Calibrating New Equipment

[duck]

We finally bought a used platesetter and other various equipment to join the rest of the modern print world. The idiots who sold it to us have no clue what they are doing. We're in week #7 of install and set-up, but that's a whole other story.

Now that we know the guy who calibrated to the press didn't have a clue what he was doing, we've pretty much taken it upon ourselves to set up and calibrate everything.

Now here's the problem we're having internally. The owner is upset that everything is already printing light - part of it could be bad calibration, part of it is for the first time ever, we've compensated for dot gain (I had the film linearized, but there was absolutely no measure or control for gain on plate or gain on press). My thought is that we've been printing way too heavy and now have the opportunity to get it right. The other side of the argument is that we need to add some gain to the plates to print more consistent with the rest of the print industry.

How is everyone else calibrated?

Do you calibrate so that you print an actual 50% on the press sheet where it's spec'd as 50% in the file? Or do you allow for dot gain and print heavier? My understanding is that we should calibrate so the plates are linear (25% = 25%, 50% = 50% etc...) then build a curve for the press that compensates for the dot gain so that when the ink hits the paper, the 50% still = pretty darn close to 50% etc...

I guess it boils down to whether we should be printing the actual color and percentages or whether we should have some gain to match what we printed before and what other print shops print.

[Lammy]

you need to add gain to your plates.

easiest thing for you is going to be to make a set of analong plates with percent scales on them. Print the scales and read in the percentages you get off the press. Make a set of digital plates with no curves applied and run those. Then build a curve to adjust the results of the uncurved plates to match the gains you see on the analog plates.

I know it's over simplified and not the best way, but for your situation it may get you back to something normal sooner than later.

[UncleSam]

You print way way way too light! If your press print 50% at 50%, everything will looks light! Since according to the standard (SWOP or GRACol), the 50% should read 68%-70% on the press! That will give you most neutral looking image. You need to recalibrate your CTP!

[billzeeabob]

We have gone through the exact same thing as you.

A 50% K in the file should be about 68% dot area on the paper. Why? Because that is the way it always has been and everything is built around it.

You should linearize your CTP (i.e. 50%=50%), turn off any colour managment and run a calibration sheet at your standard densities. On the chart, you should have steps from 0 to 100% for each channel which correspond to the adjustment points in your RIP's curves. We target the following at 50%:

C: 63.0%
M: 64.5%
Y: 65.5%
K: 68.0%

We picked these numbers from some GRACoL literature on G7. They work pretty good. You could have CMY all the same if you wish but K should be highest.

If you get substantially higher than 70% at 50% on the step chart, your press likely needs a tune up. Too much blanket pressure, over packed blanket/impression, fountain conductivity out of whack, etc. When I started figuring this out, we were printing 88% at a 50% on K! We had to fix everything on our press.

Once you have your step chart results (and if necessary tuned up the press and rerun your calibration sheet) THEN adjust your RIP to get the target dot gain. You should only have to knock it back about 1-3% if your press is healthy.

I have learned alot coming out of the dark of the film room -- no thanks to equipment vendors. Feel free to send me an email and we can talk by phone.

Bill

[MarkTonk]

Everyone has brought up good info here. You are too light for sheetfed and way to light for web. Make sure the press in in good operating conditions before proceeding or you will be doing this again later when it is. No real old warn blankets, right packing, etc. Make sure your are properly exposing the plate. You do not have to linearize the plate if you are going to add a curve. what counts is the dot gain on paper. However, if the plate you are using in not too linear, you may want linearize it. Get a QC strip from the plate manufacture, it should provide a test scale with and with out curve. This way, without curve, you can check the 50 to be a 50% as a QC step. If you were content with previous printing, then Lammy is right, follow his test and make curves to match. If not, then for sheetfed, on a good coated stock, you will typically have 18 to 20% gain so a 50 will be 68 to 70%. Make sure when you run the test the pressman runs to standard house densities and the sheets are even across. You may want to read several sheets and average the dots. Once you have the right weight, you can tweak the curve for gray balance if need be.

What is your standard screen ruling? With CtP, you can step it up a bit and provide higher quality ....while your at it.

Out of curiosity, what CtP do you have and what plates are you using?

Regards,

Mark

[ICC_Color_Management]

Attention!, those numbers are not specially the one you need to get proper gray balance! It depend on you paper, inks, etc.
Make sure that if you do use those numbers, you get good gray balance at the same time.

Louis Dery
TGLC inc.
PerfX Press Curves™

Originally Posted by billzeeabob

We have gone through the exact same thing as you.

A 50% K in the file should be about 68% dot area on the paper. Why? Because that is the way it always has been and everything is built around it.

You should linearize your CTP (i.e. 50%=50%), turn off any colour managment and run a calibration sheet at your standard densities. On the chart, you should have steps from 0 to 100% for each channel which correspond to the adjustment points in your RIP's curves. We target the following at 50%:

C: 63.0%
M: 64.5%
Y: 65.5%
K: 68.0%

We picked these numbers from some GRACoL literature on G7. They work pretty good. You could have CMY all the same if you wish but K should be highest.


Bill

[duck]

MarkTonk: we are using a Screen 'Dart' platesetter with Fuji processless plates. The problem with processless is that you can't really see the image on the plate, and apparently can't use a reflective densitometer to read it.

The install company is back to square one as of today. We are going to film on jobs for today while they start from scratch on the platesetter. I think bossman is having them hire someone from Kodak who does calibrations to set us up, as no one who has been here so far has a clue what they are doing.

Anyway, thanks for all the replies. I guess we want the same amount of dot gain that we had with film and plates. Still seems a little crazy to me, but as long as someone sets this up who knows what they're doing, it's not my problem anymore!!!!

Interesting side note: going back to the broken e-bay brisque is actually a nice change from this xitron set up we've started using! Kinda makes me wonder why we went direct to plate at all. We got a slower more PITA rip, we're putting back in the same dot gain we had anyway - why not just stick with film?

[MarkTonk]

Originally Posted by duck

MarkTonk: we are using a Screen 'Dart' platesetter with Fuji processless plates. The problem with processless is that you can't really see the image on the plate, and apparently can't use a reflective densitometer to read it.

The install company is back to square one as of today. We are going to film on jobs for today while they start from scratch on the platesetter. I think bossman is having them hire someone from Kodak who does calibrations to set us up, as no one who has been here so far has a clue what they are doing.

Hi Duck,

One of the reasons Heidelberg decided on Chemfree plate technology over processless is the Chemfree has good contrast, you can visually see and measure the image. You can QC the plate before press.

Have you tried talking to your Fuji representative? It's their plate your buying and they will know how to set up their plate. Fuji's thermal CtP devices are manufactured by Screen, so they are familiar with them too.

There was some talk awhile ago about some plate readers that would be able to read the processless plates. I do not know if they are available yet but they did have a price premium to be able to read it. Fuji would also know if their are any plate readers to read the processless plates.

That being said, CtP is a great leap forward and you will love it once you have it set up properly. Good luck.

Regards,

Mark