Dot gain standards

[bhm8hwcm]

Does anybody have some info on some standards that one can follow for TVI (dot gain) at different percentages. I come across info for TVI at 50% but I am interested in guidelines for highlights etc. I am runing a DI press and basically get the press to a linear state..ie. 50% dot prints 50% on press. So at my rip I add a dot gain curve so I get the results I want.

At the rip is a stock SWOP curve which produces following results:
5% 20%
Dot gain generates:
K - 14% 36%
M - 11% 35%
C - 13% 33%
Y - 11% 32%

Some technicians a while back put in some new curves with the following:
5% 20%
Dot gain generates:
K - 8% 31%
M - 8% 31%
C - 8% 31%
Y - 7% 28%

I find many screen tints with low percentages seem to print too light so I wanted to increase things but did not know if I should go back to the SWOP standards. I am also trying to run higher densitites so do not know if the SWOP standards would apply. I can fool around and try different values but I wanted to see if any info is out there on this.

Eventually I plan to test out Gracol and strive for Grey balance but this may be a little while yet.

 

[rich apollo]

Why wait? Go ahead and do the G7 calibration now. Not that tough and you're gonna' come out MILES ahead.

 

[jlind]

Rich: Maybe they should walk before they run. It makes me a little nervous that the 50% in the file is printing 50% on the sheet. Now that sure isn't SNAP GRACOL and SWOP. Printing must look really flat.
I suggest that the printer read a draft of ISO12647.
John Lind
Cranberry Township, PA
724-776-4718

 

[bhm8hwcm]

Hi John, no I am not printing linear. I basically print a test sheet with no calibration at the rip. Tints are read in and a calibration curve is added at the rip technically making the press now print linear. I then add a dot gain curve onto this so that I am printing with gain like a normal press. End result is the same as a conventional press...film, plate or CTP. I can basically control what kind of gain I get at the press simplly by adjusting curves.

What I am looking for is dot gain standards. Old way with film, plates, etc I believe generated gain of approximately 20-22% at 50%. With CTP nowadays my understanding is people are printing cleaner with images less full looking (some searches have yielded results of as little as 14% gain at 50). So my question is what kind of dot gain should I be aiming for at say 5, 10,25,50, 75 etc.

Some techs adjusted some curves awhile back for me, but when printing tints around 5-15% I would say the gain is too little ( lower than stop SWOP curves in the rip) and not correct which also affects the grey balance, etc. Rather than try all kinds of scenarios I was just trying to find some guidance as to where to what other people view as generating good results and pleasing colour. I am curious as to what peoples gain is for a 5% patch.

 

[meddington]

Hi John, no I am not printing linear. I basically print a test sheet with no calibration at the rip. Tints are read in and a calibration curve is added at the rip technically making the press now print linear. I then add a dot gain curve onto this so that I am printing with gain like a normal press.

I'm not sure I see the benefit of forcing linearity, then adjusting gains on top of that versus simply adjusting gains off the press's uncalibrated response.

ISO 12647-2 defines the entire curve. Approx. 3% gain at 5%, 7-8% gain at 25%, ect, for "postive acting" plates and paper types 1&2 @ 150 lpi.

I'm with Rich though. G7 defines tonality much less ambiguously.

 

[jlind]

bhm8:
There's your answer. Look it up in IS012647. I think on a DI plate, it will depend on what the minimum dot is that you can image, how close it is to the actual size you ask for in the file. Pretty hard to read that plate when it's on the press or off the press, very little contrast and read out. Do you print a plate scale and read what is ink on paper? That was the original Fogra method, print and measure, don't waste much time measuring the plate. Always tricky to begin with. Now, as for the G7 values, I'm under the impression, maybe the wrong impression, that these curves will vary with the press, the paper, the blanket, the ink, etc. Maybe we could get a comparison of Mike and Rich's full tone curves for a coated paper, compare them to the ISO numbers and see what differences we are talking about.
John Lind
Cranberry Township, PA
724-776-4718

 

[bhm8hwcm]

Hi thanks for all the feedback so far.

Yes I think I will buy the Standard...I thought this info might be freely available but it looks like it costs about $100...but that's not too bad when you consider press downtime, makeready etc.

I do not read the plate. I print raw grayscale patches to the press and read those in and then build curves to get the results I want.

I am seriously considering setting up for G7. I may look a trying to do it myself or hire someone. I was quoted $1000 by one guy to set up the press, epson proofer, xerox digital and monitors. Cost actually comes in less than I would have expected.

 

[jlind]

bhm8: That's real cheap. Get it in writing. Quick.
John Lind
Cranberry Township, PA
724-776-4718