Ctp plate curves for screens

gkwallace

Member
I understand making plate curves for 4 color process, i.e creating a plate curves to hit certain tvi for a standard like fogra, but what about single color screens like you would see in a business form?
A dot gain of 15 on a 50 is pretty extreme.
How should I build my curve?
Make a plate, hit color density on press and read the screens on the printed sheet?
Thank for the help.
 
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SteveSuffRIT

Well-known member
You said "A dot gain of 15 on a 50 is pretty extreme."?
Actually , it sounds just about right if it's on a gloss coated paper.
ISO 12647-2:2015 states a Tone Value Increase (TVI) of 16% for gloss coated paper. This uses conventional Murray-Davies (N=1) formula.
You mentioned a business form, so probably an Uncoated offset paper, so that is an ISO 22% TVI.
Also, if a spot color (Pantone), then use the Spot Color (SCTV) method to calculate tone value, which is ISO 20654:2017 which was created by Spot Color Halftone Method Optimization Organization (Schmoo).
Steve Suffoletto
 

SteveSuffRIT

Well-known member
Additional follow-up:
The TVI will be dependent on Solid Ink Density (SID), more ink, larger dot (mechanical/physical)
Also, screen ruling frequency or lpi, finer lpi, more TVI (optical)
 

gordo

Well-known member
Additional follow-up:
The TVI will be dependent on Solid Ink Density (SID), more ink, larger dot (mechanical/physical)
Also, screen ruling frequency or lpi, finer lpi, more TVI (optical)
Which is why dot gain, as the ISO target, was the wrong metric to have been chosen - unless your print conditions, as Steve listed, are exactly as specified by ISO. If the print conditions are different then dot gain is a meaningless target.
 

gkwallace

Member
Great wisdom guys.
On an uncalibrated plate my 50 was printing 72 on uncoated not very smooth stock.
I think I'll just work it down with a well distributed curve and call it a day. Pantone tints are a bitch and there's no way around that.
 

gordo

Well-known member
Great wisdom guys.
On an uncalibrated plate my 50 was printing 72 on uncoated not very smooth stock.
I think I'll just work it down with a well distributed curve and call it a day. Pantone tints are a bitch and there's no way around that.
Just a sidebar regarding screen tints of PMS inks. In my experience, they are formulated to print as solids and not halftone screened (nor over printed). You might try telling you ink supplier how you will be printing the ink - I.e. halftone screening it - and he might be able to adjust the formulation accordingly.

On the left a standard halftone screened PMS Orange and on the right the Orange ink adjusted to be screened.
two oranges.jpg
 
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gkwallace

Member
Just a sidebar regarding screen tints of PMS inks. In my experience, they are formulated to print as solids and not halftone screened (nor over printed). You might try telling you ink supplier how you will be printing the ink - I.e. halftone screening it - and he might be able to adjust the formulation accordingly.

On the left a standard halftone screened PMS Orange and on the right the Orange ink adjusted to be screened. View attachment 289914
I'm printing on an almost new SM52. New rollers, new blankets, new Techkon spectrodens. My Screen 4300S was just calibrated by agfa. The press runs and prints like a dream. If I get the plates right the only variable is me and my skill. That's my theory and I'm sticking to it 😆
 

gordo

Well-known member
I'm printing on an almost new SM52. New rollers, new blankets, new Techkon spectrodens. My Screen 4300S was just calibrated by agfa. The press runs and prints like a dream. If I get the plates right the only variable is me and my skill. That's my theory and I'm sticking to it 😆
None of that matters if the ink is no good.
 

Slammer

Well-known member
Which is why dot gain, as the ISO target, was the wrong metric to have been chosen - unless your print conditions, as Steve listed, are exactly as specified by ISO. If the print conditions are different then dot gain is a meaningless target.
Why? If your SID´s are in specification then you should be able to use the TVI´s as a target. Just two weeks ago I did a Rapida and gloss and matt stock using the suggested TVI values supplied by the K&B technician.
 

gordo

Well-known member
Why? If your SID´s are in specification then you should be able to use the TVI´s as a target. Just two weeks ago I did a Rapida and gloss and matt stock using the suggested TVI values supplied by the K&B technician.
SIDS are a specification because they are an indirect measure of ink film thickness. If SIDS are not within specifications then the lithographic process will fail.
TVI is a process control metric. You measure it through production to monitor dot distortion. If at any point in the process the distortion/dot gain varies from what is expected then you have a signal that there is a problem and where it has occurred.
Tone reproduction - I.e. a tone curve measured on the press sheet - is, IMHO, the appropriate target for a print specification. I.e. you should print to a specified tone reproduction curve irrespective of what dot gain you have. That way, the tone appeared is normalized across different screening and substrates. One ISO Curve instead of a whole bunch of different ones.
But, of course, that’s not what’s done.
 

gordo

Well-known member
TVI and Dotgain are one and the same unless I am totally wrong.
You are both right and wrong (hey, it's printing)

Dot gain (or loss) describes the distortion of the dot during the process. The consequence of the distortion is a change in the simulated tone value. Since printers are concerned with tones in their presswork they use instruments designed to report the tone values simulated by the halftone dots. Recently, the term "TVI" (Tone Value Increase) has been adopted to more accurately describe what's going on. Historically the term used to describe what's going on is/was "dot gain/loss". I.e. the cause rather than the effect.

The only people that I know that measure the actual physical size of halftone dot are engineer types - and they use specialized tools for the job and also typically measure the dot in microns (a linear dimension) rather than % (a tone value).

For all practical purposes and to maintain historical continuity as well as clarity the terms can be used interchangeably unless there's a specific reason to not do so.
 

gkwallace

Member
So I ended up printing a full sheet filled with screens from an uncalibrated plate, input the values read and voila, dead nuts first try.
Thanks for the help everyone.
 

gordo

Well-known member
So I ended up printing a full sheet filled with screens from an uncalibrated plate, input the values read and voila, dead nuts first try.
Thanks for the help everyone.
It was calibrated - it just didn’t have a curve applied.
Your experience has been the same as mine in many shops.
 
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