating systems altogether, I at least a good chance of making things "printable" again by limply applying a plate media linearization curve to the new plates/system rather than be faced with the prospect of re-calibrating my entire pressroom again. Of course, with new/different plates, it likely will have to happen anyway (new press calibration) but getting back to linear before I have to face that would be a good starting point.

You might simply modify your curves to achieve the same final tones on press. It's not a big complication or time consuming process. The shop that I worked at had two CtP devices and 10 presses. In addition to being a commercial print shop we were also a test facility for a CtP and a press vendor. We had no problem keeping everything in line without using linearizing curves prior to press curves.

best, gordo

 

[David Milisock]

Ok to play devils advocate here, if you don't run a linreaization or /test calibration of the plate setter how do you know that it's performing within parameters?

Same can be said about the press, if you don't observe the press work prior to attempting to calibrate how do you know if it's performing roperly befofre calibrating.

This may seem like BS to people who work in the shop they are calibrating but for us who walk into a shop blind so to say it's a big deal. It's easy to see press slur ina shop where you can walk by the press every day but to travel quite a while to fid out the press needs to schedule a repair before you can do your job is a bite.

Some shops are really just awful.

 

[gordo]

Ok to play devils advocate here, if you don't run a linreaization or /test calibration of the plate setter how do you know that it's performing within parameters?

Same can be said about the press, if you don't observe the press work prior to attempting to calibrate how do you know if it's performing roperly befofre calibrating.

[SNIP]

Linearization and calibration are two different functions.

In a CtP workflow the important thing is to set laser exposure and processing (or lack thereof) to the manufacturer's specifications so that the result is a robust halftone dot on the plate that maintains its integrity on press. That is what is done by the CtP vendor's engineer. That process is calibrating the CtP/plate imaging system. (same basic thing occurs in a film workflow).
However, once that calibration is done, the resulting plates are typically not linear due to the dynamics of laser exposure, individual plate characteristics, and processing.
From a CtP vendor engineer's perspective, it does not matter whether the result of their calibration setup is a linear plate or not since, from their point of view, a tone reproduction curve can always be applied to achieve whatever tones are required on plate or press.
Put another way - the key criteria is that when properly set up by the vendor - i.e. "calibrated" - the plate will probably have a characteristic non-linear tone response. And that's fine - as long as the plate responds the same, i.e. delivers the same non-linear tone response, every time because that imaging consistency makes it possible to build any tone reproduction curves that may be needed to achieve the desired presswork.

Regarding the press. Yes you need to observe the press work prior to attempting to calibrate so that you know if it's performing properly before calibrating. But you do not need to have linear plates in order to determine whether the press is performing properly or not.

best, gordo

 

[David Milisock]

Linearization and calibration are two different functions.

In a CtP workflow the important thing is to set laser exposure and processing (or lack thereof) to the manufacturer's specifications so that the result is a robust halftone dot on the plate that maintains its integrity on press. That is what is done by the CtP vendor's engineer. That process is calibrating the CtP/plate imaging system. (same basic thing occurs in a film workflow).
However, once that calibration is done, the resulting plates are typically not linear due to the dynamics of laser exposure, individual plate characteristics, and processing.
From a CtP vendor engineer's perspective, it does not matter whether the result of their calibration setup is a linear plate or not since, from their point of view, a tone reproduction curve can always be applied to achieve whatever tones are required on plate or press.
Put another way - the key criteria is that when properly set up by the vendor - i.e. "calibrated" - the plate will probably have a characteristic non-linear tone response. And that's fine - as long as the plate responds the same, i.e. delivers the same non-linear tone response, every time because that imaging consistency makes it possible to build any tone reproduction curves that may be needed to achieve the desired presswork.

Regarding the press. Yes you need to observe the press work prior to attempting to calibrate so that you know if it's performing properly before calibrating. But you do not need to have linear plates in order to determine whether the press is performing properly or not.

best, gordo

Many times you can be hired because the vendor has failed in their task, this can be the reason behind many consultant jobs.

Unfortunately many shops are in very poor shape due to their inability to recognize poor service from vendors and that includes many color management service providers. I was told by one CM profssional a couple years ago that the new reading device he was using was wonderful as he could read and calibrate the ink jet in a very short time. Unfortunately the media and inks he was calibrating by manufactures specification required 24 hours for the color to stabilize.

I agree regardless of the process ICC controlled or PS color managed the plate setter must respond to the same stimulus the same way every time.

You also do not need linear plates to test the press however you had better have some press experience as many pressmen today do not. I've been on site where they didn't know some of the ink fountian keys were malfunctioning and could not see a fountain solution imbalance.

We cannot esape the fact that the press is simply an linear analogous film generator and that the illusion of continous tone requires the linear consistancy of the dot pattern and the ink film density.

 

[Tarun Chopra]

It's interesting to know that we can operate without linearising our CtP devices but how can we justify using plate control tools like plate wedges eg plate wedge from ugra as visual control tools, I believe all control tools are based on presumption that you are imaging linear plates else they are all useless as control tools?

How can one expect similar results from a multiple CtP environment where both the devices are imaging different values?

Regards

 

[gordo]

It's interesting to know that we can operate without linearising our CtP devices but how can we justify using plate control tools like plate wedges eg plate wedge from ugra as visual control tools, I believe all control tools are based on presumption that you are imaging linear plates else they are all useless as control tools?

How can one expect similar results from a multiple CtP environment where both the devices are imaging different values?

Regards

AFAIK control tools, like UGRA, are not based on presumption that you are imaging linear plates.

In a CtP plate imaging system you are looking at two separate conditions.

1- proper exposure and development of the plate. That is to give you a robust image on the plate to accept ink as well as non-image areas that accept water but not ink. That is what the UGRA targets, as well as the vendor's targets are intended to do. This is what plate control wedges help you to validate. This is what your vendor's engineer does when they calibrate your system.

2 - The application of a tone reproduction curve that will create the required dots on plate that will result in the required tone reproduction on press. This is also what plate control wedges help you to validate.

Put another way - first the plate needs to be exposed and developed as specified by the manufacturer. Then a curve needs to be applied so that it delivers the required tone reproduction in the final presswork.

best, gordo

 

[Bondi_dan]

An UGRA Control Strip is a 1 bit tiff file with tint wedges and other tools to assist diagnostics on ctp plates.

It is not a pre-requisite to have a linear plate setter, it will show you what you are imaging so you can make the desired adjustments.

It is a worthwhile tool and it is customized with the name of the company that purchases it.

Regards,

Dan Wilson
G7 Expert
UGRA Expert Consultant
FTA Implementation Specialist

 

[Alith7]

I see what I get for not checking in for a few days...


Gordo~
Terry hit it right on the head. We have multiple different presses, plate thicknesses, and different stock (coated/uncoated) curves. Making sure that plates are "linear" before apply individual press curves gives me a quick reference point to check if something goes wrong.

Maybe it's just the CTP systems that we've had here, but the laser can occasionally shift. yes, it does have it's own built in calibration systems, but even those can miss if there is dust on the eye or any number of things. and usually, when the laser is off, it's in the low end or high end dots that it affects the most, not so much the 50%. In a perfect world, these systems should be cleaned and checked regularly, but the reality is that it doesn't happen as often as it should.

With that in mind, as Terry said, when curves aren't printing right, your general shop manager/pressman doesn't understand or give a flying flip about the intricacies of calibration curves. so, to avoid the finger pointing, the easiest place to start diagnosing the problem is to have an EASY to check baseline reference. Spend a quick 5 mins to burn a test strip on a plate, read the dots and prove that the CTP is burning linear, now you have shown the proof that the plates/curves are in line and you can move on to looking at the myriad of assorted press issues that could be causing the problem. to show that 100=100, 75=75, 50=50, 25=25 and all the rest is something anyone can understand.

To some it may sound like a redundant process, but if you spend any time working in a shop where everything is always prepress's fault, and the pressmen can do no wrong, it's kind of a no-brainer.

Also, if the laser is off, not everyone has the resources to get the CTP back in spec, or the time/money to fork over to fly in a tech to fix it. where as, if you can apply a new linear plate curve to bring it back into line, if nothing else to hold you over until the tech can get there so that you can keep running, without messing with all your other curves, why would you not put that kind of safe guard into your calibration system.

And Gordo HER thought processes are a combination of very thoroughly thought through and tried and tested conclusions, with adjustments made as new information is found/learned. Your idea that the vendor SHOULD have correctly calibrated and set-up the system on install is an honorable one, but not a realistic one. Also, the best set-up system isn't going to stay factory spec over years. Our current CTP has been in our shop for over 3 years now, I don't know of ANY machine, even if well maintained that will perform EXACTLY the same as it did new out of the box years down the road.

There were quite a few other reasons brought up by others that don't apply to my shop specifically, such as multiple CTP environments, that make sense also. The bottom line, the way I see it is this: you wouldn't use a Spectro or a Densitometer or a plate reader with out first checking to make sure that it is calibrated and reading correctly, the CTP is a tool just like they are, why wouldn't you calibrate it also to make sure that it is burning correctly before trying to adjust calibration curves on press? You try to make sure that a press is running as in spec as possible before you foot print it. Why would you not linearize the CTP and possibly throw a set of unknown and possibly erratic variables into your system?

Does that answer most of your concerns as to why I insist that you should linearize the CTP before calibrating press curves?

 

[gordo]

@Alith7

You know I had a funny feeling when I wrote "his" that it wasn't. LOL I usually try to be gender neutral -which is why I never write "pressman" - but I got lazy this time. And now you've added an Avatar - which makes it a bit clearer!

Gordo~
Terry hit it right on the head. We have multiple different presses, plate thicknesses, and different stock (coated/uncoated) curves. Making sure that plates are "linear" before apply individual press curves gives me a quick reference point to check if something goes wrong.

That's a lot of curves to manage. Maybe I'm misunderstanding you, but since you don't see the result of the linear curve because it gets clobbered by the press curve, I don't see how you can make sure that the plates are linear when you use a press curve. If you want linear patches to measure then you could simply impose a curved bitmap step wedge in the gripper margin that creates linear patches. That way you have linear patches if you want but still have the simplicity of a one curve workflow.

With that in mind, as Terry said, when curves aren't printing right, your general shop manager/pressman doesn't understand or give a flying flip about the intricacies of calibration curves. so, to avoid the finger pointing, the easiest place to start diagnosing the problem is to have an EASY to check baseline reference. Spend a quick 5 mins to burn a test strip on a plate, read the dots and prove that the CTP is burning linear, now you have shown the proof that the plates/curves are in line and you can move on to looking at the myriad of assorted press issues that could be causing the problem. to show that 100=100, 75=75, 50=50, 25=25 and all the rest is something anyone can understand.

If you do what you are saying you do then you do not need to apply a press curve on top of a linearizing curve in day to day production. Just use a press curve, and if there are any issues do what you say you do, burn the demonstration plate with a linearizing curve.
As an alternative, you could do what I suggested earlier - have a target in the gripper margin. The difference though is that if you include the linearized patch on every plate then there is no need to burn another plate to prove that that the CtP is burning linear.

A possible problem with showing the press people that the plate is burning linear is that it is not related to the dots they are using to print the job - i.e. the plate is actually not linear it has a curve applied to it. Telling them a fairy tale like that might result in them telling you some pressroom fairy tales if they take the attitude that your general prepress manager/operator doesn't understand or give a flying flip about the intricacies of the press curves.

To some it may sound like a redundant process, but if you spend any time working in a shop where everything is always prepress's fault, and the pressmen can do no wrong, it's kind of a no-brainer.

It sounds redundant because it is. It adds complication to the workflow without benefit. And in your case, as you've explained, you actually don't need the double curves workflow.
I've spent a lot of time in shops where everything is always prepress's fault, and the press operator's can do no wrong. It's not a healthy environment for either the employees or the company itself. IMHO, a more productive approach is education. It does work wonders and is a more sustainable strategy.

Also, if the laser is off, not everyone has the resources to get the CTP back in spec, or the time/money to fork over to fly in a tech to fix it. where as, if you can apply a new linear plate curve to bring it back into line, if nothing else to hold you over until the tech can get there so that you can keep running, without messing with all your other curves, why would you not put that kind of safe guard into your calibration system.

In my experience, using curves to fix a plate imaging problem does not work. So I don't see it as a safe guard.

And Gordo HER thought processes are a combination of very thoroughly thought through and tried and tested conclusions, with adjustments made as new information is found/learned.

That's what I was looking for - the thought processes. Unfortunately, in your case, I don't see your thought processes supporting the conclusion you've reached. But maybe I've not understood your examples correctly.

Your idea that the vendor SHOULD have correctly calibrated and set-up the system on install is an honorable one, but not a realistic one. Also, the best set-up system isn't going to stay factory spec over years. Our current CTP has been in our shop for over 3 years now, I don't know of ANY machine, even if well maintained that will perform EXACTLY the same as it did new out of the box years down the road.

I can only speak from what I've seen in hundreds of shops (and what a few vendors have claimed for their systems on this forum) is that the range of variation is within the "noise." I.e. The inherent variation doesn't require a change in curves. And if it's an imaging problem then curves will not fix it anyway.

The bottom line, the way I see it is this: you wouldn't use a Spectro or a Densitometer or a plate reader with out first checking to make sure that it is calibrated and reading correctly, the CTP is a tool just like they are, why wouldn't you calibrate it also to make sure that it is burning correctly before trying to adjust calibration curves on press?

This might be a difference in our terminology. In a CtP workflow the important thing is to set laser exposure and processing (or lack thereof) to the manufacturer's specifications so that the result is a robust halftone dot on the plate that maintains its integrity on press. That process is calibrating the CtP/plate imaging system. The result is a calibrated plate - it may not be linear, but it is calibrated.

You try to make sure that a press is running as in spec as possible before you foot print it. Why would you not linearize the CTP and possibly throw a set of unknown and possibly erratic variables into your system?

The tones on plate are there to create a desired tone response in the presswork.
Curving a plate to make it linear will result in a certain tone reproduction on press.
Curving a plate to make it linear and then curving the curve to result in a certain tone reproduction on press makes the linearizing curve redundant. Why not simply curve the plate once to achieve the desired tone reproduction on press?

You do not need a linear plate in order to determine that the press is in spec or not. When you test a press to see if it's in spec you are primarily testing for things like ink transfer since that is the primary function of the press and what the press is designed to do. The tone reproduction in the presswork gives you an insight into how well that ink transfer is occurring irrespective of whether the plate is linear or not.

Does that answer most of your concerns as to why I insist that you should linearize the CTP before calibrating press curves?

Yes and no as explained in my comments.

Thanks for responding - it's appreciated.

best, gordo

 

[Alith7]

Gordo~
no offense was taken, and you're certainly not the first to make the mistake.

it's rare in the print world (at least in my small portion of it) to come across women as it is, let alone women who speak up, or have a decent head on their shoulders, I finally added the avatar to clear some of that up. though it doesn't help much since now I look like a kid instead of 29 with 10 years experience!

I've got a mess on my desk atm, but I will address some of your points later, I'm self taught, so a lot of my knowledge is piece-meal and a bit unconventional, though it tends to work. I want to take a bit tonight and read through your comments thoroughly instead of a quick skim so I can see your point of view (which may be right), and fit the pieces into what I "know". Like I said pages ago, I respect your opinion and have often gotten new knowledge and insight from your posts so I want to make sure I've got all this.

 

[Alith7]

OH! and I usually write "pressMAN"....man or woman, they generally tend be as pig headed as your general man...

 

[Tarun Chopra]

There is an area in the control tool "visual reference steps" this is used to verify if the plate is imaged linear. I have also seen other tools that have bitmapped screen values on top at 10% steps with vector values on bottom which when imaged should be equal to the bitmapped values such control tools are based on fact that the imaging devices are linear.

I have heard that violet CtP systems have to be linearised in a daily basis (or maybe 2~3 days) a technological limitation of the process as I understand based on the inputs. Companies using such system will have to linearise the devices as and when required. How would they establish consistent working conditions under such circumstances?

Regards

 

[David Milisock]

I see what I get for not checking in for a few days...


Gordo~
Terry hit it right on the head. We have multiple different presses, plate thicknesses, and different stock (coated/uncoated) curves. Making sure that plates are "linear" before apply individual press curves gives me a quick reference point to check if something goes wrong.

Maybe it's just the CTP systems that we've had here, but the laser can occasionally shift. yes, it does have it's own built in calibration systems, but even those can miss if there is dust on the eye or any number of things. and usually, when the laser is off, it's in the low end or high end dots that it affects the most, not so much the 50%. In a perfect world, these systems should be cleaned and checked regularly, but the reality is that it doesn't happen as often as it should.

With that in mind, as Terry said, when curves aren't printing right, your general shop manager/pressman doesn't understand or give a flying flip about the intricacies of calibration curves. so, to avoid the finger pointing, the easiest place to start diagnosing the problem is to have an EASY to check baseline reference. Spend a quick 5 mins to burn a test strip on a plate, read the dots and prove that the CTP is burning linear, now you have shown the proof that the plates/curves are in line and you can move on to looking at the myriad of assorted press issues that could be causing the problem. to show that 100=100, 75=75, 50=50, 25=25 and all the rest is something anyone can understand.

To some it may sound like a redundant process, but if you spend any time working in a shop where everything is always prepress's fault, and the pressmen can do no wrong, it's kind of a no-brainer.

Also, if the laser is off, not everyone has the resources to get the CTP back in spec, or the time/money to fork over to fly in a tech to fix it. where as, if you can apply a new linear plate curve to bring it back into line, if nothing else to hold you over until the tech can get there so that you can keep running, without messing with all your other curves, why would you not put that kind of safe guard into your calibration system.

And Gordo HER thought processes are a combination of very thoroughly thought through and tried and tested conclusions, with adjustments made as new information is found/learned. Your idea that the vendor SHOULD have correctly calibrated and set-up the system on install is an honorable one, but not a realistic one. Also, the best set-up system isn't going to stay factory spec over years. Our current CTP has been in our shop for over 3 years now, I don't know of ANY machine, even if well maintained that will perform EXACTLY the same as it did new out of the box years down the road.

There were quite a few other reasons brought up by others that don't apply to my shop specifically, such as multiple CTP environments, that make sense also. The bottom line, the way I see it is this: you wouldn't use a Spectro or a Densitometer or a plate reader with out first checking to make sure that it is calibrated and reading correctly, the CTP is a tool just like they are, why wouldn't you calibrate it also to make sure that it is burning correctly before trying to adjust calibration curves on press? You try to make sure that a press is running as in spec as possible before you foot print it. Why would you not linearize the CTP and possibly throw a set of unknown and possibly erratic variables into your system?

Does that answer most of your concerns as to why I insist that you should linearize the CTP before calibrating press curves?

>Making sure that plates are "linear" before apply individual press curves gives me a quick reference point to check if something goes wrong.
>so, to avoid the finger pointing, the easiest place to start diagnosing the problem is to have an EASY to check baseline reference. Spend a quick 5 mins to burn a test strip on a plate, read the dots and prove that the CTP is burning linear, now you have shown the proof that the plates/curves are in line and you can move on to looking at the myriad of assorted press issues that could be causing the problem. to show that 100=100, 75=75, 50=50, 25=25 and all the rest is something anyone can understand.

You're a man after my own heart!! No offence intended.

 

[gordo]

There is an area in the control tool "visual reference steps" this is used to verify if the plate is imaged linear. I have also seen other tools that have bitmapped screen values on top at 10% steps with vector values on bottom which when imaged should be equal to the bitmapped values such control tools are based on fact that the imaging devices are linear.

Do you have the name of such a control tool? I don't know of any that are specifically designed to verify if the plate is imaged linear since that isn't important.
Generally the control tool that has bitmapped screen values above and vector tone values below are used to verify that the correct tone reproduction curve was applied. It is not based on whether the plate is imaged linear or not.
The bitmapped image was created with a curve applied and the vector art picks up the curve when it is RIPped. If you can't see a difference in the tones then that confirms that the right curve was applied. It's explained in more detail here: Quality In Print: Confirming the Applied Calibration Plate Curve - without measuring the plate

Perhaps someone can explain about calibrating and/or linearizing violet devices. I don't have enough experience to comment.

best, gordo