Disappearing dot gains?

[SteveSuffRIT]

I'm starting to get confused?
Are you saying that a 50% linear plate dot is measuring on the press sheet as a 47%, so -3%?
Again ISO would normally be about 16% (50% > 66%).
I assume your are measuring Murray-Davis (N=1, apparent with optical) and not Yule-Nielson (N>1, physical, mechanical).
Ignore the measured numbers for just a second, how does the image LOOK compared to your proof?
If what you say is true, the press should look lighter, weaker than the proof.

 

[gordo]

1) IS the CtP Imagesetter producing - Production Compliant - Imaging/Plate?
---> Yes. Tested and confirmed.

2) Surely there must be room somewhere for a PrintControl Strip.
---> On some jobs, yes, haven't had a chance to look at what's running to see what I can squeeze on, we're right in the middle of our big twice a year order and no one is letting me mess with anything right now.

3) What do you mean by Ryobi - only lets you put 1 Dot Gain Target?
---> Ryobi's closed-loop system will only work with Ryobi's supplied colorbar, yes, I could put other patches on that aren't read by the PDS, but again, not being allowed to mess with things right now.

4) Are you applying "Curves" to the PrintControl Strip - if so - why?
---> I'm not sure what you mean by this? I'm don't know what other RIP systems can do, but I don't get to pick and choose what part of a layout gets different calibrations applied to it. My only option is the whole layout gets processed with the same calibration curve to generate the plate TIF. Unless I double burn a plate with two different TIF's. But that's a whole different set of complications. If you're talking about linearizing the plates, then I do what I have always done, which is send over a linear 0-100 control strip, read that, and apply that adjustment to the plate profile. Then from there I run a control form and generate a characterization specifically for each press.

5) What happened a month ago in the Press Room for this problem to become apparent?
---> No offense, but if I knew THAT, I wouldn't be asking here. I have drilled through repeatedly with the pressmen to find out what they did, and they "claim" that they didn't change anything.

6) Has a "Print Test Forme" ever been used to test the Press?
---> Yes, regularly, whenever something drastic is changed. Like new rollers and such. As well as I try to run a G7 check and curve adjustment about every 6 months as the seasons change. I had not run one yet for this winter due to a lot of craziness going on in the shop, and now that we have this problem, I'm hesitant to run a reprofile until I have it figured out.

However, that being said, even with reprofiling, we're normally adjusted between -3% to +2% at 50% on my characterization curve. I have never had to go higher than that in all the adjustments. I am currently running at around 64% on all the colors.

I have heard (nudge nudge wink wink) that sometimes press operators dope their ink in an attempt to "fix" a press problem they're having. They typically keep this fact to themselves. Is it possible that you have a "Jack Daniels" on the press floor?
Could you post some micro photos of some 1/4 and 3/4 tone halftone dots? Preferably, for comparison, when the presswork was correct and now that it's gone wrong. And preferably in the live image area.

 

[Alith7]

I'm starting to get confused?
Are you saying that a 50% linear plate dot is measuring on the press sheet as a 47%, so -3%?
Again ISO would normally be about 16% (50% > 66%).
I assume your are measuring Murray-Davis (N=1, apparent with optical) and not Yule-Nielson (N>1, physical, mechanical).
Ignore the measured numbers for just a second, how does the image LOOK compared to your proof?
If what you say is true, the press should look lighter, weaker than the proof.

I'm not sure what there is to be confused about.
Profiling process:

1. Linearize plate to verify that when you send a 0-100 dot scale it's burning on the plate at 0-100, adjust slightly if necessary.
2. Send through a GATF layout at linear, set press densities to attain ideal LaB values at 100%.
3. Use those densities to run a few spaced sheets as close to "perfect" densities as possible.
4. Scan in IT8 forms into Colorpath Sync, analyze results & output a characterization set.
5. Update RIP with new curves, output a new set of plates, run to established target densities.
6. Scan in IT8, analyze, usually run another curve set.
7. Update RIP, etc.
8. Hopefully have a G7 passing press sheet (I usually manage it by the third set as long as the pressmen listen to me).
9. Repeat for round 3 adjustments if required.
10. This ends with a press profile that will pass G7 spec, and puts the 50% screen reading around 65-67% for CMY and around 70% for K.

When i'm talking about the -3% to+ 2% adjustment to the curve, i'm talking about the characterization curve applied to achieve G7 standard. Although I am sorry, the normal is a little wider range than that, but right now, I am pushed at 10% or a little more over my normal curves at 50%

 

[Alith7]

I have heard (nudge nudge wink wink) that sometimes press operators dope their ink in an attempt to "fix" a press problem they're having. They typically keep this fact to themselves. Is it possible that you have a "Jack Daniels" on the press floor?
Could you post some micro photos of some 1/4 and 3/4 tone halftone dots? Preferably, for comparison, when the presswork was correct and now that it's gone wrong. And preferably in the live image area.

Give me a minute to get the high-powered loop out and rigged up with my phone.

**** UPDATE for all ****
I pulled and reburned the TIF files from a run I did in June. So the ONLY thing that changed is from plate burner forward and it is MUCH lighter than my samples from June. SO, that settles the press / prepress issue.

Now we just have to try to figure out what happened. My plates do appear to be reading correctly before going on press, but just to be 100% on that, I'm going to burn a set on my other CTP (exact same machine and calibrated exactly the same so all files are interchangeable) just to verify for certain that that is not causing the problem.

Then it's time to start figuring out what the H#!! happened to the press.

 

[Alith7]

And now, for your head scratching, viewing pleasure:

I give you the reducing dot gain....

 

[gordo]

And now, for your head scratching, viewing pleasure:

View attachment 290526 View attachment 290527
View attachment 290528 View attachment 290529

I give you the reducing dot gain....

IMHO, there is no press problem. The dots are acceptably formed and don't appear to suffer from any ink/water issues. There appears to be a slight difference in SIDs but the problem is that the dots on the Old tifs/New run are physically smaller. I do not believe that a change in SIDs, press blankets, ink/water balance, impression cylinder pressure, etc. would account for this scale of difference.

This suggests to me that the dot gain compensation curves that are used are not the same. Either the plate linearization curve is no longer valid, so the subsequent curve is no longer delivering the same dots to the plates (e.g. the platesetter has been recalibrated (i.e. change in plate, change in processor, etc)) Or, the wrong curve is being applied, or swapped, in the RIP.

 

[Glenn McDowall]

Have a look at the dots with a microscope. Also find some fine text in a 100% colour. I've seen Ryobi press results where parts of the shape of the dot on the plate are missing or weak in the print, also it shows in a piece of fine text or solid stroke as gaps. I can't remember exactly what they did on the press to fix it but something about thoroughly cleaning the blanket or transfer roller. We struggled for about a week thinking our problem was plates, it was difficult with noisy dot shapes, but we could see it on a very small red object.

 

[Alith7]

IMHO, there is no press problem. The dots are acceptably formed and don't appear to suffer from any ink/water issues. There appears to be a slight difference in SIDs but the problem is that the dots on the Old tifs/New run are physically smaller. I do not believe that a change in SIDs, press blankets, ink/water balance, impression cylinder pressure, etc. would account for this scale of difference.

This suggests to me that the dot gain compensation curves that are used are not the same. Either the plate linearization curve is no longer valid, so the subsequent curve is no longer delivering the same dots to the plates (e.g. the platesetter has been recalibrated (i.e. change in plate, change in processor, etc)) Or, the wrong curve is being applied, or swapped, in the RIP.

The curves have been removed from the equation. These are the exact same 1-bit TIFS reburned. I did not reprocess the job through the RIP specifically to remove that from the equation. So where I am at right now is either (even though the plate reader says they’re ok) the plates aren’t burning correctly, or there is something with the press.

nothing to be be humble about Gordo, your experience is MUCH valued and appreciated.

On Monday we’re going to try to burn plates on the other plate burner for a comparison. To see if something is out of whack with the laser or something.

Now that we have removed prepress as the culprit without a question, I’m finally getting cooperation from the pressmen. Somewhat anyways.

 

[Alith7]

Have a look at the dots with a microscope. Also find some fine text in a 100% colour. I've seen Ryobi press results where parts of the shape of the dot on the plate are missing or weak in the print, also it shows in a piece of fine text or solid stroke as gaps. I can't remember exactly what they did on the press to fix it but something about thoroughly cleaning the blanket or transfer roller. We struggled for about a week thinking our problem was plates, it was difficult with noisy dot shapes, but we could see it on a very small red object.

I’ll add that to list of things to check next week. Thank you!

 

[SteveSuffRIT]

This ends with a press profile that will pass G7 spec, and puts the 50% screen reading around 65-67% for CMY and around 70% for K.

As I mentioned earlier, ISO expects linear 50% to gain 16% (50+16=66%)

 

[SteveSuffRIT]

The top row comparison photos look about the same to me!
Bottom row photos look different, but old run dots look emulsified.
So what's the story with the 2nd CtP? You never mentioned that before!
Do you have a way to track which plates are from which CtP?

 

[cementary]

Now that we have removed prepress as the culprit without a question, I’m finally getting cooperation from the pressmen. Somewhat anyways.

Ask them didn't they change plate-to-blanket pressures? If your press not running on bears it is possible for two situations:
1. Pressmen mount new pack under the plate with correct thickness and now dot gain is returned to norm
2. Pressmen adjust plate-to-blanket impression as part of regular maintenance

I remember plus 10% gain in 50% patch without doubling/slurring with excessive plate-to-blanket squeeze of about plus 0.1-0.15 mm over manufacturers recommendations. Slurring occurred only with lot's of ink on the plate, i.e. big 100% filled rectangles, with not all impositions

 

[cementary]

The top row comparison photos look about the same to me!

But they are not. If you scale them correctly, it's clear that cyan dots on previous run are bridged

 

[Alois Senefelder]

cementary,

I agree- but add that the New Run Cyan Dots also are bridged but to a lesser degree.

Alith, Please provide more micro pics of 1) Text 2) Slur Target and Star Targets and the Leave Edge of a Solid Area.

Regards, Alois

 

[SteveSuffRIT]

I reread this entire thread over again.
A sharpening of -15% on press is dramatic without any known changes!
Post #4 & #5 made me think I would take the larger size press plates, print them, then cut them down to fit on the smaller press and print those, with the same paper and density.
Thinking like a press operator, this is the only thing that would convince me the sharpening on press it's not a prepress issue (File, RIP, Curve, CtP, Plate).

 

[cementary]

I agree- but add that the New Run Cyan Dots also are bridged but to a lesser degree.

True, but add some optical gain with matte paper and here you are, 15 plus minus percent
I also agree that slur targets would really help here

 

[cementary]

this is the only thing that would convince me the sharpening on press it's not a prepress issue (File, RIP, Curve, CtP, Plate).

well, that really depends on the size of the dots. If topicstarter is talking about 100-150 lpi, i would agree with you. If 200 and more (FM/XM included) i wouldn't be so sure.

 

[Alois Senefelder]

Gentlemen,

We seem to be going round in circles! 1) we have a verified Imaged Plate - why aren't the Halftones being correctly reproduced on paper?

Regards, Alois

 

[gordo]

Some people may think differently about the necessity and/or practicality of including slur and star targets in a linear color bar, but IMO they are invaluable when visually checking a printed piece for properly packed cylinders, and print sharpness - especially the star targets.

A good point. If those targets are not available then any line art - eg text - will do since they are not affected by curves. If the line art is not thinner then it’s for sure a curve issue. If the line art is also thinner then that suggests a press or ctp issue rather than curves.

 

[SteveSuffRIT]

Side by Side comparison.