Is linear plates more important that backward compatibility with TVI curves?

[Lukas Engqvist]

Some will understand where the question comes from, but wanted to ask the community as a whole.

When targeting ISO or eg FOGRA 39 do you have linear CTP plates? Is it important? Are you able to hit the target TVI curves on paper? If you are having problems to get the TVI for FOGRA 39, would be interesting to know if a linear plate would be a better target for your workflow. If you had a linear plate what would be the ink coverage area of a 50% dot on plate once it came was printed.

A related question is of course what lpi are you ripping to?

Oh and one more question… do you know how to contact your national representative in the ISO technical groups (if you wanted to)?

 

[gordo]

Constraining the standard to linear plates is idiotic. Nobody cares, or should care, about what the tones are on the plate. What's important are the requested tones in the file and the measured tones in the press work. The standard should identify the target press work tone reproduction (as it does the ink hues) and the printer should hit that tone reproduction curve by whatever means they choose. Ideally there would be only one target press curve irregardless of lpi, screening process, or, perhaps print process. One press tone curve to rule them all.
That would create a standard for print tone reproduction.

Best, gordo

 

[chevalier]

Linearizing plates is a pointless exercise. However, one should always verify that plates are being consistently imaged and developed. If your CtP+OLP aren't consistently imaging and developing plates you are screwed. We check a set of plates twice a week and every plate gets a control strip on it. If it were offered in an affordable and automated fashion I would push to have a control strip on every plate checked. If there are print abnormalities we can quickly identify/eliminate prepress and plating variables. We verify and log everything which has virtually eliminated press downtime, inaccuracies and inconsistency due to prepress.

 

[gordo]

Linearizing plates is a pointless exercise. However, one should always verify that plates are being consistently imaged and developed.

Bingo!

best, gordo

 

[ansoft]

In my opinion the plates should be linearized. It is easier to define where the problems come- from prepress, from ctp, or from the press. Otherwise we are in Catch 22- everybody says the problem is not in my machine.

 

[gordo]

In my opinion the plates should be linearized. It is easier to define where the problems come- from prepress, from ctp, or from the press. Otherwise we are in Catch 22- everybody says the problem is not in my machine.

Not true. Prepress sends plates with certain tone values to the press room. It does not matter whether the tone values are linear or not. What matters is the the tone values are consistent. If the plate measures the same (but not linear) as it did a month ago then any problem is likely not the plate but the press.

Also, if you say that plates should be linear irrespective of lpi, halftone screen type, process, or substrate then you will have poor alignment between print processes. You will also make certain screen types impossible to conform ( e.g. FM, high lpi AM/xm etc.) to any standard.


Best, grdo

 

[Green Printer]

Not true. Prepress sends plates with certain tone values to the press room. It does not matter whether the tone values are linear or not. What matters is the the tone values are consistent. If the plate measures the same (but not linear) as it did a month ago then any problem is likely not the plate but the press.

Also, if you say that plates should be linear irrespective of lpi, halftone screen type, process, or substrate then you will have poor alignment between print processes. You will also make certain screen types impossible to conform ( e.g. FM, high lpi AM/xm etc.) to any standard.


Best, grdo

Gordo I agree with you 100%. AS long as your plate is properly calibrated to hold the smallest dot you need every thing always falls in place. Have an exposure wedge in the gripper or tail of every plate and you will always know where you are at. With a correctly made curve if you must change exposure it doesn't matter the curve will move along with the exposure change to hold your smallest dot. We have been doing this with CTP since 1998 and never have had a curve problem

 

[Ozkan Hangisi]

Only dot gain score on printed material is important. Most of time linerazition makes no sense. If plate causes huge dot gain on press with correct exposure (it can be negative plate) then pre-bending curve can help for smoothness on darker areas. Linerazition curve or any curve which pulls dot areas down on plate can be used as base for process calibration test.

Regards
Ozkan

 

[mglouis]

Lukas,

I have never made PSO or G7 curves from a non-linear plate. It's hard to imagine a 50% dot being harder to control one way or the other. Currently I am not able to identify problems related to using linear plates, however in the past, when using a Fuji Saber (violet) I used to get strange negative dot gain in the highlights after a G7 set-up, particularly in the black channel; I never diagnosed the cause of that but always felt it was related to plate linearization. We print at 175 lpi. As a Rampage user I must use 25 fulcrum points so after setting up one CTP device and one press (lin+c+m+y+k) I am using 125 fulcrum points.

I understand the math simplicity argument for uncalibrated plates, however, a case can be made for whatever conditions require the least amount of correction would be best. Because I maintain curves for 4 platesetters and 14 curve sets and cannot identify a quality compromise with linear plates, my preference is for linear plates; otherwise I would have (4*14) 56 tone curves (or [56*25] 1400 fulcrum points) and each time I updated one set I would have to update three more.

In the US I would contact someone in the IDEAlliance Print Properties group who serves as a technical committee for ISO input for the print stuff.

Matt Louis

 

[Green Printer]

Why worry about a 50% dot. You can swing an exposure on some ctp unit plus or minus 25% of exposure settings and still hold a perfect 50% dot while the highlights and shadows go to pot.

 

[gordo]

Lukas,

I have never made PSO or G7 curves from a non-linear plate. It's hard to imagine a 50% dot being harder to control one way or the other. Currently I am not able to identify problems related to using linear plates, however in the past, when using a Fuji Saber (violet) I used to get strange negative dot gain in the highlights after a G7 set-up, particularly in the black channel; I never diagnosed the cause of that but always felt it was related to plate linearization. We print at 175 lpi. As a Rampage user I must use 25 fulcrum points so after setting up one CTP device and one press (lin+c+m+y+k) I am using 125 fulcrum points.

I understand the math simplicity argument for uncalibrated plates, however, a case can be made for whatever conditions require the least amount of correction would be best. Because I maintain curves for 4 platesetters and 14 curve sets and cannot identify a quality compromise with linear plates, my preference is for linear plates; otherwise I would have (4*14) 56 tone curves (or [56*25] 1400 fulcrum points) and each time I updated one set I would have to update three more.

In the US I would contact someone in the IDEAlliance Print Properties group who serves as a technical committee for ISO input for the print stuff.

Matt Louis

As a general statement, at 175 lpi - linear plates will give you a result that is very close to traditional sheetfed offset tone reproduction (i.e. dot gain). So the curve to make the plate linear from its natural state in effect is a dot gain compensation curve. The curve doesn't have to make the plate linear but in the case of 175 lpi it so happens that that is the appropriate curve. However, if you change screening (e.g. use FM or higher or lower lpi AM/XM) or use a different substrate, then linear plates will not give you the correct tone reproduction (i.e. too much dot gain). In that case, you will need to create a plate curve that will result in the correct tone reproduction in your presswork. Your plates will no longer be linear.

The problem with arbitrarily using linear plates is that you cannot normalize tone reproduction across different screening technologies or substrates. If the goal for a standards organization is to normalize tone reproduction then there should be just one presswork tone curve that all printers should strive to achieve using whatever curves are needed to do so.

PS in a CtP workflow, calibrating plates is not making them linear. Calibrating the plate means adjusting exposure and processing in order to achieve a consistent, robust, image on the plate that will carry ink where needed and not where not needed. Once the plate is calibrated then a curve may be applied in order to achieve the required tone reproduction on press. That curve may or may not make the plate linear.

best, gordo

 

[mglouis]

Green Printer,

The 50 patch was the example used to initiate discussion. It's kind of a big deal on press But I understand your point. Being 2% off in a highlight is a bigger problem than in the mid-tone.

Our Fuji techs aren't really into tweaking exposure for the sake of hitting a 50% dot -- something something about laser life. We agreed to let them do their thing as we do ours. In any case, unless every CTP device has the same native curve then press tone management increases in complexity with each additional device.

If I may echo @chevalier, stability is king.

- Matt Louis

 

[mglouis]

Gordo,

Your statement supports IDEAlliances's claim that the reference NPDC shape was based on uncalibrated CTP (for 175 lpi). I would like to see ISO12647-2 adopt G7 NPDC and substrate relatively for gray balance and ink solids + overprints then let printers lean on FOGRA, IDEAlliance or whomever for print specifications as often as suitable. This relativity part should prevent ISO documents for graphic arts from becoming outdated as quickly as they have in the past.

Matt Louis

 

[gordo]

Gordo,

Your statement supports IDEAlliances's claim that the reference NPDC shape was based on uncalibrated CTP (for 175 lpi). [SNIP]

Matt Louis

The CTPs were calibrated (Creo Trendsetters). No curve was applied to make them linear (at least, AFAIK, after the first run at LA Graphico). However, the Creo Trendsetter/plate combinations that were used happen to result in virtually linear plates. Not all CtP/plate combinations do so.

best, gordo

 

[Paul Santer]

When a printing plate is developed, how should it respond to optimum CTP and processor settings from a linear file?

 

[Tommyjt]

Why shouldn't one linearize plates first? I recall two particular scenarios where it has been a benefit. One was when Kodak changed our plate processor developer temperature and developing time. That changed our dot on plates. The other was when they changed the laser intensity and that also changed the dot. In these two cases all I had to do was change the linearization curve and we were ready to roll.
To see those whom I have respect for call this "idiotic" makes me wonder if I'm missing something here.
Convince me that it is "pointless."

Regards

 

[gordo]

Why shouldn't one linearize plates first? I recall two particular scenarios where it has been a benefit. One was when Kodak changed our plate processor developer temperature and developing time. That changed our dot on plates. The other was when they changed the laser intensity and that also changed the dot. In these two cases all I had to do was change the linearization curve and we were ready to roll.
To see those whom I have respect for call this "idiotic" makes me wonder if I'm missing something here.
Convince me that it is "pointless."

Regards

OK, to use your example: "In these two cases all I had to do was change the linearization curve and we were ready to roll."

Correct. But if you didn't use a linearizing curve first then you could have written:
"In these two cases all I had to do was change the plate curve and we were ready to roll"

Using two curves, one to linearize and another to get the right tones on press doesn't gain you anything but complexity, a greater chance of making a mistake, as well as the potential for banding/shade stepping.
I'll grant that in a few cases, doing a linearization first is the way to go. However for the vast majority of printshops that step is redundant.

Best, gordo

 

[Ozkan Hangisi]

Why shouldn't one linearize plates first? I recall two particular scenarios where it has been a benefit. One was when Kodak changed our plate processor developer temperature and developing time. That changed our dot on plates. The other was when they changed the laser intensity and that also changed the dot. In these two cases all I had to do was change the linearization curve and we were ready to roll.
To see those whom I have respect for call this "idiotic" makes me wonder if I'm missing something here.

Convince me that it is "pointless."

Regards

Let me try acording to your scenarios Your dot gains were in tolerance. Then you changed developer parameters or laser power etc. Why do you think re-linerazition will provide same dot gains on the print ? You changed surface&emission referance of plate. It effects ink-water balance, dot endurance etc. After such scenarios, I would check just dot gains on print then modify print curves if necessery. Using lineraziton curve provides no advantage in you cases.

 

[BillJ]

I only linearize on systems that are being used for non-color managed shops. I learned long ago that applying multiple curves will make you chase your tail.

 

[Ozkan Hangisi]

I only linearize on systems that are being used for non-color managed shops. I learned long ago that applying multiple curves will make you chase your tail.

It is not chasing tail but standart. On the otherhand working with lineer plates is not that bad, as long as sky is blue, tree is green, repeat jobs are stable and none of your customers is asking for print standart.

Regards
Ozkan