Where can you purchase printed Gracol targets?

[JoshB]

My Google-fu seems to be weak today; I can't for the life of me find anyone selling hard copies of the ideaAlliance G7 forms. Anyone have a link?

 

[chevalier]

Why exactly would you want to buy one?

 

[JoshB]

Well, I do understand that it's meant to be a tool to help you reach a valid G7 state rather than a check sheet or spectro-photometer calibration tool.

The thing is I'm trying to work with several different printers. In the mix are several different digital color presses, a DI, several different 4-color offset presses, different papers, etc... All the things that G7 is supposed to help you deal with. Everybody claims that they are calibrated, that they are doing it right, but not a single process matches any other, and none of them match my soft proof.

So, while there's obviously a lot of work to do there, it sure seems like it would be helpful to start from "Here's what it ought to look like".

 

[gordo]

Well, I do understand that it's meant to be a tool to help you reach a valid G7 state rather than a check sheet or spectro-photometer calibration tool.

The thing is I'm trying to work with several different printers. In the mix are several different digital color presses, a DI, several different 4-color offset presses, different papers, etc... All the things that G7 is supposed to help you deal with. Everybody claims that they are calibrated, that they are doing it right, but not a single process matches any other, and none of them match my soft proof.

So, while there's obviously a lot of work to do there, it sure seems like it would be helpful to start from "Here's what it ought to look like".

G7 is a method to grey balance output devices - that does not mean that the colors will match across devices. Calibration simply means that a device is brought to a known state - it does not tell you what the color looks (or measures) like.

Idealliance used to sell certified GRACoL 7 press sheets so that printers would have an example of what a press sheet that conforms to ISO 12647-2 looks like. But AFAIK they no longer provide such a reference.

Methinks you need to find out what the different printers you work with are calibrated to. What they likely should be targeting is what's called ISO 12647-2 or GRACoL 7 (which is based on ISO 12647-2 specifications). Then you can use a spectrophotometer to confirm conformance. You also need to confirm that your proofer conforms to ISO 12647-2.

You are diving into deep waters.

best, gordo

 

[JoshB]

Thanks, Gordo. I definitely know just enough to get myself into trouble. What's frustrating is that so many printers don't even seem to know that. I know two large offset printers that didn't even linearize their presses, I'm not sure anyone even understood the concept that you'd have a press profile or reference conditions. They've just got a pressman yanking ink levels back and forth on a per job basis until it "looks right". I really don't understand this industry sometimes.

I'm a software guy writing web-to-print tools. "Upload your file and we'll just take care of it" kind of stuff. I know barely enough about color that when I'm at a production facility, if I'm lucky and have the manuals and instructions right in front of me, I can get things calibrated and get pretty good matches across locations. As soon as I leave we start getting customer complaints and I find that we're weeks out of calibration, or somebody in pre-press changed the automated workflow, or who knows what crap... it amazes me.


Phew. OK. Let me get off my soap box before I trip and fall on my head.

Basically from what I think I understand about the G7 process. The goal is to develop a standard set of reference conditions for a press, paper and screening so that when you run to a set of standard densities you can know that several defined CMYK values will produce a neutral gray. If this is true, then you can reliably expect the overall hue and value of the image ripped through that same process to be very consistent, even on different presses. An individual spot color may not match perfectly, but overall image "A" should look very similar to image "B"; the color balance should be the same, and contrast should end up the same.

For digital presses there doesn't seem to be an effective way to apply the curve-adjustment algorithms (please correct me if I'm wrong). But I'm not sure it matters anyway, because you should be able to use the Gracol Coated profile and the color management of the digital press should do a pretty effective job, producing --again-- not necessarily an exact match but a result that should generally satisfy most customers.

So, I'm looking at trying to develop quality control tools. I already know I'm going to get he-said/she-said push back if I try to compare one printer's output to another. It seems to me like the only way I'm ever going to get a good start is to be able to come in and say "Look. here's an example of a working implementation. This is the standard. Now we're going to iterate through this process until we can achieve something like this, and you're going to make sure that you can keep producing this going forwards."

 

[gordo]

What's frustrating is that so many printers don't even seem to know that. I know two large offset printers that didn't even linearize their presses, I'm not sure anyone even understood the concept that you'd have a press profile or reference conditions. They've just got a pressman yanking ink levels back and forth on a per job basis until it "looks right". I really don't understand this industry sometimes.

Yes, that's often the case. BTW you don't linearize a press (unless you're using the term to mean something different).

Basically from what I think I understand about the G7 process. The goal is to develop a standard set of reference conditions for a press, paper and screening so that when you run to a set of standard densities you can know that several defined CMYK values will produce a neutral gray.

The standard reference condition is ISO 12647-2. If the printer is set up to hit ISO 12647-2 then the G7 method can be used to calibrate the printing process so that it is in grey balance. But if the various printers are not set up to hit a common standard but use G7 to grey balance then you'll have presswork from different printers that are in grey balance but the colors will be different.

If this is true, then you can reliably expect the overall hue and value of the image ripped through that same process to be very consistent, even on different presses. An individual spot color may not match perfectly, but overall image "A" should look very similar to image "B"; the color balance should be the same, and contrast should end up the same.

The key is that the proofs supplied by the different printers should closely match if they are targeting the the same print standard. One then assumes, hopes, and/or prays that the printer can match their own proof. And if your proof is set to the same standard then your proof should be a close match to theirs.

For digital presses there doesn't seem to be an effective way to apply the curve-adjustment algorithms (please correct me if I'm wrong). But I'm not sure it matters anyway, because you should be able to use the Gracol Coated profile and the color management of the digital press should do a pretty effective job, producing --again-- not necessarily an exact match but a result that should generally satisfy most customers.

The ability to do curve adjustments would depend on the workflow and type of digital press. But you're pretty much correct.

So, I'm looking at trying to develop quality control tools. I already know I'm going to get he-said/she-said push back if I try to compare one printer's output to another. It seems to me like the only way I'm ever going to get a good start is to be able to come in and say "Look. here's an example of a working implementation. This is the standard. Now we're going to iterate through this process until we can achieve something like this, and you're going to make sure that you can keep producing this going forwards."

These are the deep waters. For QC purposes you can insist that a color/print control media wedge be included with every proof. That way you can check that proofs from the same printer are consistent and you can compare the proofs of one printer against another to see if they are both targeting the same standard. However, if the printer(s) is not committed to printing to a standard (embodied in their proof) then it is doubtful that they will change to accommodate you unless you are a major customer since their cost to make the change would be significant.

best, gordo

 

[chevalier]

I have a halftone proofer (Fuji/Luxel FinalProof), an inkjet proofer (Epson 9900 with Integrated spectrophotometer) and two printing presses (I'm working on getting Heidelberg's ImageControl certifying/tracking conformance of each press sheet pull) all calibrated to near-GRACoL7 standards (my paperwhite tolerance is <3.5dE rather than <3) and gray balanced via the G7 process. Each device was independently calibrated without reference to the others. Then the two proofs and a press sheet were laid next to each other. The match isn't absolutely perfect but is by far the most accurate and most consistent I've seen achieved. I was very doubtful about this process until I saw it happen and the results it achieved before my own eyes. The trick to maintaining this is certification of conformity - we run a color/print control media wedge on every proof. With digital presses I've heard of running a wedge before and after the job as a means to certify as generally digital work does not accommodate enough excess paper space for a control wedge. On offset printing presses a lack of sheet space problem also occurs but the color bars on the press sheet can be read in via some color control consoles. Logging all of this data in a central database that is easy to access and user friendly is a big obstacle. Fujifilm has made huge inroads into this problem with the Colorpath/Taskero Universe product.

Some informative/useful links:
G7 vs. GRACoL explaination:
Do you know the Difference between GRACoL, GRACoL 7 and G7? | IDEAlliance

Listing of G7 printers and experts:
Master Printer Database - Welcome

Fujifilm's Colorpath/Taskero Universe System:
ColorPath (Taskero Universe) | Consultative Services | Graphic Arts & Printing | Fujifilm USA

 

[JoshB]

OK, now you've got me worried that I've got some really basic misconceptions, Gordo.

Isn't press linearization pretty much step one for any standards process? I want to be able to say 30% and get 30%, right? That seems to be fundamental.

 

[Correct Color]

For digital presses there doesn't seem to be an effective way to apply the curve-adjustment algorithms (please correct me if I'm wrong). But I'm not sure it matters anyway, because you should be able to use the Gracol Coated profile and the color management of the digital press should do a pretty effective job, producing --again-- not necessarily an exact match but a result that should generally satisfy most customers.

Actually, this is pretty far off the mark.

Fact is that what the entire G7 process began as an attempt to duplicate in offset lithography the linearization process that's already included somewhere in the routine of every RIP-driven digital printing device.

Once you're creating dots digitally it's to all that difficult of a process to establish a routine to do some sort of calibration/linearization (the terms loosely used somewhat overlap.)

Of course it's much harder to do on a litho press because of all the variably factors involved, and up until digital plate making, it was pretty much impossible.

But of course now it is possible, but to say it's more difficult to achieve a linear state in a digital device than a litho press has it exactly backwards.

However, the Gracol profile does nothing to achieve linearity or grey balance--it assumes they're already achieved. And understand that color management on a digital device is something that has to be done. It doesn't come in the box from the factory. If you want to attempt to hit a Gracol proofing standard with a digital device, first you have to calibrate and characterize the device, and then you have to send that device images in the Gracol colorspace. How well you do the calibration and characterization will determine how pleased you'll be with the result you get.


Mike Adams
Correct Color

 

[rich apollo]

OK, now you've got me worried that I've got some really basic misconceptions, Gordo.

Isn't press linearization pretty much step one for any standards process? I want to be able to say 30% and get 30%, right? That seems to be fundamental.

Not exactly. One might linearize the platesetter to ensure correct exposure, et cetera. I actually quit linearizing platesetters long ago. I get better results with the natural response of the plates. You must linearize an inkjet proofer before profiling. But, you don't 'linearize' a press.

It sounds like you're operating from the position that dot gain is a bad thing. It's neither good, nor bad, it just is. You can set up your platesetter so that a 30% in the file will yield 30% on press. I've done it, and it looks like crap. Trust me, we like dot gain. Printing without dot gain looks hollow and sharp. I've never ended up using linear plates. Some level of adjustment has always been applied to pull the plate out of linearity.

If you look at the ISO 12647-2 TVI curves and/or the G7/GRACoL NPDC, none of them are 'linear'. They all exhibit non-linear responses. What you're attempting to do is get your presses' dot gain responses to align with the dot gain of the standard you want to match.

 

[rich apollo]

Fact is that what the entire G7 process began as an attempt to duplicate in offset lithography the linearization process that's already included somewhere in the routine of every RIP-driven digital printing device.

I disagree, Mike. The G7 process attempts to control a press in the same manner that you would a scanner. Maybe I'm being pedantic. If it seems I'm hair-splitting, I apologize. RIPs don't generally have a process to correct, or adjust, gray balance, and that's a fundamental part of scanning and G7 calibration.

Once you're creating dots digitally it's to all that difficult of a process to establish a routine to do some sort of calibration/linearization (the terms loosely used somewhat overlap.)

I think it's very important to distinguish between the two terms. "Calibration" is the process of setting up output parameters. "Linearization" is the process of setting those output parameters to a straight-line response of some sort - for example, getting a 30% file value to measure a 30% on the plate. "Linearization" is a more restrictive term, and falls under the umbrella of "calibration".

Of course it's much harder to do on a litho press because of all the variably factors involved, and up until digital plate making, it was pretty much impossible.

In the days of matchprints, the proof was directly tied to the film. 3M, then Imation, then Kodak, engineered the donor sheets to exhibit a TVI response. Divorcing proofing from the final output granted us great freedom to manipulate the appearance of each. Now we can optimize the proof and the plate separately.

And understand that color management on a digital device is something that has to be done. It doesn't come in the box from the factory. If you want to attempt to hit a Gracol proofing standard with a digital device, first you have to calibrate and characterize the device,…

On this I agree completely.

 

[JoshB]

Not exactly. One might linearize the platesetter to ensure correct exposure, et cetera. I actually quit linearizing platesetters long ago. I get better results with the natural response of the plates. You must linearize an inkjet proofer before profiling. But, you don't 'linearize' a press.

It sounds like you're operating from the position that dot gain is a bad thing. It's neither good, nor bad, it just is. You can set up your platesetter so that a 30% in the file will yield 30% on press. I've done it, and it looks like crap. Trust me, we like dot gain. Printing without dot gain looks hollow and sharp. I've never ended up using linear plates. Some level of adjustment has always been applied to pull the plate out of linearity.

If you look at the ISO 12647-2 TVI curves and/or the G7/GRACoL NPDC, none of them are 'linear'. They all exhibit non-linear responses. What you're attempting to do is get your presses' dot gain responses to align with the dot gain of the standard you want to match.

In linearizing my goal isn't to directly make the output look a certain way, but rather to be able to control what that output should be. You get your input PDF already in terms of how how a certain press should respond, whether that's as "SWOP" or "Gracol" or whatever. But if I'm going to emulate any of those characteristics on my press, then step one is understanding the actual characteristics of my press, right?

Sure I could just leave it alone and say "Well, I'm running an offset press, that should be kinda like the theoretical offset press used for SWOP standards. I should be OK, then." And yeah that would kind of work, but if I want to do better than "kind of" I've got to actually understand the true response of my press so I can compensate for the differences between it and the theoretical press.

 

[gordo]

In linearizing my goal isn't to directly make the output look a certain way, but rather to be able to control what that output should be. [SNIP] But if I'm going to emulate any of those characteristics on my press, then step one is understanding the actual characteristics of my press, right?

Sure I could just leave it alone and say "Well, I'm running an offset press, that should be kinda like the theoretical offset press used for SWOP standards. I should be OK, then." And yeah that would kind of work, but if I want to do better than "kind of" I've got to actually understand the true response of my press so I can compensate for the differences between it and the theoretical press.

Rich has explained it well.

You do not need to linearize your plates in order to understand the response of your press.
If you linearize your press response you actually mask its response.
When a CtP device is calibrated the exposure and processing is set to provide a robust ink accepting dot on the plate and a clean non-printing image area. It will also be free of artifacts such as laser swath banding. Once calibrated the plate is not likely to be linear.
That non-linear plate will have a certain tone response on press when the press is run to the appropriate SIDs (or Lab values).
That tone response (among other things) will tell you how well the press is transferring ink.
It will also give you the information you need to build a tone reproduction compensation curve that will be applied to the plate in order for the plate to generate the desired tone response on press. The desired press tone response is probably going to be the ISO 12647 standard - which itself is not linear.

BTW, SWOP is not a press standard. It is a specification for the inputs (e.g. proofs) destined for heatset web presses.

best, gordo

 

[Alois Senefelder]

An - Inkling !

An - Inkling !

Gentlemen,

Tone Reproduction

A PDF - I hope you will find of interest and value - BUT

It might muddy the water - !




Regards, Alois

 

[gordo]

Gentlemen,

Tone Reproduction

A PDF - I hope you will find of interest and value - BUT

It might muddy the water - !

Regards, Alois

Interesting but very confusing if you follow the instructions. It starts by saying that you pick a point on the curve in quadrant 1 and then draw a line horizontally to the curve in quadrant 4. Well, if you draw a horizontal line from quadrant 1 - it can never touch the curve in quadrant 4 so you're stumped from the beginning.

That being said, I think the principle might be akin to the explanation of how to build press curves explained here:

Quality In Print: The principle of dot gain compensation plate curves

best, gordo

 

[JoshB]

Hmm... interesting instructions. I have to agree with Gordo though that something appears funny. Either the description is a bit off or someone has gone and relabeled the Quadrants.

It does show the idea, though, except that this is a bit old-school. It looks like the instructions are intended to help someone deal with photo-negative reproduction from an original hard-copy. Largely the same sort of problems I think, but at the same time not quite the same thing; extra steps one way, missing considerations another.

I'm kind of thinking that everybody here is basically saying the same, thing, and that most of the smoke is a matter of terminology. I'm suspecting that the term "linearization" maybe has some meanings I'm not aware of.

I do prefer to think of things that way, though. It seems easier to me to think of a the press as a linear device, and consider the delta between linear and the theoretical dot-gain curves for a profile, rather than to try to think of two separate curves and the deltas between them. If there's a problem with that, I don't understand it.

I'm not actually having such big issues with getting a decent color match; it's more keeping a good color match when my back is turned that's been challenging.

Are there any really excellent color management books out there? Theory, and best practices? What little I do know basically comes from the PDF spec, RIP manuals and the frequently contradictory online tutorials.

 

[gordo]

[SNIP]

I'm kind of thinking that everybody here is basically saying the same, thing, and that most of the smoke is a matter of terminology. I'm suspecting that the term "linearization" maybe has some meanings I'm not aware of.

I do prefer to think of things that way, though. It seems easier to me to think of a the press as a linear device, and consider the delta between linear and the theoretical dot-gain curves for a profile, rather than to try to think of two separate curves and the deltas between them. If there's a problem with that, I don't understand it.

Not to put too fine a point on it, however it is important that terminology is used correctly (or defined when used) otherwise comments are easily misunderstood - especially for those whose first language is not English.

The terms calibration and linearization do not mean the same thing - especially in a CtP workflow - so they shouldn't be used interchangeably.
A press is not a linear imaging device.
What is important is that a specific tone request in the original file results in a specific tone measured on the presswork. E.g. Where I ask for 50% in my file it should measure 64% in the presswork. If one is printing to a published standard like ISO 12647-2 then the required final presswork tone values are specified for the tone range for each color. So, I know what tones are requested in the original file and I know what tones the calibrated but non-linearized plate delivers on press and with those two data points I can build a tone reproduction curve to be applied to the plate that will map the requested tone values in the file to tone values on the plate that will create the required tone values in the press work. It's very simple and straightforward. Linearization and ICC profiles are not involved.

best gordo

 

[Correct Color]

I'm kind of thinking that everybody here is basically saying the same, thing, and that most of the smoke is a matter of terminology. I'm suspecting that the term "linearization" maybe has some meanings I'm not aware of.

Yeah, that's pretty much it. Actually of course and as all these guys have said, linearization has one literal meaning...and calibration has another literal meaning. However, in digital printing, 'calibration' has come to usually mean doing a linearization routine.

That's what I meant when I said the two terms have come to be somewhat overlapping.

Since I stay almost exclusively in large and grand format these days I'll certainly defer to Rich and Gordo in their expertise in the nuts and bolts of the litho area, but the point is that by whatever name you call it, the point of all these routines is to get neutrals under control. The issue was always that if you could define the start point as zero, the chroma value of the ink as a constant, your max density as constant, and the paper white as a constant, then if you could define the neutrals consistently, you'd have printing as a true commodity, one printer absolutely indistinguishable from another.

How exciting.

Mainly that's why I stay in large and grand format, where that mentality has yet to take hold.


Mike Adams
Correct Color