G 7 certification

gordo

Well-known member
How important is color certification to your customers, and is G7 worth it?
For some corporate buyers G7 certification is important - even if they don't understand what that means. The majority of print buyers would be clueless.
The important thing is that you, as a print supplier, have at least one appropriate print standard, with supporting specifications, that you can reliably adhere to and that your proofing is aligned to it.
 

Correct Color

Well-known member
Bobk,

It really depends. What G7 is -- and all it is -- is a calibration procedure. Initially, it was developed for offset lithography, because it had been a bedevilment in that industry prior to computer-to-plate that there was no way to anticipate neutral tone curves on analog-generated plates. So each individual printer had pretty much their own closed-loop color system.

However with the arrival of computer-to-plate, it became possible to control neutral tone curves on plates, and in essence, that's what G7 attempts to do.

But that's all it does. End of story. Nothing else.

The idea became that since in lithography everything had become all about standards, and since there were standards for media white points, chroma values for ink, and densities for ink, that if you could determine tone value calibrations for a given set of standard parameters, then you'd need no individual ICC profile for that condition; a stock ICC profile built with those calibration values as its expected tone curves would work in all cases in that standard condition; i.e., Gracol or SWOP profiles.

And again, that's it. There's no more that G7 does.

So if that's what you're doing, then yeah, it has some benefit.

But if that's not what you're doing, it has none at all.

The important thing to remember is that unless you have standard conditions, then whether your calibration is some RIP-standard calibration routine or G7, that calibration is only a calibration; it's just a part of the machine state you must characterize with an ICC profile.

And it's the profile that carries the load. Not G7.


Mike Adams
Correct Color
 

gordo

Well-known member
@CorrectColor
On a sidebar, a benefit of going through the G7 experience is that many printers are exposed to the idea of process control in print production. Assuming that the G7 expert is knowledgeable and educates the printer appropriately.
 

pauly92

Well-known member
Bobk,

It really depends. What G7 is -- and all it is -- is a calibration procedure. Initially, it was developed for offset lithography, because it had been a bedevilment in that industry prior to computer-to-plate that there was no way to anticipate neutral tone curves on analog-generated plates. So each individual printer had pretty much their own closed-loop color system.

However with the arrival of computer-to-plate, it became possible to control neutral tone curves on plates, and in essence, that's what G7 attempts to do.

But that's all it does. End of story. Nothing else.

The idea became that since in lithography everything had become all about standards, and since there were standards for media white points, chroma values for ink, and densities for ink, that if you could determine tone value calibrations for a given set of standard parameters, then you'd need no individual ICC profile for that condition; a stock ICC profile built with those calibration values as its expected tone curves would work in all cases in that standard condition; i.e., Gracol or SWOP profiles.

And again, that's it. There's no more that G7 does.

So if that's what you're doing, then yeah, it has some benefit.

But if that's not what you're doing, it has none at all.

The important thing to remember is that unless you have standard conditions, then whether your calibration is some RIP-standard calibration routine or G7, that calibration is only a calibration; it's just a part of the machine state you must characterize with an ICC profile.

And it's the profile that carries the load. Not G7.


Mike Adams
Correct Color

Hi Mike,

does this mean, for example in Onyx (x21.1) i could create a media profile by doing the ink restrictions, linearization and then G7. Then use a standard profile like a Gracol? as the ICC profile?
does that mean that profile will print to Gracol standards?

Not something i plan to do, nor do i have the time to toy with it or use G7. Just wondering why it's in onyx and how it could be used.
 

Correct Color

Well-known member
Pauly,

No. It does not mean that. That's the problem.

Think of making a profile. First you have variable elements which you have to define, and among them are your actual primary color values, your actual densities of each colorant, and your total of all colors.

In addition, of course, you have the media white point.

The original point of G7 was that in offset lithography, there are standards for each of the these elements. So theoretically, if you knew them all, and recreated them all correctly, then all you'd need to have a profile that would work across devices is a "tone curve" or "calibration" or "linearization" or whatever you want to call it, that describes the neutral print density characteristics of a particular press.

Of course, prior to computer to plate, that was simply not feasible to determine.

However, with the advent of computer to plate, it became possible. And that's what G7 is.

Regardless of what they say, it isn't anything else.

So in order to print to G7 spec using a Gracol profile, you must be using a media with the white point specified in that profile, and the individual primary color values and densities specified in that profile, and of course the total of all colors specified in that profile as well.

Which, of course, in large format printing, does not happen.

And since it doesn't happen, once you've defined your tone curves by whatever method, you've got to make an ICC profile... and once you do that, it's not G7 anymore.

Why does Onyx include it?

Because Idealliance and Nazdar have done such a good job selling it.



Mike
 

gordo

Well-known member
So in order to print to G7 spec using a Gracol profile, you must be using a media with the white point specified in that profile, and the individual primary color values and densities specified in that profile, and of course the total of all colors specified in that profile as well.

For clarity, I believe that the G7 method ignores densities.
 

alibryan

Well-known member
For clarity, I believe that the G7 method ignores densities.
Densities play an important part in the certification process, and are preferably established first. Then individual curve adjustments are made from there.
 

gordo

Well-known member
Densities play an important part in the certification process, and are preferably established first. Then individual curve adjustments are made from there.

Then they must have changed their methods. Originally they wouldn't publish SID targets but only target Lab values. The intent was for the printer to hit the Lab values. If the printer wanted to measure the SID values once they hit the Lab values then that was their prerogative but wasn't in the G7 spec.

Can you provide a link to G7's target solid ink densities?
 

alibryan

Well-known member
I think we’re talking about the same thing only the SIDs are usually already established at a shop for a particular ink. The first measured pulls for the certification may want to move those numbers a little bit, but since it’s important to have SIDs that are good for both solids as well as screens, it’s preferable to try and do as much adjustment as possible using only the curves.
 

gordo

Well-known member
I think we’re talking about the same thing only the SIDs are usually already established at a shop for a particular ink. The first measured pulls for the certification may want to move those numbers a little bit, but since it’s important to have SIDs that are good for both solids as well as screens, it’s preferable to try and do as much adjustment as possible using only the curves.
I agree that the SIDs are usually already established at a shop for a particular ink. That is also what G7 says that you should start with.
However, that does not mean that the shop's SID values are valid or appropriate or are a target. They are just to get the press up and running ("Just start up as you always do."). Lab values are what G7 is actually concerned with.

What G7 says is:

"Since 2006, neither GRACoL® nor SWOP® nor G7® have specified solid ink densities or TVI (dot gain) values. Legacy solid density or TVI values are no longer valid.
To find YOUR target solid ink densities, first achieve the closest solid Lab values possible, then switch the instrument to density and record your particular values."

It can be confusing.
 

pauly92

Well-known member
Pauly,

No. It does not mean that. That's the problem.

Think of making a profile. First you have variable elements which you have to define, and among them are your actual primary color values, your actual densities of each colorant, and your total of all colors.

In addition, of course, you have the media white point.

The original point of G7 was that in offset lithography, there are standards for each of the these elements. So theoretically, if you knew them all, and recreated them all correctly, then all you'd need to have a profile that would work across devices is a "tone curve" or "calibration" or "linearization" or whatever you want to call it, that describes the neutral print density characteristics of a particular press.

Of course, prior to computer to plate, that was simply not feasible to determine.

However, with the advent of computer to plate, it became possible. And that's what G7 is.

Regardless of what they say, it isn't anything else.

So in order to print to G7 spec using a Gracol profile, you must be using a media with the white point specified in that profile, and the individual primary color values and densities specified in that profile, and of course the total of all colors specified in that profile as well.

Which, of course, in large format printing, does not happen.

And since it doesn't happen, once you've defined your tone curves by whatever method, you've got to make an ICC profile... and once you do that, it's not G7 anymore.

Why does Onyx include it?

Because Idealliance and Nazdar have done such a good job selling it.



Mike
Thanks for the great explanation Mike,

G7 is definitely not in my industry, And can't see why it needs to be.

Enjoy - Hope to see more videos on your youtube channel.
 

Correct Color

Well-known member
Gordo,

You are absolutely right. I used the word "densities" inadvisedly. The proper term might more be "value" or "L*a*b* value." Or just "the same color as is the primary value in the color space you wish to use this file as calibration for."

You and my wife would get along famously.


Mike
 

jstill

Member
For us we get more effective "printing to the numbers and easier press to proof match. Good grey balance without the guess work. We also do not need custom press profiles.
 

gordo

Well-known member
For us we get more effective "printing to the numbers and easier press to proof match. Good grey balance without the guess work. We also do not need custom press profiles.
What was your process before?
 

phapp

New member
So in order to print to G7 spec using a Gracol profile, you must be using a media with the white point specified in that profile, and the individual primary color values and densities specified in that profile, and of course the total of all colors specified in that profile as well.
Are you familiar with SCCA? In order to pass G7 Colorspace GRACoL, you do need to hit the tolerances as defined by the specification for GRACoL. However, G7 does allow you to apply Substrate Corrected Color Aims. What this does is re-adjusts the aims for Solids and Colors based on the white point of the paper.
 

danremaley

Well-known member
Pauly,

No. It does not mean that. That's the problem.

Think of making a profile. First you have variable elements which you have to define, and among them are your actual primary color values, your actual densities of each colorant, and your total of all colors.

In addition, of course, you have the media white point.

The original point of G7 was that in offset lithography, there are standards for each of the these elements. So theoretically, if you knew them all, and recreated them all correctly, then all you'd need to have a profile that would work across devices is a "tone curve" or "calibration" or "linearization" or whatever you want to call it, that describes the neutral print density characteristics of a particular press.

Of course, prior to computer to plate, that was simply not feasible to determine.

However, with the advent of computer to plate, it became possible. And that's what G7 is.

Regardless of what they say, it isn't anything else.

So in order to print to G7 spec using a Gracol profile, you must be using a media with the white point specified in that profile, and the individual primary color values and densities specified in that profile, and of course the total of all colors specified in that profile as well.

Which, of course, in large format printing, does not happen.

And since it doesn't happen, once you've defined your tone curves by whatever method, you've got to make an ICC profile... and once you do that, it's not G7 anymore.

Why does Onyx include it?

Because Idealliance and Nazdar have done such a good job selling it.



Mike
So here’s a little ‘history’ of color reproduction. In the ‘old days’ we had ‘trade houses’ which produced color separations for the printers. I was one of those - so how did we know how to make the separation’s?
We made them all to SWOP - (Specifications for Web Offset Publications) - based on 133 line screen Web printing. It worked great for Sheetfed at 150 line too. We produced film that was linear and the press room pushed or pulled ink to get the color (and gray balance correct). We could have “curved” the film to adjust for press conditions but the printers never measured there print characteristics.
GATF did a lot of research on press characteristics, including SID, dot gain, print contrast, grey balance, etc.
I measured a “Good” sheet, adjusted for grey balance, printed at SWOP densities. I have all the dot area numbers for the complete tone scale - making a grey balanced sheet! Highlight to Shadow! Using ISO inks.
E-mail me and you can try my method -
At the RIP you create a file for “measured” sheet. Use my numbers for the “WANTED” values. The RIP will do the adjustment.
Funny how the RIP’s have a “WANTED” file but NO ONE has these values? Until now!!
danremaley@comcast.net
412.889.7643
 

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