Press fingerprinting: SID absolute or relative

[Tarun Chopra]

Hi,

I plan to do a press fingerprint should I read absolute density or relative density for the sake of consistency in densitometric readings?

Any suggestions would be of great help.

Thanks

 

[gordo]

Hi,
I plan to do a press fingerprint should I read absolute density or relative density for the sake of consistency in densitometric readings?

Depends on where you are. In North America the standard is Status T/ ANSI T: wide band color reflection densitometer response - absolute density, unpolarized, dry readings.

You can use a T-Ref card ( http://www.printtools.org/colorrefcards/tref_xrite.php ) if you need to align your instruments to a standard reference.

best gordo

 

[meddington]

Perhaps not an outright compelling advantage either way except for aligning with legacy practices of your company, client/colleagues, or standards bodies. And as gordo pointed out that would be absolute for north America. Absolute would also be more aligned with your visual perception.

 

[Alois Senefelder]

Press Fingerprinting

Press Fingerprinting

Hi, a useful PDF


Regards, Alois

 

[rich apollo]

An argument for, and against, relative

An argument for, and against, relative

Theoretically, relative readings would be more "portable" from stock to stock. This is based on a number of preconceptions.

On the other hand, relative would require the pressmen to calculate target values for each stock. Might have trouble with buy-in.

 

[gordo]

Theoretically, relative readings would be more "portable" from stock to stock. This is based on a number of preconceptions. On the other hand, relative would require the pressmen to calculate target values for each stock. Might have trouble with buy-in.

Density is measured absolute and not relative for several reasons:
1 The color of the paper is all the color we see when viewing presswork (ink just filters the light reflected off the paper).
2 The density of paper under a layer of solid ink is not the same as the density of unprinted paper on the same sheet, therefore, subtracting the paper from the density does not accurately reveal the density of the ink film above. Paper and ink film densities are not additive. (source: GAC)
3) Absolute is the ANSI/ISO requirement

Note also that the backing for measuring press sheets according to ANSI/ISO should be black.
Interestingly, the specification for the backing used for measuring proofs is white.

best, gordo

 

[Deleted member 16349]

Density is measured absolute and not relative for several reasons:
1 The color of the paper is all the color we see when viewing presswork (ink just filters the light reflected off the paper).
2 The density of paper under a layer of solid ink is not the same as the density of unprinted paper on the same sheet, therefore, subtracting the paper from the density does not accurately reveal the density of the ink film above. Paper and ink film densities are not additive. (source: GAC)
3) Absolute is the ANSI/ISO requirement

Note also that the backing for measuring press sheets according to ANSI/ISO should be black.
Interestingly, the specification for the backing used for measuring proofs is white.

best, gordo

my print blog here: Quality In Print

I would say that it is complicated. Statements 1 and 2 are in conflict to some extent.

The simple model of the light going through the ink film to the paper and then reflecting back up through the ink film with some of the light being absorbed or filtered out does not describe what actually happens. Some light is reflected internally in the ink film and relfects back out without getting to the paper at all.

This is splitting hairs but colour is not in the paper. Colour does not exist in Nature. Light does exist and that is the real question. How does the the ink on the substrate affect how light reflects back from the paper and ink film structure. It is not a matter of a perfectly uniform ink film on a perfectly smooth reflective surface. Density is a result of the combination of that ink and that paper.

What one can say is that if one calibrates a specific ink film thickness (amount of ink) to a density for a combination and then develop the change in density to change in ink relationship, then you can move up have a predictable process where you can target any point on the density ink curve. This can only be done with positive ink feed on a press.

 

[rich apollo]

Something interesting about the PDF Alois posted - Gans has G7 certified folks on board and yet they're stating in the document that the ink densities shall be thus and such. Bit of a contradiction.

Don't you guys think Alois posts well for a dead guy?

 

[gordo]

Something interesting about the PDF Alois posted - Gans has G7 certified folks on board and yet they're stating in the document that the ink densities shall be thus and such. Bit of a contradiction.

I believe that GRACoL has moderated their stance on solid ink density. Quoting from the Idealliance Press Operator’s Guide to G7:
"As a first step, the printer should conduct printing trials to determine what wet density target best achieves the ISO colors."

So, solid ink density should give you the proper ink film thickness at which point, if you're using the correct inks, etc. you should be hitting the appropriate CIEL*a*b* values. At the end of the day, the priority is to achieve the CIEL*a*b* values.

best, gordon p

my print blog here: Quality In Print

 

[[email protected]]

Question then: As I look at the G7 NPDC graph paper I notice that a 2% dot should yield about a .02 density. Most of the papers I read have a density higher than this(~.05). So if I add a 2% printing dot on there I'll be well over the suggested .02 more like .07-.09. How do we reconcile this?

Clark

PS The NPDC fan graph paper is printed from the jpg available from ideaalliance so the resolution is fuzzy, but I think I'm reading correctly, no?

 

[rich apollo]

The NPDC is defined using density minus paper.

Go to G7 How To and download the How-To guide. It'll make things clearer.

To Gordo, there's no softening at IDEAlliance about density. Run to the ISO color targets in the calibration run - that's how you find the density you should be at.

 

[[email protected]]

Isn't running the NPDC a major part of "fingerprinting" a press? Which is what the OP was asking about. And then all the replies came back "absolute" for North America, hence my observation;~)

Clark

 

[gordo]

Isn't running the NPDC a major part of "fingerprinting" a press? Which is what the OP was asking about. And then all the replies came back "absolute" for North America, hence my observation;~)

The original question was: "I plan to do a press fingerprint should I read absolute density or relative density for the sake of consistency in densitometric readings?"

There was no mention of NPDC or using the G7 methodology, so those subjects are irrelevant to the original post question. Press fingerprinting was done before G7 and is being done now apart from G7.

To Rich's point: "there's no softening at IDEAlliance about density. Run to the ISO color targets in the calibration run - that's how you find the density you should be at."

That's not what I understand from the Idealliance Press Operator’s Guide to G7: Quote: "As a first step, the printer should conduct printing trials to determine what wet density target best achieves the ISO colors."
That, to me puts the SIDs first with the target priorities ultimately being the ISO colors.
Also, the original question was regarding press finger printing - which, to me, is not the same activity as a "calibration run."

In any case, NPDC and G7 are not topics I would wish to discuss. So I will not be responding any more in this thread to the subject of NPDC or G7.

best gordo

my print blog here: Quality In Print

 

[meddington]

That's not what I understand from the Idealliance Press Operator’s Guide to G7: Quote: "As a first step, the printer should conduct printing trials to determine what wet density target best achieves the ISO colors."
That, to me puts the SIDs first with the target priorities ultimately being the ISO colors.

This is a bit of chicken-or-the-egg thing. Press ops want an idea of what SIDS to start with, ISO Labs are the target, but a 5 delta E tolerance equates a very wide window for SID, so starting and ending with SID makes sense to me, as long as verification of ISO labs is taking place. Ultimately I think Rich and Gordo are talking about the same thing.

In any case, NPDC and G7 are not topics I would wish to discuss. So I will not be responding any more in this thread to the subject of NPDC or G7.

Fine, be that way. Will it be religion or politics then.

 

[Tarun Chopra]

Thanks for all the inputs.

Will it be incorrect to read relative values (minus paper) as paper could influence density values and maintain relative density values across similar coated stock.

Absolute values take paper into consideration because of which there is bound to be difference in density readings between similar paper stocks.

The reason for this approach is that paper itself is the biggest variable and I want to ignore that deveation from my readings. Its like identifying ink film thickness and maintaining that across similar coated stock so that we maintain the target ink film thickness and ignore paper variable..... (hoping) to get similar color reproduction.

Thanks

 

[meddington]

The reason for this approach is that paper itself is the biggest variable and I want to ignore that deveation from my readings. Its like identifying ink film thickness and maintaining that across similar coated stock so that we maintain the target ink film thickness and ignore paper variable..... (hoping) to get similar color reproduction.

Thanks

Paper is indeed a big variable, but what kind of deviations in densities are your seeing that would warrant this?

moreover, reading relative you have to measure the paper first in order for the densitometer to know what density of paper to "omit", so if your paper deviates across the sheet (by significant values), you might have to measure the paper to omit it for every reading across the sheet in order to get comparable "relative" measurements.

More-Moreover...if your paper deviates significantly in density across the sheet, your eye sees this effect (potentially), and measuring absolute would be truer to what your eye sees. So even if your ink film thickness were uniform, you'd still (theoretically) see differences due to the paper deviations.

But really, if your paper's that bad (really?), ever consider switching?

 

[vaithi47]

what gabnsink has given is a starting pointyou have to determine the ink densities which gives you the best contrast/cie L a b values. it is self backing for thicker stocks ,white backing for one side printed thinner stocks and black backing for both side printed thinner stocks