Matching Color

[5624GM]

Hello, we are running G7 and we are having trouble matching proofs. Nothing has changed with the proofs(Epson 9900),Ink,Dot gain. Can different papers change color that much? And if so what do you guys do? Make paper profiles?We have to move densities on press, like moving the mag down 30 points. We are double checking everything.

 

[RickWhiteman]

I'd go back to whoever helped you set up the G7 qualifications and explain your issues. We had been having serious trouble matching dark blue/reflex blue range -- they were all coming out way too purple. Our color expert helped us change the cyan press curve and it made a big difference. We actually dialed the cyan back about 5% in the midtones and that's giving the pressmen headroom to match that 4/C reflex color.

 

[tmiller_iluvprinting]

If the proofs have not changed, what's changed at press? Are your documented SID's and TVI being achieved at press? SID and TVI become your quality control parameters with G7, if you do not achieve these, or an acceptable range of these, you will not match your proofs. SID and TVI are the first things I measure when there are issues matching the proof, and more times than not there is an issue with the press. Every proof we send out to the pressroom passes qualification or it does not go out. We had a small issue matching proofs made using the GRACol data set, so I used our press data for proofing instead and the issue was solved.

At Rick: I am trying to figure out why you would decrease cyan if your Reflex Blues were too purple? Doesn't make sense.

Regards,
Todd

 

[Lukas Engqvist]

@tmiller decreasing the mid tones means you can increase the SID, by the less is more principle.

@5624GM Paper does affect. Paper at the proofer I found very important factor. (Also other things as temperature and humidity of the room where proofer is, I assume you do regular nozzle checks) Do you have some device to make a reference check to see that the proofer is producing consistent results?

On the press you can usually group papers into categories, but there are some stocks that just won't fill the norm. If you are suspecting a bad batch, keep your reference stock available, and print some sheets with that to see if it was the stock/batch or if something has changed in the process.
Semicoated (and uncoated) paper will usually give a magenta cast if plates are imaged as for coated.
It can also be that magenta has a bad batch (track your references, and what has changed since).

When you say TVI is that the TVI on plate or on press? TVI that counts is the total on paper! (plate is a way to check that the workflow is normal)

One other area to check is your trapping. If you have a trapping fluctuation there isn't a thing prepress can do about it, it is a press issue.

 

[tmiller_iluvprinting]

I have to wonder what happened to gray balance and the NPDC with the 5% cyan reduction move on the plate? Or was the original G7 calibration run not accurate? We are a G7 Master Printer also and we have never had this issue, in fact the 100% Magenta-100% Cyan overprint is colorimetrically quite accurate.

Regards,
Todd

 

[Lukas Engqvist]

@tmiller
Changing the SDI would affect the dotgain. Yes the NPDC would shift if you change the one or the other. But basically for any SDI within the tollerance you can find a corresponding TVI curve to give an acceptable result. This is where the experience comes in, to judge at what SID the best results are given. My judgement would be that either the SID was not optimal to start off (talking of Rickwhiteman's flow) perhapps within tolerance but the trapping values were not optimal? (this is a guess).
There may ofcourse be a number of factors that mean we need to monitor and revaluate our targets and our corrections to obtain those targets.

 

[5624GM]

Thanks Guys, right now it is pointing towards an ink issue.