|
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
|
