Does anyone know the target dot gain value of a heatset web press?

[Bloodsaler]

I`m doing a web press test now.I want our press match the condition that swop requiered.I use some G7 method in the test too,but for the cost of a web testing,it`s not totally successuful~The NPDC curve indicate something that how i should adjust our dot in prinergy,but the confirmation run shows the result not match the target npdc curve.
So now i need some target dot gain value of the heatset web press,that i can use tvi method to adjust our press.But I read through the SWOP specification,only find the target value of 50% area,the other part like 25%and 75% area didn`t show how the dot increased,anybody knows the target value of these area?So I can check my tvi curve then adjust it~
Thanks

 

[maas]

The variables that determine dot gain are many, the bell shaped curve is a relatively good indication on dot gain in lower and higher percentile tonal area's.

however stock, ink, chemistry (alcohol) all play a major part, there is no magic curve that will cater for everything.

question- why go for SWOP?

regards
Maas

 

[Bloodsaler]

For we have sheetfeed and weboff press too,some of our production the client require the sheetfeed part achieve gracol,for the color consistency,so it`s better if our web press can acheive swop~

 

[gordo]

@ Bloodsaler

You might be misunderstanding things a bit - or maybe I've misunderstood you.

The reason that SWOP, historically, specified dot gain only at the 50% tone was because the halftone screening used was Euclidean (round/square/round) where 51%-100% is simply the negative of 0%-49% and since SWOP is an input specification (i.e. SWOP is for proofs - not press) providing a dot gain value for 50% is all that's needed since on a proof the 0%-49% would mirror the dot gain of 51%-100%. Graph it and you get a nice symmetrical curve. Of course a press is a bit different.

According to SWOP, "the printer's primary responsibility is to match the appearance of the supplied SWOP proof on press." You make a SWOP proof by using an IDEAlliance Certified Proofing System and follow the directions for that system contained within the Application Data Sheet. Once you've got a SWOP proof made according to the recipe you then do whatever you need to do on press in order to match it.

G7, on the other hand is a method (there are others) for attaining a desired greyscale and tonal curve for calibrating a proofing and/or printing system. I.e. G7 is for neutrals - not color.

hope this helps a bit. gordon p

 

[Bret Hesler]

This does not work for CMY, but, for K values, you can convert L* to density and then calculate dotgain from there. Assuming Swop 2006 Coated #3 values, dot gains as follows 25 - 16.4, 50 - 20.2, 75 - 14.4. Figure on CM and M being about 2% less at the midtone and Y 2% less than C and M. These calculations were done using the companding calculator and the dot gain calculator from brucelindbloom.com

Now, as far as G7 not working on a web press, I have seen sometimes when there is a large correction (around 12-15%) the calculation is not always the most accurate, and will require a second adjustment (and pressrun) based on the first curve. Also, I have had "helpful" press operators re set rollers and replace blankets while I was making curves and curved plates for verification, invalidating the initial linear pressrun conditions.

To clarify a bit, the Gracol and Swop datasets from 2006 are built on the G7 tone curve and gray balance. So, setting up your press with G7 curve and Gracol or Swop solid/overprint aims will get you a pretty good match proof to press, with caveats for super brightened paper and exotic screening.

Bret

 

[J]

This does not work for CMY, but, for K values, you can convert L* to density and then calculate dotgain from there. Assuming Swop 2006 Coated #3 values, dot gains as follows 25 - 16.4, 50 - 20.2, 75 - 14.4. Figure on CM and M being about 2% less at the midtone and Y 2% less than C and M. These calculations were done using the companding calculator and the dot gain calculator from brucelindbloom.com

My understanding is that doing it that way you won't get the same dot gains that you would if you were to measure the sheet with a densitometer.
In the G7 How to guide it says: "2.9 G7 TVI curves and calculations - CAUTION: TVI numbers and graphs shown in this document for CMY inks are NOT the same as produced by a traditional densitometer, regardless of filtration or polarization status."

Is that correct?

J

 

[Bret Hesler]

That is correct. CMY do not correlate well from XYZ dotgain to densitometer dot gain. Black however does. The figures for C and M being 2% less are from historical references and averages.

Bret

 

[Bloodsaler]

This is the tvi curve before calibration run,not finding some serious problem in it.But during production run,our operator often find some color especially the skintone,can`t match the proof~