how to check printer consistency

[Dario]

Hi all,
I don't know if this forum section could be the right place, but I'll try...
I'm not a press operator but a prepress one, so I'm guessing how to check the press quality (besides dot gain & curves AND - above all - besides the press operator who tells me that everything is OK!).
One things that comes in mind is: what about printing a whole sheet of gray control strips and performe random checks, just to control if it prints consistently?
Could it be good?
Thank you all!

 

[Alois Senefelder]

Hello darioluca,

You need to conduct 1) Press Test Forme check. also print down in a waste area margin - 2) Print Control Strip (FOGRA) on ALL print production runs.


Regards, Alois

 

[Schnitzel]

Define what you mean by "prints consistently": is it across the sheet (uniformity), or between sheets in a print run? I'm guessing you mean the latter, but I'm asking just to make sure.

In addition to what Alois wrote, if you aim for an in-house, custom test, you need to choose a measurement instrument, which in turn defines the units of measurement and type of target:
If you are using a densitometer, the results are in the density scale and you can measure primary or secondary colors.
If you are using a spectrophotometer or colorimeter, the results are in CIELab, and you can measure any color combination.

Set the reference values for the test - what you aim for in every color patch.

Set the tolerances that will indicate a test has passed or failed. If using density, choose the largest deviation allowed. If using CIELab, you can choose, for example, the maximum delta-E and an average etc.

 

[Dario]

Hello darioluca,
You need to conduct 1) Press Test Forme check. also print down in a waste area margin - 2) Print Control Strip (FOGRA) on ALL print production runs.
Regards, Alois

What i really meant was mainly to check the quality and consistency in the single sheet - not in the long run - to be sure there are not 'errors' in different areas of it, from bottom to top, or from left to right.
As long as there is uniformity in the single sheet then we can adjust things about dot gain etc.

 

[Alois Senefelder]

Hello darioluca,


I'm puzzled by your reply ........ BUT read the PDF

Regards, Alois


View attachment Print Analysis Procedure005.pdf

 

[Schnitzel]

Fogra has the M-Score method to test for uniformity across the sheet - look it up. It's meant for toner-based digital presses but might give you a meaningful result. You basically cover the sheet with patches of a single gray combination, measure the patches using a spectrophotometer, and use Fogra's formula to calculate the "M-Score", which correlates with how the human eye perceives inhomogeneities in a large color area. They also specify a scale for the possible scores.

Another method might be to cover the sheet with a control strip such as Fogra's, measure the CIELab of all patches, calculate the average CIELab of every patch in the strip and then the delta-E of every patch to those averages. This can show you a visual map of problematic areas in the print.

 

[Deleted member 16349]

What i really meant was mainly to check the quality and consistency in the single sheet - not in the long run - to be sure there are not 'errors' in different areas of it, from bottom to top, or from left to right.
As long as there is uniformity in the single sheet then we can adjust things about dot gain etc.

With offset there are issues with what you are wanting to obtain. A single printed sheet will probably not be consistent in every location on the sheet. This is due to how the roller train manages ink films on its form rollers. Inking a plate, takes ink off the form rollers and the patterns of this loss of ink are not fully made uniform by the addition of new ink before the next cycle of inking the plate. So the situation is that the plate is not normally inked uniformly. This will affect dot gain differently in different locations. So it is the image itself and the design of the roller train that have some affect on the consistency of the printed sheet. This also means that there is no specific finger print of how the press prints because it is affected by the image being printed.

The Anicolor press gets around this problem because in principle, it inks the plate consistently in all locations.

If you are looking for perfection of consistency in the printed sheet, you probably will not get it. If you can accept that there will be some variation and live with it, then it might lead to a bit less frustration.

 

[Dario]

If you are looking for perfection of consistency in the printed sheet, you probably will not get it. If you can accept that there will be some variation and live with it, then it might lead to a bit less frustration.

Thank you, that's nice!
Of course I can live with that!! ​​​​​​​I simply need to know it first.

I was just trying to figure out how much I could expect from the press machine itself.

 

[Dario]

Fogra has the M-Score method to test for uniformity across the sheet - look it up. It's meant for toner-based digital presses but might give you a meaningful result. You basically cover the sheet with patches of a single gray combination, measure the patches using a spectrophotometer, and use Fogra's formula to calculate the "M-Score", which correlates with how the human eye perceives inhomogeneities in a large color area. They also specify a scale for the possible scores.

Another method might be to cover the sheet with a control strip such as Fogra's, measure the CIELab of all patches, calculate the average CIELab of every patch in the strip and then the delta-E of every patch to those averages. This can show you a visual map of problematic areas in the print.

So mine was not a so bad idea!

 

[Dario]

Thank you all people!

 

[gordo]

It's a good idea to check the integrity of the presswork before you do any measuring. And for that you should use a USB camera microscope.
Also you need to have defined a print condition standard, the specifications that support your standard, and the associated tolerances.

 

[Dario]

Just found this: https://www.fogra.org/index.php?menuid=35&getlang=en

...and also this: https://fogra.org/index.php?menuid=218&reporeid=221&getlang=en
where you can download some "Uniformity test forms" to print.

Only Fogra knows how to use them