tone value increase

ar17

Well-known member
i have a new press which we are commissioning. initial run using linear plates show we have dot loss measure with a very ideal density achieve for cmyk. do i need to increase the plate curve to match the standard dot gain based on fogra 39L or G7 target? your inputs will be greatly appreciated.

best
 

SteveSuffRIT

Well-known member
If you want to match previously printed jobs (legacy) and/or match an industry specification like Fogra or G7, then yes.
A positive CtP curve is called a "bump", negative a "cut-back".
Continue to monitor the TVI, that "sharp" printing may be temporary until the press is "broken" in?
ISO 12647 expects 16% TVI @ 50% with 175lpi AM screening.
Out of curiosity, what where your TVI & SID on gloss coated paper? Was your linear plate within +/- 1%?
Steve Suffoletto
 

gordo

Well-known member
SteveSuffRIT;n288912 ISO 12647 expects 16% TVI @ 50% with 175lpi AM screening.[/QUOTE said:
I believe that’s based on linear film where with a positive film workflow that 50% on film will be about 48% on plate and with a negative film workflow that 50% on film will be about 52% on plate. ISO turning a process control metric into a target :p
 

curiosity

Well-known member
is it just me?

how does one get "dot loss measure", which I might be incorrectly assuming means negative gain?
another assumption is you're printing on paper, with inks, etc. (sarc - sortof)
 

gordo

Well-known member
is it just me?

how does one get "dot loss measure", which I might be incorrectly assuming means negative gain?
another assumption is you're printing on paper, with inks, etc. (sarc - sortof)
However they are printed, halftone dots become distorted as they go through the print process. The distortion results in dot gain or dot loss - with its consequent change in tone value - during the process. Dot gain or dot loss is therefore used as a process control metric (expected tone vs actual). It is incorrectly and unproductively defined as a target by the ISO folks.
 

Ulrich

Well-known member
SteveSuffRIT;n288912 ISO 12647 expects 16% TVI @ 50% with 175lpi AM screening.[/QUOTE said:
I believe that’s based on linear film where with a positive film workflow that 50% on film will be about 48% on plate and with a negative film workflow that 50% on film will be about 52% on plate. ISO turning a process control metric into a target :p
16% increase is the "ideal" increase for the condition sheetfed offset coated with the "newer" profiles based on FOGRA 51 for CMYK (the former FOGRA 39 based profiles expect an increase of 14,3 for CMY and 17% for K)

Dot gain or dot loss is therefore used as a process control metric (expected tone vs actual). It is incorrectly and unproductively defined as a target by the ISO folks
i argue in a very strong way that i did not get right what Gordo wanted to say with that, but i am absolutely sure that the peace or war status between the prepress- and print-section in a company (and after that between seller and customer) depends more from getting "ideal" increases (very espacially when cmyk-separated "black and white"-photography is to print...) than from "ideal" ink density to reach the "ideal" Lab-values in the solids, (they are depending in all cases from the stock paper white point, which often is to different from the white point in a used profile. Based on this reason they had developed FOGRA39 up to FOGRA51 to respect more that in real live there are so much papers whith OBAs that FOGRA39 is hardly or not to serve with judged in a strong way...)

IMHO the value of the ideal ink density is those, which leads as near as possible to the "ideal" increase. (in any case the increase do not care about a white point of the different stock papers in a way the solids did, so you can work reliable with...) ;-)

And of course it is not only distortion that causes increase, more important is light catching, isn´t it?

Best

Ulrich
 
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Ulrich

Well-known member
...initial run using linear plates show we have dot loss measure with a very ideal density achieve for cmyk.
will you please specify dot less measure: The 50% patch leads to 47% (or what else below 50%) in print or did not reach the aim 64% with i.g. 59%?
 

curiosity

Well-known member
However they are printed, halftone dots become distorted as they go through the print process. The distortion results in dot gain or dot loss - with its consequent change in tone value - during the process. Dot gain or dot loss is therefore used as a process control metric (expected tone vs actual). It is incorrectly and unproductively defined as a target by the ISO folks.
Gordo,

So you're saying there is actually a thing called "tonal value decrease"?
Dang...guess I just didn't think that was possible.
 

gordo

Well-known member
Gordo,

So you're saying there is actually a thing called "tonal value decrease"?
Dang...guess I just didn't think that was possible.
In a positive film workflow, film to plate, yes. Plate to blanket and blanket to plate the dot gains (tone value increases) from what was on the plate.
 

gordo

Well-known member
i argue in a very strong way that i did not get right what Gordo wanted to say with that,
The ISO target should not be dot gain. It should be a tone value. Put another way, it doesn't matter what dot gain the system has nor what lpi is being used the result, for example, should be that a 50% tone request in the file should measure 66% on the substrate.


IMHO the value of the ideal ink density is those, which leads as near as possible to the "ideal" increase.
That makes no sense.

Ink density is an indirect measure of ink film thickness. Offset lithography requires that the ink film thickness needs to be around 1.2 to 1.8 microns thick. Any more, or less, and the process fails mechanically. Ink film thickness measured indirectly using density is the only thing the press operator can control. Dot gain should not be controlled using density (i.e. ink film thickness). That's like using a hammer to drive a screw into wood.

And of course it is not only distortion that causes increase, more important is light catching, isn´t it?
Many factors affect dot gain or loss. What matters is to understand when and how the dot changes are expected to occur so that, if the print result fails to meet expectations, one can diagnose the problem and apply any needed correction.
 

curiosity

Well-known member
In a positive film workflow, film to plate, yes. Plate to blanket and blanket to plate the dot gains (tone value increases) from what was on the plate.
Got it. My assumption was that the OP was referring to ink on paper..."Plate to blanket and blanket to plate".
 

alibryan

Well-known member
i have a new press which we are commissioning. initial run using linear plates show we have dot loss measure with a very ideal density achieve for cmyk. do i need to increase the plate curve to match the standard dot gain based on fogra 39L or G7 target? your inputs will be greatly appreciated.

best
As long as the press is printing so sharp, I would think that you only need to change your plate curve a little bit, really. A plate curve is usually applied in response to a printed dot gain (or loss), and is only used to compensate for it. So rather than an expected or pre-determined amount (sort of ridiculous), it should really only be whatever is needed to achieve the targeted tonal value.
 

SteveSuffRIT

Well-known member
Pressure:
Plate to Blanket = Squeeze. Is usually a constant.
Blanket to Paper = Impression. Adjusted for caliper thickness of paper.
Roller to Plate = Stripe. Press should drive form roller, not plate.
Steve Suffoletto
 
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Ulrich

Well-known member
IMHO the value of the ideal ink density is those, which leads as near as possible to the "ideal" increase.
That makes no sense.
Yepp, Gordo is right as every time with that, but he cut this line from the context i wrote that... (and i failed using not all words neccesary to translate my thougts on that into the english language...)

What i just want to say in the original context "Calibration" of the poster is this:

When you set up a printing condition (via Calibration in the RIP and by examinizing the density for the solids in print to reach the as aim documented Lab-values, which are more on focus today than the former focus to reach a nearby perfect "printing contrast"(?)... ), my opinion and (a little bit experienced....) conviction is, you should look more at the curves which else ever you are using and creating or judging to get as near as possible the result on paper which is documented by the FOGRA folks for a special condition as having the focus on Lab-values for the solids. Of cause they are important too, but often you never have a chance to reach them because the white point of the used paper in stock is too far from that one in the matching profile, but you can do your best to prevent your colleagues in the printing section from issues they will have to get a fine result every day by creating a fine calibration...

Best

Ulrich
 
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danremaley

Well-known member
i have a new press which we are commissioning. initial run using linear plates show we have dot loss measure with a very ideal density achieve for cmyk. do i need to increase the plate curve to match the standard dot gain based on fogra 39L or G7 target? your inputs will be greatly appreciated.

best
Here, try this and let me know how it works!
1-Print this tone scale with linear plates (attached). Use "Deer" poster for density reference Coated & Uncoated!
2-Measure dot area.
3-Enter "Wanted" values into rip (no one ever gives you them) (attached).
4-Print with new adjusted plates.
Oh, you can use the same values for uncoated - lower densities of course - same procedure (linear plates then curved).
Let me know how it works!
 

Attachments

gordo

Well-known member
Here, try this and let me know how it works!
1-Print this tone scale with linear plates (attached). Use "Deer" poster for density reference Coated & Uncoated!
With CtP plates there is zero need to linearize the plates first.
 

danremaley

Well-known member
TRUE but - 2 reasons - #1-I don't trust Creo or Kodak and I want to be sure I'm printing a 1-2-3% dot accurately!
#2- When the bean counter up front decided to change plates all I need to do is linearize - curve stays the same!
Oh, and by the way, on a previous post you thought on a negative film plate , a 50% became 52%.
No- I measured it- a negative 50 becomes 54% when the exposure is 6-8 microns (UGRA).
On a bulb that has the correct UV - bulbs were expensive, so they never changed them - those 50% became 60% Ha Ha
 

gordo

Well-known member
#1 Linearization is separate from a CtP plate/platesetter’s ability to image a 1,2,3% dot accurately. Besides the size of those dots are variable. When a CtP device is calibrated by the engineer it is set up to image 1, 2, 3, etc pixel features - not % - since halftone dots are built with clusters of single pixels.
#2 If you don’t linearize your plates but only use a tone reproduction curve then, if you change plates then all you need to do is adjust your tone reproduction curve so that it delivers the same dot curve on the new plate that was delivered on the old. I.e. you only have one curve to adjust - just like with your two curve set up.
 

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