Measuring color on press

[DanRemaley]

Make sure you have a color bar that includes Solids, 50% tint of each color, 3/color grey patch next to 50% black. Now you can measure dot gain and 3/C grey balance.
If you set the densitometer to "ALL" filters - you can measure a grey patch and get the V - C- M- Y values. V stands for "Visual" or over all density.
The ideal value would be V=.60 C=.58 M=.58 Y=.58
The 'secret' is to have the C-M-Y values equal, that's grey balance - the 'V' number is how light or dark you are. . one measurement and you know all you need to know about the press sheet control.
Dan 412.889.7643

 

[discountprintingservice]

For anyone interested this is what Dan is talking about. This is a custom bar I made for 2 up portrait presses. It has color bars at the tail of the sheet and cyan, magenta, yellow and black dot percentage control strips plus gray balance and trap/hue bars on the operator and non-operator sides of the sheet. I can run 2 up 8.5x11 or a 11x17 either one with bleed and this custom color control bars on my Ryobi 3302 or ABDick Century 3500.

Best thing I ever did learning to control the gray balance instead of trying to compensate with ink density.

 

[aqazi81]

How do you manage to obtain the grey balance if the live area image need more C,Y or M?

 

[turbotom1052]

How do you manage to obtain the grey balance if the live area image need more C,Y or M?

If your pre press curves are fingerprinted correctly to the press, achieving correct grey balance should not require your images to need more or less of anything. We all know that in the real world this doesn't always happen, BUT.... Ive seen things come consistently close. Time and effort spent fine tuning these curves on a number of different stocks will pay off. Its usually a companies reluctance to tie up the press with non paying work, and further reluctance to not spend the money on the required paper, and outside help that often causes this accurate fingerprinting to be rushed through, and not done correctly.

 

[aqazi81]

But if there is a grey balance patch right behind a lets say heavy magenta image, how will you keep the grey balance patch to remain neutral grey?

 

[discountprintingservice]

Regardless of what any color is anywhere on the sheet, any shade of gray is made up of a blend of cyan magenta and yellow, or onlly black. The black is neutral to begin with, but the cyan, magenta and yellow blends could have a color cast (meaning too much cyan, or two much magenta, or two much yellow) if not printing to grey balance. Grey balance when done correctly removes the casted colors by adjusting your curves in your highlights, midtones and 3/4 tones. This allows you to print to a specific target density for each primary color (CMYK), so if you curves are right with correct dot gains and an adjustment for gray balance, it takes the guess work or "adjustment" away from the press operator of having to dial up or down the density to balance those grays on press. In other words, once done, if your densities are right you are printing to gray balance (no color casts), and if you deviate away from those densities (up or down for any color) then you introduce a color cast. Since things change over time you have to monitor the dot gains and gray balance curve over time as roller pressures changes, new blankets, ctp's calibrations drift, etc, etc. For that reason we run calibration strips shown above on every job in the trim area so we can take these readings to check for any drift at any time either on the plate or on the press sheet and can make an updated adjustment curve as needed to keep everything in check.

 

[turbotom1052]

But if there is a grey balance patch right behind a lets say heavy magenta image, how will you keep the grey balance patch to remain neutral grey?

If your pre press curves are spot on and fingerprinted to the specific press your printing on then any "heavy magenta" image should be arrived at by the dot structure of the image as opposed to the ink film thickness on the rollers. In theory Aquazi, a properly fingerprinted press should always be able to print with the same ink film thickness. This never varying ink film thickness will always allow you to print to pre determined densities. If the densities remain the same, and the pre press curves are correct, then the grey balance should always remain neutral, provided the color patches are imaged correctly. Of course this is all assuming that the press is in good mechanical condition and printing with the same dot gain tolerances as when the press was fingerprinted. This is why fingerprinting is not a one time thing. The best results would come from fingerprinting the press at least once a year.

 

[aqazi81]

As we all know that densities on press are not consistent, if you take hundred sheets from press when the press is stable, there will be small deviation in numbers. Will this effect the grey balance?

 

[turbotom1052]

As we all know that densities on press are not consistent, if you take hundred sheets from press when the press is stable, there will be small deviation in numbers. Will this effect the grey balance?

The better your pre press curves are to the press ,the less effect minor variations in ink density will have on both grey balance and overall color. Pre press curves that are optimized for the particular presses printing characteristics, will almost " fall into color' even with slight variations in ink densities.

 

[aqazi81]

Thanks Turbotom and others for the answers.

 

[turbotom1052]

aquazi,
ever notice how on certain jobs you mount the plates and begin the makeready, and the images almost magically seem to "fall right into color"? We as pressman would love to just pat ourselves on the back and claim to have a mastery of the process. Usually these jobs that just fall right into color, also tend to hold color throughout the run, with very little operator intervention.
Then there are the jobs that require many sheets of spoiled paper, to arrive at at color match that seems to require many compromises. These jobs, once you flip on the counter and begin to run, seem to require constant ink adjustments just to produce a salable product. Its usually after one of these jobs that a pressman may question his skills.
Ive experienced both of these scenarios many times over the many years Ive spent running multicolor presses. The final conclusion Ive come up with is that Im neither Guttenburg himself reincarnated, nor am I lacking in skills that particular day when things aren't so easy.
It would only take a short time working in a pressroom environment where the PROPER pre press curves are consistently applied to the plates, before you came to the conclusions I've reached.
This is not meant to make small the accomplishments of a true craftsman, nor is it meant to blow a bunch of smoke up anyones ***, in saying that they are Gods gift to printing. Its instead meant to illustrate the importance of regular calibrations to the process from beginning to end.
For the bean counters that may be reading this post, its my hope that you too can see the value in proper calibration, in spite of the perceived high cost and inconvenience.
For all front line (pressman) who can relate to what I'm talking about, how bout a little help here in getting my point across. Being I am retired from the industry I have no skin in the game, other than to make things a little easier for all parties, not just pressroom employees.
For the employers that have spent the time and resources to fine tune the process kudos to you.

 

[aqazi81]

Agree with you turbotom.
But unfortunately majority here are bean counters.