Color Management without Linearization

[RodrigoRocha]

Hello there!

I'd like to know what would be the issues on calibrating my Offset Printer only through testform comparison, without reading the plate and making the linearization of them. (Of course, consider that I'll maintain the plate supplier the same).

Also, I'd like to know if there is a spectro, like from x-rite or Techkon that reads both Plate (processless) and Printed Paper.

Thank you guys!

 

[gordo]

Hello there!

I'd like to know what would be the issues on calibrating my Offset Printer only through testform comparison, without reading the plate and making the linearization of them. (Of course, consider that I'll maintain the plate supplier the same).

Also, I'd like to know if there is a spectro, like from x-rite or Techkon that reads both Plate (processless) and Printed Paper.

Thank you guys!

You (like most CtP installations) don't need to linearize the plates.
Calibration (not linearization) is done by the engineer that sets up your CtP device. (Calibration=putting it into a defined state of exposure/processing)
You need to have target tone reproduction values for the presswork (e.g. the file requests 50% and I expect to read 68% in the presswork)
You image the file with its requested tone values to plate.
You run the plates at your selected solid ink densities.
You measure the tones in the presswork.
You build a tone reproduction curve that remaps the tones that will be imaged on plate so that you get the tones in the presswork that you expect.

More detailed info is here:
The Print Guide: To linearize your CtP plates or not?
and here:
The Print Guide: The principle of dot gain compensation plate curves

Color management is a whole other issue.

 

[cementary]

X-rite eXact reads both plates and paper

 

[chevalier]

Unless you have multiple CtP devices you do not need to linearize.

 

[gordo]

Unless you have multiple CtP devices you do not need to linearize.

I think that would depend on what brand/type of CtP you're using.

 

[motormount]

First let's clarify this one:

Linearization is measuring the plates if file values are equal to plate values,right?

Then calibration is measuring the sheet if printed values are equal to some standard,like for eci v2 300,a 50% cyan patch should be measured printed to paper type 2 for example to something like 65% - regardless if the plate was linearized or not -.

If not,lets's say is measured at 70%,we build a curve to compensate for that difference and theoretically we are good to go.

-At least that's what i've known-understood.-

So if anyone -like where i work- is changing plates every now and then,then to me sounds easier to change only the linearization curve and keep the calibration curve,than having to recalibrate wasting more time and sheets as well.

That's unless i'm wrong on my perception what linearization and calibration stands for,which unfortunately i'm not quite sure of even though i've read Gordo's articles more than once...

 

[chevalier]

I think that would depend on what brand/type of CtP you're using.

Willing to elaborate on this?

I think that you're implying if you have multiple identical PTRs for example of the same vintage that this is overkill.
The universal "it depends" certainly applies. I steadfastly believe in (somewhat redundant) linearization for multiple devices even if they devices are "identical".

 

[chevalier]

@motormount

I'm having a hard time understanding what you're saying.

Boiled down to absolute basics it works like this (I'm going to gloss over a lot):
Every CtP doesn't image the same
A CtP will have (pick your chosen term: TVI - tonal value increase, TVD - tonal value decrease, Dot gain, Dot loss). When you tell it to image 50% on a plate it may image 45% or 55%.
This is where linearization comes in (if you wish). You setup a curve to make the CtP image 50% when you tell it to image 50%.

Every press doesn't print the same
A press will have (pick your chosen term: TVI - tonal value increase, TVD - tonal value decrease, Dot gain, Dot loss). When you hang a plate with a 50% image it may print 45% or 55%.
Option A:
An unlinearized plate is put in the press, sheets are printed and screens measured for TVI. Corrective curves and created. Those curve corrections will account for the CtP's TVI and the printing press' TVI.
Option B:
A linearized plate is put in the press, sheets are printed and screens measured for TVI. Corrective curves and created. Those curve corrections will account for ONLY the printing press' TVI.

To linearize or not to linearize?
If you have one plate manufacturer (who is consistent), and one CtP device (that is consistent and well maintained) and one plate processor (that is consistent and well maintained [given that you aren't using process-free plates]) linearization is not necessary. You should be spot checking or checking all plates to verify consistency. We check every 20th job with a plate scope and have control (uncurved) strips and curved strips on the plate. We are also religious about maintenance.

If you have multiple CtP devices that are "identical" you should probably linearize. (My opinion: you must linearize. I don't believe in identical)
If you have multiple CtP devices that are not "identical" you must linearize - UNLESS each CtP only serves one press and meets all the criteria in the paragraph above. (My opinion: you must linearize. There will probably come a day when one machine is down and use the other one as a backup.)
If you have multiple plate vendors you MUST linearize. (Why would you have multiple vendors?!?)
If you have multiple plate processors you should probably linearize. (My opinion: you must linearize.)

 

[gordo]

Just to pile on to what chevalier wrote different (wording may help to make sure it's clear):

First let's clarify this one:

Linearization is measuring the plates if file values are equal to plate values,right?

Linearizing the plates is applying a tone reproduction curve to the plates so that the tones on the plates are equal to the tones specified in the source file. i.e. a 50% tone specified in the file results in a 50% tone measured on the plate. This is not calibration - it is linearization.

Then calibration is measuring the sheet if printed values are equal to some standard,like for eci v2 300,a 50% cyan patch should be measured printed to paper type 2 for example to something like 65% - regardless if the plate was linearized or not -.

If not,lets's say is measured at 70%,we build a curve to compensate for that difference and theoretically we are good to go.

Basically yes but I don't think I'd call it calibration. What you're doing is aligning the press tone response to a target using tone reproduction curves in the RIP. The target could be an industry standard or it could be a house standard. The linearity of the plates is not relevant.


When a CtP system is installed it is calibrated by the vendor's engineer to deliver a robust image on the plate with a clear non-imaging background. The result may or may not be a linear plate. Different plates and CtP combinations will all have their own characteristic plate tone response once the system is calibrated.

The resulting plates are put on the press and will deliver a tone response (a.k.a current curve) once the press is running at optimum ink film thickness (solid ink density).

That press tone response is then compared to the target (industry or shop standard) and if different, then a tone reproduction curve is calculated to alter the tones image on plates so that the press tone response aligns with the target.

The important thing is that the plates coming out of the processor are consistent.

So if anyone -like where i work- is changing plates every now and then,then to me sounds easier to change only the linearization curve and keep the calibration curve,than having to recalibrate wasting more time and sheets as well.

That's unless i'm wrong on my perception what linearization and calibration stands for,which unfortunately i'm not quite sure of even though i've read Gordo's articles more than once...

If the tone response on press later changes - you need to find out why before you think of creating curves to fix a press problem.
If the tone response on plate later changes - you need to find out why before you think of creating curves to fix a plate imaging problem. That being said the work to build a new plate tone reproduction curve is the same as to build a new linearization curve. They are, after all, both plate tone reproduction curves.

 

[johnny_jay]

We have two identical Agfa plate setters and do not linearize. When the machines were first set up we added an Agfa wedge. The wedge is lineart and is not affected with the press curve applied.

The 50% screen reads 52% when read with our Techkon SpectroPlate. We check 2 plates per shift from each platesetter, the measurement is recorded. The allowable tolerance is +/- 2% but to be honest, it is never a full 1% off.

The wedge also contains a visual reference as well.

One thought on changing plates and only changing the linerazation, I have been told from plate vendors and pressroom personnel that positive and negative plates will differ how they will print. Our pressroom manager prefers a positive plate over a negative one.


John

 

[motormount]

@chevalier

Reading the thread,and gordo's links afterwards,i had the question if in my case the two curves policy was a better than one.

Really sorry for jumping in,i should open another thread and thank very much you for your answer.

@gordo

On the linearization thing,i was meaning the same,even not put down in words as clearly as yours.

On the ''aligning the press tone response to a target using tone reproduction curves in the RIP'' , i always thought and called it calibration,but i could use any other word as long as it's better describes this procedure!

My ''argument'' towards the two curves policy,is that when you linearize the plates and then apply the tone reproduction curve to to them to meet house or other standard,if you change plate vendor you must only linearize the new plate,and the tone reproduction curve remains the same -as long as the press prints consistently.

On the other hand,when you apply only the tone reproduction curve which compensates for the non linearized but consistent plates as well,and you change plate vendor,then you must create a new tone reproduction curve,which i think is a more challenging and costly procedure -which could explain maybe why so many printers like you said go with the two curves option-

Being not a native english speaker , and keeping in mind what you say in your signature may leads to misunderstandings,but either way thanks for your time answering this -and so many others-

 

[motormount]

John,i wasn't talking about changing from positive to negatives or the opposite,but changing from trillian to some chinese manufactor for example.But if positive and negative plates print different then even a linearized positive could print different from another's vendor linearized positive-depending on the grain and likewise factors-


In that case a two curves policy is no good from any point of view...

 

[gordo]

@chevalier

Reading the thread,and gordo's links afterwards,i had the question if in my case the two curves policy was a better than one.

Really sorry for jumping in,i should open another thread and thank very much you for your answer.

@gordo

On the linearization thing,i was meaning the same,even not put down in words as clearly as yours.

On the ''aligning the press tone response to a target using tone reproduction curves in the RIP'' , i always thought and called it calibration,but i could use any other word as long as it's better describes this procedure!

My ''argument'' towards the two curves policy,is that when you linearize the plates and then apply the tone reproduction curve to to them to meet house or other standard,if you change plate vendor you must only linearize the new plate,and the tone reproduction curve remains the same -as long as the press prints consistently.

On the other hand,when you apply only the tone reproduction curve which compensates for the non linearized but consistent plates as well,and you change plate vendor,then you must create a new tone reproduction curve,which i think is a more challenging and costly procedure -which could explain maybe why so many printers like you said go with the two curves option-

Being not a native english speaker , and keeping in mind what you say in your signature may leads to misunderstandings,but either way thanks for your time answering this -and so many others-

I understand that you are not a native english speaker. I try to be as precise as I can with the words I use so that I don't cause a misunderstanding. Even native english speakers very often use words incorrectly in the print industry. That causes a lot of misunderstanding and muddled thinking. I've experienced that directly in the many shops that I've visited over the years. In fact, my policy when talking to management or production workers is always to have them define what they mean when they used certain terms. You'd be surprised that in many shops, production workers don't always use the same words to mean the same thing. One of the big ones is that press operators often use "Red" to mean "Magenta" and "Blue" to mean Cyan - which is not what the people in their press department mean by Red and Blue.

RE:

My ''argument'' towards the two curves policy,is that when you linearize the plates and then apply the tone reproduction curve to to them to meet house or other standard,if you change plate vendor you must only linearize the new plate,and the tone reproduction curve remains the same -as long as the press prints consistently.

I can only speak from my experience. Changing plate vendors is usually a big undertaking. There are usually tests done to "prove" that the plates will work in the shop before the change is made. There is plenty of opportunity to get the information needed to create a new tone reproduction curve. So, I don't think you would, for example, switch from a Kodak plate to an Agfa plate and expect to just apply a new linearization plate curve. Just because both plates are linear does not mean they will print the same.

The problem with using two curves (linearization curve then a press curve) is that you introduce an extra variable or point of failure. The other issue is that using two curves can lead to shade stepping (banding). I have seen that happen in my old shop (and others) when they complained about shade stepping with FM screening. When we removed the linearization curve they were using the shade stepping disappeared.

IMHO, most print shops use the linearization curve, and then a press curve because they are either still in a film world thinking mode where linear film is the standard or they are going by intuition or they just haven't really thought it through.

There certainly are some cases where it can be argued that a two curve policy is best. This is usually when there is one person who is responsible for several printshops at different locations running different CtPs and plates. It could make his job easier to diagnose a problem if it happens in one of the shops.
But for the vast majority of print shops running one or two CtP devices having a two curve workflow just complicates things and provides no benefits.

 

[motormount]

ok,thanks again!

 

[Greg G]

So, I don't think you would, for example, switch from a Kodak plate to an Agfa plate and expect to just apply a new linearization plate curve. Just because both plates are linear does not mean they will print the same.

Please could you expand on this Gordo. Would a new linearization not work because of a different brands response of the emulsion's chemical makeup to the laser?
Personally if switching brands, I would relinearize (if necessary) and build a new TVI curve.

 

[gordo]

So, I don't think you would, for example, switch from a Kodak plate to an Agfa plate and expect to just apply a new linearization plate curve. Just because both plates are linear does not mean they will print the same.

Please could you expand on this Gordo. Would a new linearization not work because of a different brands response of the emulsion's chemical makeup to the laser?
Personally if switching brands, I would relinearize (if necessary) and build a new TVI curve.

You can linearize the different brand/type of plate but I believe that the difference in plate graining, water pickup, and coating difference could be sufficient to result in a difference in tone reproduction in the presswork. I seem to remember this was a side discover from a press test done at GATF (who tended to run things linear). But I could be wrong.