Ink desities on press are very low. WHY?

[racerxnet]

I was not sure if this is the correct sub forum for my question, but here goes. I am a pressman on a Sunday 2000 press with closed loop color capabilities. We print high end, 4 color work 24/7 and continually struggle to print at target densities to match color. As an example, this week the crew ran a job with densities at k-1.50 C-1.05 M-1.0 and Y-.80 average. We are aware that the numbers are to low and ink film thickness in the roller train is very light. In asking management what is going on regarding the dot size and densities, we are told that the image files from the customer is the cause of these discrepancies on press. Other statements are the color gamut G-7 is to wide in comparison to SWOP, and we cannot accommodate certain files from certain suppliers for a color match on press. Here are issues on press I see daily:

The press has been finger printed and ICC profiles are made based on the test, but are not used once there is a color issue on press.

Black ink settings over 1.50 density cause light scumming/tinting in non image areas.

Etch has been changed after fingerprinting the press. No retesting after change

Ink has been changed after fingerprinting the press. No retesting after change

The same ink is used on older Hantcho presses as well as the Sunday presses. Is this a good practice with different water/ink systems. Is the ink formula best suited for each press?




The closed loop color system provides Delta Lab readings as well as others. I don't think anyone has used the tools on press to help better understand and make appropriate changes as needed for better reproduction. What can be done to help move the reproduction process in the correct direction and what order should be first, second and third... Could you please comment on the ink used on press as well as the other points mentioned.

Thanks,

AP

 

[Kaoticor]

Depending on which type of paper you are using, those densities dont seem terribly low... An uncoated paper would be marginally close to the densities you listed with perhaps just a little more yellow.

Yes, the image files could cause problems, there are a lot of variables involved. We have used the same ink formulation over various web presses in the same print shot with success. From my personal experience, I have not seen to many detriments of using the same ink, but that is just an opinion. Your Hantcho uses a brush dampening and the Sunday uses a continous dampening, is that right? We have used the same ink across both a brush and continuous dampening here personally.

If you are getting a lot of color shift and struggling you need to look at a few key points:

Are you getting a lot of color shift within the same job or from job to job ???
Do you notice color shift as the press heats up?
You said black ink settings over 1.5 density cause light scumming / tinting in non image areas. Should probably look in to that
Are you able to provide a close match to your contract proof by adjusting densities, or does it not seem right no matter what you do?

I'm sure others will have helpful feedback more on the pre-press end of it as well.

-K

 

[Prepper]

Sounds like color management is lacking on the front end? In-coming files can be normalized and brought into a common profile that your press is capable of printing at it's normal target densities, whatever those were when the fingerprinting and profiling were done. Sounds as if you have all the right tools on the press side to keep things consistent but the plates (files) you're being given to print are varying.

Just been going thru this here from the other direction, files and plates are consistent, press is not. Either way you'll be chasing color and making compromises to get as close as you can to the proof and using your eyes and judgement to do that when you have all those tools to measure and set things with.

Constantly moving targets are hard to hit, no matter where they are happening.

 

[gordo]

I am a pressman on a Sunday 2000 press with closed loop color capabilities. We print high end, 4 color work 24/7 and continually struggle to print at target densities to match color. As an example, this week the crew ran a job with densities at k-1.50 C-1.05 M-1.0 and Y-.80 average. We are aware that the numbers are to low and ink film thickness in the roller train is very light. In asking management what is going on regarding the dot size and densities, we are told that the image files from the customer is the cause of these discrepancies on press. Other statements are the color gamut G-7 is to wide in comparison to SWOP, and we cannot accommodate certain files from certain suppliers for a color match on press.

There's a few issues here.

There are usually two things you're trying to do, they're related but can be dealt with separately.

1) Tone reproduction. This refers to the reproduction of tones through the scale from 100% to 0%. If you're running your SIDs low to better reproduce the tone range (i.e. dot gain) then you will compromise your color gamut and put the press in an unstable running condition with subsequent litho problems like blinding, scumming, etc. You should be able to run your press at or near standard (SWOP) SID targets. Which are (KCMY sequence):
Grade # 1-2 Coated 1.70 1.40 1.50 1.05
Grade # 3-4 Coated 1.60 1.30 1.40 1.00
Grade # 5 Coated 1.60 1.30 1.40 1.00
Press tone reproduction is best dealt with by applying a dot gain compensation curve to the plate. That compensates for any issues in tone reproduction caused by the SIDs that you need to run to. If customer supplied files are relatively consistent (which they usually are since most people use PhotoShop defaults when converting from RGB to CMYK) then the plate curve should be able to handle this problem. The other solution is to employ a reseparation workflow that takes in customer files and reseparates them so that they all now represent a common standard. I.e. the customer files are normalized to the appropriate print standard.

2) Color reproduction. This refers to the color your press delivers relative to the standard (e.g. SWOP or ISO 12647-X) that you are trying to hit. Color reproduction is affected by the choice of ink hues you use and the SIDs that you run to. If your SIDs are too low then your gamut is reduced and your overprint ink trapping is less efficient which in turn can reduce your gamut as well as skew your colors.

G-7 is not a specification. It is a method for grey balancing an output device. What your manglement needs to do is to put in the proper systems that allow you to align to an industry specififation - ISO 12647-x

Here are issues on press I see daily:

The press has been finger printed and ICC profiles are made based on the test, but are not used once there is a color issue on press.

IMHO That's a bit backwards. You need to have an industry specification (i.e. ISO 12647-x) as your target. An ICC profile representing that specification is used to make your proofer output proofs that represent that target. Then you choose ink hues and apply plate curves to align your press output to that proof.

Black ink settings over 1.50 density cause light scumming/tinting in non image areas.

That should be investigated as there are many reasons for that.

Etch has been changed after fingerprinting the press. No retesting after change

Ink has been changed after fingerprinting the press. No retesting after change

All shops should have a golden reference standard. I.e. presswork, proof and prepress data that represents the print condition when everything was working correctly. Make a change? Then rerun the golden reference to measure the impact and make any needed adjustments.

The same ink is used on older Hantcho presses as well as the Sunday presses. Is this a good practice with different water/ink systems. Is the ink formula best suited for each press?

It's quite possible that one ink formula will work with both. You need to do the tests.

The closed loop color system provides Delta Lab readings as well as others. I don't think anyone has used the tools on press to help better understand and make appropriate changes as needed for better reproduction. What can be done to help move the reproduction process in the correct direction and what order should be first, second and third... Could you please comment on the ink used on press as well as the other points mentioned.

1. define the target for the presswork (ISO ISO 12647-x)
2. align the ink hues to that target
3. create proofs that represent that target
4. run test forms on press at the appropriate SIDs
5. measure the CIE Lab values of your primaries and secondaries to see how they align to the specification
6. adjust SIDs to tighten the alignment
7. if SIDs deviate more than about 10 points to get a better alignment or if alignment cannot be achieved then adjust ink hues as required.
8. check tone reproduction at the final SIDs. Build plate curves as required.
9. run on press and confirm color and tone reproduction - adjust as required.
10. document the results and file for reference.

best, gordo

 

[racerxnet]

2. align the ink hues to that target

Are you referring to the ink hues in the proofing process?

 

[gordo]

Are you referring to the ink hues in the proofing process?

No. I mean the press inks.
The proofer's color output is adjusted by the ICC profile that drives it.

Best, gordo

 

[BeauchampT]

Just a comment on running brush and continuous dampening with same inks...it works, but, so do some old Gremlins, but nobody wants to drive one.

Getting an ink that is specified for a continuous dampening system will help with dot gains and runnability in the long run.

Also, I would be I inclined to make sure that you have a measurement device that isn t part of the press system (a separate unbiased device)

 

[rich apollo]

racer,
The ink and water on this press are not mechanically linked; they have separate electronic controls. Part of what you're describing sounds like the "water curve" is not set correctly.

Is scumming the only reason that the inks are being run down? Are you fighting dot gain? That could be a simple plate curve adjustment.

Third thing, as Prepper suggested, you could "normalize" the incoming files.

<In asking management what is going on regarding the dot size and densities, we are told that the image files from the customer is the cause of these discrepancies on press. Other statements are the color gamut G-7 is to wide in comparison to SWOP, and we cannot accommodate certain files from certain suppliers for a color match on press>

None of these are acceptable comments, in my opinion. Supplied files can be made to work. Prepress has to seize control of the files, and management has to provide them the tools with which to do it.

 

[Lukas Engqvist]

Prepress cannot in any way affect the solid primaries and secondaries.

Dot gain can needs to be established as a jonint agreement between prepress and press since it depends on press conditions and plate curves. To some extent prepress can help manouvre fluctuations in press conditions (such as blanket wear problems etc) But the press should be documented so that it can be reset at optimal working order. A press can to very rarely compensate for problems with plate curve, CTP or developer.

Prepress is alone responsible if there is variance in colour between images on the same sheet (one image too low contrast next to a too high contrast image), and this ought to be visible in a proof. Since the proof should be showing what you are able to achieve, the management would be able to refer to the proof, and forewarn the customer of any limitations in vibrance due to colour gamut miss-matches etc). If you cannot predict your result, what is the point of the proof?

Once you know your process then it would be possible to point fingers in the rare occasion there is a problem with the batch of paper or ink. In sheet press the paper being the problem is easily tested by printing on other stock. If you have records of normal plates, you can easily find out that plates are normal.

 

[gordo]

Prepress cannot in any way affect the solid primaries and secondaries.
[snip]

Dot gain can needs to be established as a jonint agreement between prepress and press since it depends on press conditions and plate curves. To some extent prepress can help manouvre fluctuations in press conditions (such as blanket wear problems etc) But the press should be documented so that it can be reset at optimal working order. A press can to very rarely compensate for problems with plate curve, CTP or developer.[snip]

The problem is that in most shops there is a disconnect between prepress and pressroom. And press operators don't always understand how prepress can help them. So, if there is too much dot gain the press operator might lower SIDs to compensate, or switch to a higher tack ink instead of talking to prepress about how they can help bring things into alignment with plate curves.

Dot gain is not the issue. The issue is tone reproduction. (You can have very different dot gains while achieving the final tone reproduction curve.) That is established by management when they decide what print characteristic they want to align to and sell. Then prepress working with the pressroom implement procedures to enable the shop to achieve the desired print characteristic.

best, gordo

 

[Lukas Engqvist]

Thanks Gordon, I sometimes fall into talking about dot gain when I mean TVI.

 

[gordo]

Thanks Gordon, I sometimes fall into talking about dot gain when I mean TVI.

Dot gain and TVI are the same thing. TVI is just a more accurate way of saying it.
What I was referring to is tone reproduction - or tone curve.
What that means is that for different tones through the scale (from 0% to 100%) you expect specific tone values in the presswork. E.g. When I ask for 50% in the file I expect 66% in the presswork. Because different halftone screens papers and presses have different dot gains, or TVIs - therefore TVI should not be the target. The target should be the final tone in the presswork irrespective of what TVI it takes in order for me to achieve that final tone value.

Best, gordo

 

[Deleted member 16349]

Dot gain and TVI are the same thing. TVI is just a more accurate way of saying it.
What I was referring to is tone reproduction - or tone curve.
What that means is that for different tones through the scale (from 0% to 100%) you expect specific tone values in the presswork. E.g. When I ask for 50% in the file I expect 66% in the presswork. Because different halftone screens papers and presses have different dot gains, or TVIs - therefore TVI should not be the target. The target should be the final tone in the presswork irrespective of what TVI it takes in order for me to achieve that final tone value.

Best, gordo

Both dot gain and TVI are problematic. Personally I still like the term dot gain and only because of the intention but not because of the actual result.

TVI is a problem because the TVI's implies something that one sees but what values are measured for CMY are not visible directly. One measures green for magenta TVI but one does not see green in a magenta screen.

The idea of tone is problematic for these reasons. OK for black ink but not so perfect for CMY.

OK, tone is a practical method to use but not such a scientific method. It is a result of past craft practice.

Why not just measure the colour of printed screens and develop the methods and technologies to do that quickly and easily? Forget dot gains or TVI as a colour management parameter and just use TVI for process monitoring.

No matter what modifications are made to screen curves in prepress, in principle, a press will print the same colour for a given screen set, paper, and ink combination printed at specific densities.

I think things would be so much easier for printers if there would be changes in how these colour management technologies are developed. Something for the future but not so much help for the present. :-(

 

[gordo]

Erik wrote:

Why not just measure the colour of printed screens and develop the methods and technologies to do that quickly and easily? Forget dot gains or TVI as a colour management parameter and just use TVI for process monitoring.

I believe this can be done today with digital presses - but I don't think it is being done.

With a bit of R and D it could be done in offset, however, there is no ROI for the vendor to do the work. There is no, or insufficient, customer (printshop) demand to develop such a solution. I know because I was involved in such a project in the late 90s.

Best gordo

 

[Deleted member 16349]

Erik wrote:

I believe this can be done today with digital presses - but I don't think it is being done.

With a bit of R and D it could be done in offset, however, there is no ROI for the vendor to do the work. There is no, or insufficient, customer (printshop) demand to develop such a solution. I know because I was involved in such a project in the late 90s.

Best gordo

There are so many lost opportunities.

Customers know what they want but they don't know what they need.

Suppliers provide what customers want and again not what they need.

Not much leadership in the industry. Too bad.

I would also add that the existing culture is what drives imaginative and innovative people out of the industry. People who were willing to take risks but in companies that were not.

 

[gordo]

Suppliers provide what customers want and again not what they need.

Not in my experience.
Suppliers typically provide what they can make money on rather than what customers want or need. Just one example...a native document creation application (inDesign, Quark, etc.) plug-in that would eliminate the need to do file preflighting at prepress killed because the ROI for the vendor was less than available from selling preflighting software.

best, gordo

 

[Deleted member 16349]

Not in my experience.
Suppliers typically provide what they can make money on rather than what customers want or need.

Just one example...a native document creation application (inDesign, Quark, etc.) plug-in that would eliminate the need to do file preflighting at prepress killed because the ROI for the vendor was less than available from selling preflighting software.

best, gordo

That is even worse.

I guess it is pretty common for suppliers to not want to undermine the revenue of their existing products but in the end, the companies that innovate and make even their own existing products obsolete, I hope would end up on top. Of course there is no guarantee of that happening.

The best defence against being sold expensive and poor performing technology is a well educated industry that demands better technology based on valid knowledge.

 

[gordo]

That is even worse.

I guess it is pretty common for suppliers to not want to undermine the revenue of their existing products but in the end, the companies that innovate and make even their own existing products obsolete, I hope would end up on top. Of course there is no guarantee of that happening.

The best defence against being sold expensive and poor performing technology is a well educated industry that demands better technology based on valid knowledge.

This thread has spun wildly off topic but it may be of interest, and related, to the OP.

In the case of the vendors that I've worked with (not just in the graphics arts) lead engineers may come up with a concept for a new product or service offering. They have to then present a research and data-based business case and plan to management. Management then reviews the proposal in the context of other proposals and makes the go-no go decision and releases the resources accordingly. Key to the decision are issues related to ROI, development timelines, competitive landscape, strategic value, etc, etc.

Then there's the customer and the incremental perceived value.

If customers are satisfied with the status quo, i.e. they don't see a problem with their current state of affairs then the solution may be a technical achievement and advancement from the engineer's or vendor's point of view - but it won't be purchased. And the product ends up in limited usage or dies.

Printers are, in general, not technical pioneers. Not marketing savvy (i.e. not really customer savvy). Not natural adopters of new methodologies. Don't really understand their business costs. And are secretive.

A tough crowd to convince to change no matter how intriguing a new approach or technology may be.

But you already knew that didn't you?

best, gordo

 

[Prepper]

Dot gain, TVI, Tone Curve, all depend on stable press

Dot gain, TVI, Tone Curve, all depend on stable press

"The problem is that in most shops there is a disconnect between prepress and pressroom."

Agree with that

"And press operators don't always understand how prepress can help them. So, if there is too much dot gain the press operator might lower SIDs to compensate, or switch to a higher tack ink instead of talking to prepress about how they can help bring things into alignment with plate curves."

In our situation, they do understand, and want us to adjust curves all the time to fix things for them, depending on how the press is running right then. Have not been able to get them to understand the connection between trying to keep the press aligned like it was the day the curves targets were printed, as much as possible, and having color "fall-in" and match the proof at startup, even though that is exactly what happens with new curves and the first runs with those curves. I believe they really think that color management
is something prepress uses to make the press print right. I've been trying to communicate to them that the pressroom has a part to play as well by keeping the press aligned as much as possible, all the while realizing that is the area of biggest variation and hardest to control. Still, whenever there's an issue, I have to prove first that the proof and plates are right, even though I have a "verified" proof off an Epson 7900 and an EFI Colorproof rip and thanks to you Gordo a plate curve verification scale.

"Dot gain is not the issue. The issue is tone reproduction."

I'm probably missing the point here but if dot gains vary on press, tone reproduction will vary also won't it? We're using curves to try and control dot gain either for a standard % or a tone reproduction curve. That's what I've been trying to pass on to pressroom here lately. Two things (for the most part) control color on press, density and size of the dot. Density is pretty easily controlled but dot gain is harder, IF dot gains can be kept as consistent as it's possible to do, from our experience here anyway, color can be managed so that when the press is started up with good plates and the right curves it will match a verified proof pretty close. If those dot gains change too much and the pressman is adjusting densities 20-30 points trying to match the proof then our solids are out of tolerance and at that point you can either try to re-align the press back to print similar conditions as the day the curves were made or make new curves and color will work again. Just can't get them to buy into that, enough to implement it anyway, so there is the disconnect again. Still getting the old, "color's not matching too good can you check the plates, or the proof, or adjust 5% out of the magenta for me?" when asked what are the dot gains today, "I don't know, they were okay last time I checked, I haven't changed anything out here." I'm very happy to have verified proofs and plates I keep checked up front to know where I stand going in. I wish I could convince them that putting the effort in up front, by keeping the press aligned, would to the same for them. Part of it is the old ways of just being used to having to custom adjust every job to try and make it work as well as possible.

Oh well...disconnect...no communication...whatever you want to call it, it keeps the print from being as good as it possibly could be. It makes people work harder to get lesser results.

 

[gordo]

"Dot gain is not the issue. The issue is tone reproduction."

I'm probably missing the point here but if dot gains vary on press, tone reproduction will vary also won't it? We're using curves to try and control dot gain either for a standard % or a tone reproduction curve. That's what I've been trying to pass on to pressroom here lately. Two things (for the most part) control color on press, density and size of the dot. Density is pretty easily controlled but dot gain is harder, IF dot gains can be kept as consistent as it's possible to do, from our experience here anyway, color can be managed so that when the press is started up with good plates and the right curves it will match a verified proof pretty close. If those dot gains change too much and the pressman is adjusting densities 20-30 points trying to match the proof then our solids are out of tolerance and at that point you can either try to re-align the press back to print similar conditions as the day the curves were made or make new curves and color will work again.

Dot gain (TVI) values are process monitoring metrics.

Tone reproduction curves represent the target for tone reproduction in presswork.

That being said, once you have established what dot gains are needed to deliver your desired tone reproduction then those dot gains become targets for which you establish tolerances which you may then measure for deviation.

The problem is that back in the day, and how probably most printers still operate, dot gains were written into print specifications (ISO, SWOP et. al.) as if dot gains were the targets.

The press operator's job is not to "make color" on press but to achieve and maintain the integrity of the ink film that the press is laying down. If the integrity of the ink film is achieved then (assuming prepress has done their job in proofing and plates) then the presswork will align closely to the proof. If the integrity of the ink film is maintained through the press run then color variation will be minimized.

Some adjustments away from target SIDs may be needed in some ink zones due to the mechanics of any given press as well as the ink usage across the live image area. That's OK. But on average, running to established SID targets during make ready should get the presswork in close alignment to the proof.

As a rule, press operators do not measure, nor need to measure, dot gain. Instead, dot gain (along with other metrics) can be used forensically to help understand why a particular press run failed to meet expectations.

Plate curves should not be used to compensate for press issues. Maybe just to get a specific job out the door but not as a fix for press issues. When a job fails, then it needs to be investigated and the reason for failure needs to be determined. If a shop is continually tweaking plate curves then they have a manufacturing process problem that needs to be corrected at the source.

best, gordo