Dot Gain before press

[richie44]

I was doing some process checks the other day and came across this anomaly . I made the 1-bit Tiffs through the RIP with linearisation and press curves applied and read the 50% patch which came out as 52%, I then made some plates from the Tiffs and read the same patch and it read 67% !?. Am I missing something, I have done linear checks on CTP and they are in tolerance, the CTP has recently been checked and maintained. The plates are UV processless.

Someone suggested that it was a allowance for dot sharpening on press.

 

[mwc]

in the first step - 50 = 52%, where are you getting this measurement? off the digital file, or is this off the plate?
in the second step, you mention the plate reads 67 in the 50...this seems about normal depending the the amount of gain you need on press...(if the first step is off the digital file, I'm assuming you are adding some gain to the plate when processed/output)

 

[richie44]

in the first step - 50 = 52%, where are you getting this measurement? off the digital file, or is this off the plate?
in the second step, you mention the plate reads 67 in the 50...this seems about normal depending the the amount of gain you need on press...(if the first step is off the digital file, I'm assuming you are adding some gain to the plate when processed/output)

In the first instance I am getting the measurement off the digital TIFF file.
In the second instance I am getting the measurement off the plate made from the above TIFF file.
What does not make sense is that any dot gain compensation has already been applied to the TIFF and then that is exposed to the plate without any further curves,
so how can the dot be greater once exposed on to the plate.

 

[gordo]

In the first instance I am getting the measurement off the digital TIFF file.
In the second instance I am getting the measurement off the plate made from the above TIFF file.
What does not make sense is that any dot gain compensation has already been applied to the TIFF and then that is exposed to the plate without any further curves,
so how can the dot be greater once exposed on to the plate.

This isn't making sense.
You appear to be screening the file and rendering it as a 1 bit tiff. Then sending that 1 bit tiff for exposure to the plate.
The 1 bit tiff should measure 50% at the 50% patch because it is a digital file where the halftone dots have not yet been mechanically distorted.
When that 1 bit tiff gets exposed to the plate then there will be some distortion caused by the mechanics of imaging.
In a properly set up CtP device that dot distortion will typically result in a 50% tone being rendered as 50% +/- 2%. i.e. it should measure between 48% and 52%.

For you to get 67% either how you're measuring the plates is faulty, or the screened 1 bit tiff is not the data that's being imaged to plate.

 

[richie44]

This isn't making sense.
You appear to be screening the file and rendering it as a 1 bit tiff. Then sending that 1 bit tiff for exposure to the plate.
The 1 bit tiff should measure 50% at the 50% patch because it is a digital file where the halftone dots have not yet been mechanically distorted.
When that 1 bit tiff gets exposed to the plate then there will be some distortion caused by the mechanics of imaging.
In a properly set up CtP device that dot distortion will typically result in a 50% tone being rendered as 50% +/- 2%. i.e. it should measure between 48% and 52%.

For you to get 67% either how you're measuring the plates is faulty, or the screened 1 bit tiff is not the data that's being imaged to plate.

Thanks for your response Gordo.

Just to clarify, the plate technician came in to investigate and he advises me that when doing a new install without any curves in place, he would expect at 50% to get 58% reading which would be ideal. This is due to the mechanics of UV exposure. We have then applied a linear curve based on these readings to bring the CTP to a linear state. Then we apply a dot gain compensation curve as a result of the fingerprinting tests and the curve requests a 61% at 50% to hit the IFRA standard of 76% at 50% on the press sheet.

What does not make sense is that we read the TIFF at 50% and the file says 50%, how does that same TIFF make 67% at 50%.
I have done the same readings from other technicians dot readers just to eliminate my device being at fault.
The plate manufacturer has been in and check everything and found no faults with laser power, plate chemistry, pre-heating, PH of dev etc.

Although I am confident that the curves in place are accurate and we are printing ok, I just want to try and explain how a TIFF reads 50% and the plate reads 67%.

 

[gordo]

Thanks for your response Gordo.

Just to clarify, the plate technician came in to investigate and he advises me that when doing a new install without any curves in place, he would expect at 50% to get 58% reading which would be ideal. This is due to the mechanics of UV exposure. We have then applied a linear curve based on these readings to bring the CTP to a linear state. Then we apply a dot gain compensation curve as a result of the fingerprinting tests and the curve requests a 61% at 50% to hit the IFRA standard of 76% at 50% on the press sheet.

What does not make sense is that we read the TIFF at 50% and the file says 50%, how does that same TIFF make 67% at 50%.
I have done the same readings from other technicians dot readers just to eliminate my device being at fault.
The plate manufacturer has been in and check everything and found no faults with laser power, plate chemistry, pre-heating, PH of dev etc.

Although I am confident that the curves in place are accurate and we are printing ok, I just want to try and explain how a TIFF reads 50% and the plate reads 67%.

I am not a fan of using two curves (press curve on top of a linearizing curve). It usually adds complication and point of potential failure, for most shops, without providing any benefit. It also makes diagnosing where the problem is more complicated.

I am an old man, so for clarity you need to be explicit in following the tone trail.

Forget dot gain - just think in terms of requested tones, expected tones, and delivered tones.

So, is this correct:

50% requested in file = between 50% to 58% on plate.

The you say: "We have then applied a linear curve based on these readings" What readings? How can you build a linearization curve based on a platesetter delivering anything from 50% to 58% from a requested 50% tone? If that is correct then I would return the platesetter.

So, you made a linearization curve to remap the file tone request to X% (you didn't say).
Then you apply a tone curve to that linearization curve to remap the X% to deliver a 61% on the plate?
Does that 61% on plate have the same potential tone deviation as a 50% does (i.e. a range of 8%)?

That being said, a 61% tone on the plate delivers the required 76% tone on press for a 50% tone in the file. Correct?

Then you say: "the TIFF at 50% and the file says 50%, how does that same TIFF make 67% at 50%."

Where is the 67%? On the plate? On the press?

 

[richie44]

Thanks for your response Gordo, Please see my responses below.

50% requested in file = between 50% to 58% on plate. No, it does not vary from 50 to 58, it is consistently 58%

The you say: "We have then applied a linear curve based on these readings" What readings? How can you build a linearization curve based on a platesetter delivering anything from 50% to 58% from a requested 50% tone? If that is correct then I would return the platesetter. The platesetter consistently delivers 58% in the 50% patch, for simplicity, I am not going provide the readings for 10,20,30 etc I will just refer to the 50% reading.

So, you made a linearization curve to remap the file tone request to X% (you didn't say). 50% to 50%
Then you apply a tone curve to that linearization curve to remap the X% to deliver a 61% on the plate? 50% to 61% on plate.
Does that 61% on plate have the same potential tone deviation as a 50% does (i.e. a range of 8%)? No because the Linear curve eliminates it.

That being said, a 61% tone on the plate delivers the required 76% tone on press for a 50% tone in the file. Correct? Correct

Then you say: "the TIFF at 50% and the file says 50%, how does that same TIFF make 67% at 50%." This is exactly what I am trying to establish.

Where is the 67%? On the plate? On the press? On the plate.

 

[oxburger]

Based on your info, from what I gather you are:

1. Consistently getting a 58% when you read the plates imaged with a 50% 1-bit image.

The platesetter consistently delivers 58% in the 50% patch

2. Setting up a curve to bump the 50% to 61% (which is supposed to give you 76% at press.)

3. When you image the plate with a 1-bit image reading 61% (based on your curves), it is coming out at 67%.

Is that correct?

Or is it the 50% 1-bit imaging at 67% as mentioned in your original post?

Sorry, late to the party.

Could it be a batch of bad plates? or did the plate guy check those as well?

 

[gordo]

[SNIP]

Could it be a batch of bad plates? or did the plate guy check those as well?

Could be the batch of plates. It could also be that plates are not fully vacuumed to the plate holder. I.e. parts of the plate are slightly raised which would change the imaging spot size and hence the dot sizes in that area. Have you tried imaging the entire plate with just the linearization curve so the plate is entirely covered with a 50% tone? Then measure upper left/bottom left/upper right/bottom right/top center/bottom center/left center/right center/plate center to see if the plate measures 50% across it's surface.

 

[kansasquaker]

I am not a fan of using two curves (press curve on top of a linearizing curve). It usually adds complication and point of potential failure, for most shops, without providing any benefit. It also makes diagnosing where the problem is more complicated.

I second that. I have a new plate vendor doing an install right now and they're insistent that I linearize plates. I told them before I ever agreed to this that I don't linearize plates and don't want to. Here's the conversation:

Me: What are the benefits of linearization?
Them: If your plates fall out of spec, you can fix it.

Me: Well I don't see a linearized plate as a benefit, I only care about ink on paper. Moreover, I don't have any way to reliably read a dot on the plate other than my Techkon SpectroDens which isn't really a plate reader.
Them: Well we can read it for you and do the linearization.

Me: How will I know if the plates fall out of spec then?
Them: Well you can buy a device to read plates.

Me: Why would I want to do that?
Them: So you can save money if the linearization fails. Then you won't have to go back on press and build new curves.

Me: ?!*#!@&^%#@!!@*%^@!#

 

[gordo]

I second that. I have a new plate vendor doing an install right now and they're insistent that I linearize plates. I told them before I ever agreed to this that I don't linearize plates and don't want to. [SNIP]

I don't want to take this thread off topic - but just to answer your post, here are a few scenarios with a one curve workflow vs a two curve workflow:

One CtP & one plate shop - to achieve the same final result on press:
One curve workflow: one press curve = one curve total.
Two curve workflow: one linearization plate curve plus one press curve = two curves total.

One CtP & one plate shop using three different curves to optimize for three different papers. To achieve the same final result on press:
One curve workflow: one press curve per paper type = three curves total.
Two curve workflow: one linearization plate curve plus one press curve per paper type = four curves total.

One CtP & two plate shop - to achieve the same final result on press:
One curve workflow: one press curve per plate type = two curves total.
Two curve workflow: two linearization plate curves plus one press curve = three curves total.

One CtP & two press shop - to achieve the same final result on two presses:
One curve workflow: one press curve per press = two curves total.
Two curve workflow: one linearization plate curve plus two press curves = three curves total.

One CtP & one plate shop - what happens if a new batch of plates do not perform as the previous batch did:
One curve workflow: modify one press curve so that the plate tones are the same as the previous plate batch = one modified curve total.
Two curve workflow: modify one linearization plate curve plus apply the standard press curve so that the final plate tones are the same as the previous plate batch = two curves total.

One CtP & one plate shop - what happens if the press curve needs to be tweaked/adjusted:
One curve workflow: modify one press curve to achieve the required tone reproduction on press = one modified curve total.
Two curve workflow: one linearization plate curve plus modify one press curve to achieve the required tone reproduction on press = two curves total.

One CtP & one plate shop - what happens if the CtP device is replaced:
One curve workflow: measure the new plate output and modify one press curve to achieve the same tone reproduction/dots on plate as with previous CtP = one modified curve total.
Two curve workflow: measure the new plate output and modify the linearization plate curve to linearize the plate then apply the existing press curve = one modified curve for two curves total.

 

[aqazi81]

I don't want to take this thread off topic - but just to answer your post, here are a few scenarios with a one curve workflow vs a two curve workflow:

One CtP & one plate shop - to achieve the same final result on press:
One curve workflow: one press curve = one curve total.
Two curve workflow: one linearization plate curve plus one press curve = two curves total.

One CtP & one plate shop using three different curves to optimize for three different papers. To achieve the same final result on press:
One curve workflow: one press curve per paper type = three curves total.
Two curve workflow: one linearization plate curve plus one press curve per paper type = four curves total.

One CtP & two plate shop - to achieve the same final result on press:
One curve workflow: one press curve per plate type = two curves total.
Two curve workflow: two linearization plate curves plus one press curve = three curves total.

One CtP & two press shop - to achieve the same final result on two presses:
One curve workflow: one press curve per press = two curves total.
Two curve workflow: one linearization plate curve plus two press curves = three curves total.

One CtP & one plate shop - what happens if a new batch of plates do not perform as the previous batch did:
One curve workflow: modify one press curve so that the plate tones are the same as the previous plate batch = one modified curve total.
Two curve workflow: modify one linearization plate curve plus apply the standard press curve so that the final plate tones are the same as the previous plate batch = two curves total.

One CtP & one plate shop - what happens if the press curve needs to be tweaked/adjusted:
One curve workflow: modify one press curve to achieve the required tone reproduction on press = one modified curve total.
Two curve workflow: one linearization plate curve plus modify one press curve to achieve the required tone reproduction on press = two curves total.

One CtP & one plate shop - what happens if the CtP device is replaced:
One curve workflow: measure the new plate output and modify one press curve to achieve the same tone reproduction/dots on plate as with previous CtP = one modified curve total.
Two curve workflow: measure the new plate output and modify the linearization plate curve to linearize the plate then apply the existing press curve = one modified curve for two curves total.

My head is spinning...