4-Color printing lesson for a single or 2/color press

GCR is applied as a % (of black) replacement. Max is 100% - example:
Take 50c/40m/40y (gray) into photoshop and convert to Max GCR - results? 50% Black!
Med is a 50% replacement, leaving some y-m-c there.
Standard deviation is 2% midtone gain.
Max GCR allows for a 4% variation without changing the color!
UCA can be applied as a % to either!
Call anytime 412.889.7643

 

How much UCA does one tend to use

 

Depends whether coated or uncoated.
Total Ink Coverage is around 320 for coated and 240 for uncoated.
You apply UCA as a % but check the TIC.

 

I would like to have values for both.
I will make sure I adjust TIC

 

What about black ink limit?

 

These adjustments are image dependent. You have to check TIC after you apply UCA

 

I am in the middle of running the press with my plates as close to linear as I could get with what I am using.
I am thinking that I am going to measure the dot values for the chart you gave me and make an adjustment curve in photoshop. I can make a dot gain curve and create a profile or I just adjust each image with the curves function. I think I have figured out how I can do it with a dot gain curve in a custom color profile.
I also have a question about my densitometer. I have two. One calibrates itself somehow and one I have to measure the paper and then the solid. They give quite different readings. Can you help me understand this and know which one to use

 

I have done 3 of the 4 colours and my measured values on the sheet with my "somewhat" linear plate are almost what you gave me. Mostly just a few percent + and -. That is with the Vipdens densitometer that you have to zero on the paper and then measure a solid before you start measuring the dot.

 

There should be a setting for the densitometer that is “status T”.
The density readings should be ‘absolute’ (including paper). It should NOT subtract paper for density measurement.

 

Of measuring dot area or dot gain the instrument will subtract paper - that’s correct! Just don’t use the density reading for anything-

 

hmmm,
one densitometer I have ONLY reads density after zeroing to paper. The other one does not.
The first is the one I used. It has a higher reading. When it reads 1.4 the other reads .7
Neither have been calibrated. I do have a freshly calibrated card that I tried both on. The first is fairly close to the calibration values.

 

You can add the paper value to the measurement i.e. (.07 paper + 1.33 reading = 1.40 density

 

So are you saying it is good to have as much UCA as you can without going over the recommended TIC. I think I am starting to understand.

 

Yes-correct! UCA is applied as a %.
It only affects the shadow area - not highlight or mid tones.