Linearizing out plates and recalibrating?

[Phish]

Hi all,

i am new to this place so firstly, hello to you all, i am Phil and work in a place called SEM Envelopes Ltd in Derby England. It is a small to medium sized print shop employing around 50 people.

The problem?

Keeping the colours to an iso standard.

We had recently switched to ISO 12647 and had everyone (more than once) re-calibrated or set up to print to this standard. We have had the Kodak Lotem done what seems like twice a month for the past 3 months, trying to keep its colour etc.

The main problem is that with all these altercations to our output device, i have no idea what's been done as well as neither understanding the manual as to how to re-calibrate it myself. Alot of the people that have come in have re-calibrated the machine without anyone watching, so no idea if what i am doing is right?

Can anyone try and put it into plain english as to how to go about this process? What and where to look etc?

We are using prinergy 5 which inturn is using Harmony 1.2.1.1.

Can recalibrate film no problem, is this simular? I am not used to 3 curves (Current/Target/Calibration)

Many thanks for your time, if any other information is needed then please ask.

Phillip.

[seejay]

Hi Phil,

In my experience, it is very unusual for a CTP device to 'wander'. Generally if/when the plate has been linearised then it tends to remain stable provided your processor/chemistry etc. is good.

As such, my first recommendation would by to measure and check your plate to see if it is wandering - we tend to do this twice a day by measuring a calibration patch on the plate (20,40,50,60,80). Measuring and logging this will determine whether your plates are imaging and processing consistently. Once you have established whether this is the case then you can start looking at your press processes.

[gordo]

There are two "calibrations"

1- the initial set up of the laser intensity on the CtP device. This is done to achieve a robust dot on the plate. The resulting plate may, or may not be linear (likely not).

2- The application of a tone reproduction curve to the plate to achieve the required tone reproduction in the presswork. This may or may not be a curve to linearize the plate. Unlike a film workflow, there is no need to linearize the plate. There is only a need to have the appropriate tones on the plate that provide the desired tone reproduction in your presswork.

In Harmony "Current" typically means the tone reproduction you get on press with plates calibrated as per #1 above. "Target" means the tone reproduction that you want to achieve on press (could be previous presswork or published ISO curves). "Calibration" is the curve that Harmony creates from the "Current" press response and the desired "Target" press response that will be applied to plates.
Harmony is typically used once to build your curves. For a complete explanation of how Harmony works go here: http://qualityinprint.blogspot.com/2...pensation.html


Once calibrations #1 and #2 are done, then as Seejay said, things should remain pretty stable. You monitor the plates to confirm that stability, and based on that you'll likely need to look at other places, like your possibly proofing and especially presswork for inconsistent performance. You should not be using plate curves or laser adjustments to correct for an unstable pressroom.


best, gordon p

[danremaley]

Hi all,

i am new to this place so firstly, hello to you all, i am Phil and work in a place called SEM Envelopes Ltd in Derby England. It is a small to medium sized print shop employing around 50 people.

The problem?

Keeping the colours to an iso standard.

We had recently switched to ISO 12647 and had everyone (more than once) re-calibrated or set up to print to this standard. We have had the Kodak Lotem done what seems like twice a month for the past 3 months, trying to keep its colour etc.

The main problem is that with all these altercations to our output device, i have no idea what's been done as well as neither understanding the manual as to how to re-calibrate it myself. Alot of the people that have come in have re-calibrated the machine without anyone watching, so no idea if what i am doing is right?

Can anyone try and put it into plain english as to how to go about this process? What and where to look etc?

We are using prinergy 5 which inturn is using Harmony 1.2.1.1.

Can recalibrate film no problem, is this simular? I am not used to 3 curves (Current/Target/Calibration)

Many thanks for your time, if any other information is needed then please ask.

Phillip.

Are you changing the plates because of changes to dot gain values on press?
danremaley@comcast.net

[Phish]

Firstly, many thanks for the replies.

Will go in order of replies if thats ok?

1) Seejay.

Thanks for the idea of checking the tint value readings from the colour bars that we use. I am in the process of finding a decent plate reader to take these readings, any good idea's?

I would have thought that with general maintenance and 2 yearly services, the lasers that create the dots should remain stable and not wonder too much even if we have been using this machine for around 4 years and when it was purchased by us, it was reconditioned. It was sold by Kodak which again should give you confidence that it has been checked etc so not convinced that our Lotem 800 is the problem.

As for what you said about the processor and chemistry, we are using an AGFA Asura plate that has been set up to be used on our Lotem. Onced exposed, the plate is then fed to a processor which simply washes out the non exposed area/emulsion and aplies gum, no chemicals are used except gum. This should not effect the plate in any way that i know of, one thing that has crossed my mind is that by using recycled gum, would the strength deteriate before the actual time allocated. Suppose that testing a plate daily with a plate reader will provide this information.

2) Gordo.

I have noticed you popping up all over the place recently, well all the places i have looked at concerning this issue anyways. I recently joined Bloggers as i wanted to read your blogs on there as i am finding these useful, will confess that i am lost a little of the time but i am trying to learn again after so long. Alot of information to take in aswell but where there is a will there is a way.

"1- the initial set up of the laser intensity on the CtP device. This is done to achieve a robust dot on the plate. The resulting plate may, or may not be linear (likely not)".

This was done when we had the plates changed recently, this is the usual requirement, i presume, of changing plates? As for it being linear, i will come to this later.

"2- The application of a tone reproduction curve to the plate to achieve the required tone reproduction in the presswork. This may or may not be a curve to linearize the plate. Unlike a film workflow, there is no need to linearize the plate. There is only a need to have the appropriate tones on the plate that provide the desired tone reproduction in your presswork."

This is something that i am interested in, i am trying to totally understand this and will read the link that you posted with your reply soon. We recently had a independant technician come in and give us the answers to the questions we have been trying to figure/find out.

What was confussing for us was that non of us knew totally how harmony worked, we seem to have loads of different curves but no idea of what they actually did or used for. I have tried reading the manual but whether due to my inability to understand it in a way to satisfy the needs of the required circumstances at hand or just it did not make sense, lol. I would class myself as handy with a computer and find these problems interesting so i asked for someone to come in and explain what was actually happening and how to understand the software that runs the colour/tonal reproduction on the plates. I now feel more reassured within myself of the understandings and how to use the software but what i was told and what you have mentioned a couple of times on various websites is the used of only one curve and not the 2 that i was shown.

The senario went-

Over the last month or so we have been having a problem with vignettes in which we was getting a banding effect or a sudden stop in the gradual tonal reproduction. We have tried to combat this by adjusting the curves in harmony but to no great effect. We have got by but i like things to be right so there can be no come back at all, if a job is worth doing etc. Due to also recently introducing ISO 12647 into the work place, we are not getting a match to our calibrated proofing system and our press. Everything, especially the yellow and magenta are out on mid to low tonal areas, like snow etc from press to proof. The proof looks great but the press is just not right. after seeing the readings from proofmaster i can see why. So with the information provided by proof master we are trying to correct the curves.

When the technician came in we outputted a plate on what we thought was the correct PLATE curve and also PRINT curve, the readings was not great. We then outputted a plate on just the PLATE curve, i was then informed that this should be a linear plate and all the tint readings should match or close enough, to a maximum of 2%. Again, these were not great so he said to output a plate using not PLATE curve or PRINT curve as then he could take readings and create a plate curve to linearize our plate. During these outputs we noticed the banding effects in gradients/vignettes. Once the readings were taken we then created the PLATE curve by putting the reading we had just taken into the CURRENT curve and then put a linear setting into a TARGET curve eg 10 20 30 40 etc. We then created the Calibration curve by linking these 2 curves. We now had our linear PLATE curve which was put in as default into Prinergy. We then outputted some plates and took a reading from these printed sheets and created a new PAPER curve on harmony. The readings from the printed sheets was the CURENT CURVE and the ISO 12647 standard as the TARGET curve which inturn created our new PRINT curve. Once again, we then set this as default into Prinergy as its PRINT curve.

Wow, been a long day and that took some work, lol.

What has confused me is that with reading, or is it the way i am understanding it, some of your posts online over the last couple of days, you have said you should only have to use one curve and not two. Did what we did mean we used two curves? A PLATE curve to actually linearize the plate and then a PAPER curve to create the PRINT curve? The way i am understanding your posts are just output a plate with large tonal areas that can be easily read straight from having the laser power set to a surficiant power setting to create the required dot on the plate. Take these readings and print straight to paper and then create your PAPER curve which in turn would create your PRINT curve to be used in Prinergy. There would be no use in a PLATE curve as you have just outputted using the basic default settings after setting the laser power, is that right?

3) Danremaley

"Are you changing the plates because of changes to dot gain values on press?"

Hopefully what i have put above gives you the idea of what you need?

We are due to have a service on the press as well which hopefully will sort out a few issues aswell.


Once again, many thanks for your time and hopefully hear from you soon.

Phil.

[danremaley]

Hi all,

i am new to this place so firstly, hello to you all, i am Phil and work in a place called SEM Envelopes Ltd in Derby England. It is a small to medium sized print shop employing around 50 people.

The problem?

Keeping the colours to an iso standard.

We had recently switched to ISO 12647 and had everyone (more than once) re-calibrated or set up to print to this standard. We have had the Kodak Lotem done what seems like twice a month for the past 3 months, trying to keep its colour etc.

The main problem is that with all these altercations to our output device, i have no idea what's been done as well as neither understanding the manual as to how to re-calibrate it myself. Alot of the people that have come in have re-calibrated the machine without anyone watching, so no idea if what i am doing is right?

Can anyone try and put it into plain english as to how to go about this process? What and where to look etc?

We are using prinergy 5 which inturn is using Harmony 1.2.1.1.

Can recalibrate film no problem, is this simular? I am not used to 3 curves (Current/Target/Calibration)

Many thanks for your time, if any other information is needed then please ask.

Phillip.

I personally like to make the plate linear, because, I like to look at vignettes and 1-2-3% dots to be sure they measure correctly. Sometimes (like with positive plates), the set-up guy, over exposes the background, to keep it clean, reducing the 50% file dot to 44-45% on the plate and the highlight dots 1-2-3% are blown out! Also if I print a linear plate, I know from experience, a new press will print with around 14-16% midtone gain (with a good pigment ink), so I have a base line. Here's my 3rd. and most important reason, if I ever change plate manufacturer I only need to linearize the new plate and all my previous curves Work!
Dan Remaley 412.889.7643

[gordo]

What has confused me is that with reading, or is it the way i am understanding it, some of your posts online over the last couple of days, you have said you should only have to use one curve and not two. Did what we did mean we used two curves? A PLATE curve to actually linearize the plate and then a PAPER curve to create the PRINT curve? The way i am understanding your posts are just output a plate with large tonal areas that can be easily read straight from having the laser power set to a surficiant power setting to create the required dot on the plate. Take these readings and print straight to paper and then create your PAPER curve which in turn would create your PRINT curve to be used in Prinergy. There would be no use in a PLATE curve as you have just outputted using the basic default settings after setting the laser power, is that right?

Unless you have have a unique, very special requirement, you should only use one curve - what I call a press (or print) curve. The purpose of that curve is to create the tone reproduction you require in your presswork.

The job of your CtP is to image plates consistently. It doesn't matter if a 50% request results in, for example, a 45% or a 57% on the plate. What matters is that every time you request 50% that it delivers the same tone. If your CtP imaging is not consistent then you cannot use any kind of curves.

In a CtP workflow, if your plate imaging is not inherently linear then you have two choices.

Choice 1 - First create a curve to make the plate linear ( a plate curve). Then create a second curve to be applied on top of the linearizing curve to create the dots on plate that you need in order to achieve the tones on press that you need (a press curve).

or

Choice 2 - Since the plate imaging is consistent (though not linear) simply create one curve to create the dots on plate that you need in order to achieve the tones on press that you need (a press curve).

With Choice 1, linearizing the plate is redundant since it will be overridden by the second curve. It does not provide any benefits. But it does make the workflow more complicated and hence make more opportunities for mistakes. It can also cause shadestepping (banding) in vignettes.

The laser power setting is to create a robust dot on the plate - not to linearize the plate, nor to achieve specific tones.

It helps to ask yourself exactly what is accomplished by linearizing the plate before applying a press curve.
Is it to bring the plate imaging to a specific status? Well, that should be the case without a linearizing curve. And if the CtP is so unstable that it does not have a consistent status then it is not possible to build linearizing curves.

RE: "I have noticed you popping up all over the place recently, well all the places i have looked at concerning this issue anyways. I recently joined Bloggers as i wanted to read your blogs on there as i am finding these useful, will confess that i am lost a little of the time but i am trying to learn again after so long."

Yes, I'm quite noisy. :-)

I started my blog because I was so frustrated at the lack of clear and accurate information about many of the basic issues in our industry. It caused me a lot of pain, and I've seen it cause pain with many printers.

Do not believe what I've written just because I wrote it. Look at my reasoning, and my arguments, then look at the arguments against what I say and make up your mind as to what is the right path accordingly.

best, gordon p

[gordo]

I personally like to make the plate linear, because, I like to look at vignettes and 1-2-3% dots to be sure they measure correctly. Sometimes (like with positive plates), the set-up guy, over exposes the background, to keep it clean, reducing the 50% file dot to 44-45% on the plate and the highlight dots 1-2-3% are blown out! Also if I print a linear plate, I know from experience, a new press will print with around 14-16% midtone gain (with a good pigment ink), so I have a base line. Here's my 3rd. and most important reason, if I ever change plate manufacturer I only need to linearize the new plate and all my previous curves Work!

OK I'll take #2 and #3

If you print with a linear plate and you're using an FM screen you're not going to get a 14-16% midtone gain since midtone gain is dependent on several factors including the screening.

The thing is that it does not matter what your mid tone gain is (in fact mid tone gain hasn't been published as a spec in North America since 2006). Dot gain is not a base line. The important thing is that the press exhibit good ink transfer, minimal deformation on the halftone dot, etc., etc.

If you change plate manufacturers, yes, you will need to create a new linearizing curve then you can simply apply your previous curves.

If I change plate manufacturers I will need to create a new curves to achieve the same plate dots that I had before. If I had 4 curves (pretty typical) then that means four new curves for me (three more than you). About 20 minutes more work for me. Agreed. But in the end, I will have a simpler workflow - total of four curves for me compared with your total of five curves - with less chance of errors and shadestepping issues caused by curving curves for me.

best, gordon p

[seejay]

Hi Phish,

we use the x-rite ic plate 2 to measure our plates - we've found that its a very good, easy to use peice of kit.

With regard to the Asura plate, we have been testing this for the last month and a half. Our tests have proven very successful, with the plate showing no signs of instability - our plan now, is to switch our production 100% over to Asura in the new year (we currently use Agfa Elite plates).

[Phish]

Hi all,

Many thanks for the replies once again, some great response which i have read and appreciate very much. I want to try and do this calibration thing myself and i am interested in trying out both ways of doing it, eg. Using only 1 curve and also using the 2 curve process.

We are looking into buying an X-Rite plate dot meter so we can read the plates properly and hopefully, away we go. One idea that has been brought up is putting a tint gauge somewhere on the plate in a non print area so we can check the plates every time they come out the processor and CTP. Failing that, we can just take a reading from the colour bars we use.

One thing today that has got our brains going is how well is the gum washing/developing the plates, is it too robust or do we need to change its speed etc. I am going to look into this and hopefully find out some answers, wether it be it off the internet or from the customer support team at AGFA, does not matter really as long as i know it is optimized for our plates. We are using an AGFA Azura C125 plate processor and with that Azura TS Gum, this equipment has been set up for us so i am desperate to find out anything i can about this processor that is not in the manual, such as the optimum speed and temperature of the unit to produce consistent results.

Other than that i can not think of anything else that can be effecting the plates in anyway to make them so inconsistent. I have a feeling that we are a studio that is constantly chasing our press and it should be the other way round or atleast a bit of both and not all one way. Maybe the case in a lot of work places but when something is wrong with a colour or job the first place the fellow workers go into to find out whats happened is Repro. Can we fix this and that and hence why so many curves i dear say have been made over the last 6 months or so.

Well, i am off here for the time being, once again, many thanks, all of your help, no matter how big or small, has proven to be a great influence in a good way, thankyou. I will keep a look out on these forums just incase i maybe able to help anyone like you have me.

Phil.