Dot Gain

[richie4400]

Hi There

Can someone please confirm my understanding of dot gain is correct.
We are currently printing to Fogra 45 standards which means a 40% CMY patch on the artwork should measure 56% (16% Dot Gain) on the printed sheet and a 80% CMY patch on the artwork should measure 91% (11% Dot Gain) on the printed sheet.

The reason I ask this is I had a visit from a "Colour Expert" and he said that a 40% patch on the artwork should print as 40% on the printed sheet. I see this as printing "linear" and not to any standard (ie Fogra).

Thanks in advance.

 

[Munsell]

That colour expert should have his badge taken away. You really don't want a press printing linear. Dot gain is normal and expected. You should work with it, not against it.

The way I approach it in our plant is as a process control tool. I don't shoot for any specific dot gain value. When I calibrate the press, I record the dot gain. As long as its something normal, I set that as the "standard". Then, it can be a tool to see if something is wrong with the press, or print quality. As long as I'm experiencing generally the same dot gain, I know certain aspects of the press are functioning properly.

 

[Lukas Engqvist]

Never trust an expert By CMY you mean a C, M or Y I hope. But you seem to be able to read the standard ok.

 

[richie4400]

Dot Gain

Thanks for your comments.

I agree you have to be careful when you put yourself out there as an "Expert"

 

[richie4400]

Sorry Lukas, I did not answer your question.
Yes, when I say CMY I refer to Cyan, Magenta and Yelo.

Many Thanks

 

[Lukas Engqvist]

Oh and make sure the sheet is dry when you measure dot gain, was too quick once and measured uncoated while it was still bleeding

 

[rich apollo]

Oh and make sure the sheet is dry when you measure dot gain, was too quick once and measured uncoated while it was still bleeding

Eek! That can be rough on the lens.

The "expert" in question is preaching against my experience. I set up a linear scenario like he describes...once. I learned that I like dot gain.

 

[JudP]

Hi All, so in regards to this dot gain question...I definitely agree with what Munsell says that this is a process control tool. I am currently implementing a major color management upgrade in my plant and as the Pressroom Manager I wanted to get some advice on what to do if my dot gain shifts. In doing my standardization runs, I do record my dot gain however this past week I've noticed that my dot gain on K, C and M have all decreased about 7% on my Goss Sunday 2000 (38" web).

Any advice on what to check for? I know the obvious, roller stripes, squeeze settings, etc but I can't think with anything that would cause such a drastic shift (or maybe this isn't so drastic????)

 

[gordo]

Hi All, so in regards to this dot gain question...I definitely agree with what Munsell says that this is a process control tool. I am currently implementing a major color management upgrade in my plant and as the Pressroom Manager I wanted to get some advice on what to do if my dot gain shifts. In doing my standardization runs, I do record my dot gain however this past week I've noticed that my dot gain on K, C and M have all decreased about 7% on my Goss Sunday 2000 (38" web).

Any advice on what to check for? I know the obvious, roller stripes, squeeze settings, etc but I can't think with anything that would cause such a drastic shift (or maybe this isn't so drastic????)

I'm not so sure that dot gain is a process control tool in the same way that it was in the days of film. Today, the dot gain characteristic curve is more of a target for tone reproduction in the press work. Because dot gain is tied to solid ink density, as SIDs naturally vary through the run, so will dot gains. There's a video on my blog that shows this quite clearly - click here: Quality In Print: On-press stability and consistency

Are you doing your standardization runs differently than how you run the press normally?

best, gordo

 

[JudP]

Thanks Gordo,

Much to my chagrin I only recently came across your site and have been reading all of your articles so well done on the good work and please, from all of us, keep it up.

I do see what your saying and this is what I thought too before I started researching this more and a lot of people say that they are now using this as a process control tool.

I want to start using this to target press runs to as well and will check out your video.

Our standardization runs are all done on the same stocks, same ink manufacturer, line screen, etc.

Jud

 

[rich apollo]

this past week I've noticed that my dot gain on K, C and M have all decreased about 7% on my Goss Sunday 2000 (38" web).

Any advice on what to check for? I know the obvious, roller stripes, squeeze settings, etc but I can't think with anything that would cause such a drastic shift (or maybe this isn't so drastic????)

Something that occurs to me, is that it is autumn. Have temperatures and humidity changed recently? They sure have here. Cooler temperatures (and lower humidity) will cause the ink to be more viscous - stiffer. That would cause lower dot gains.

 

[JudP]

Hi Rich, Well, I'm in Los Angeles and we unfortunately don't have an autumn...our facility is also fully climate controlled - temperature and humidity so I can't really blame the weather for the shifts that I'm seeing...

Best, Jud

 

[richie4400]

Dot Gain

Hi Gordo

I would value your opinion on my statement earlier in this post...

We are currently printing to Fogra 45 standards which means a 40% CMY patch on the artwork should measure 56% (16% Dot Gain) on the printed sheet and a 80% CMY patch on the artwork should measure 91% (11% Dot Gain) on the printed sheet.

The reason I ask this is I had a visit from a "Colour Expert" and he said that a 40% patch on the artwork should print as 40% on the printed sheet. I see this as printing "linear" and not to any standard (ie Fogra) and have you ever experienced anyone that prints to a linear state
or is my understanding of dot gain incorrect?

Many Thanks.

 

[gordo]

Hi Gordo

I would value your opinion on my statement earlier in this post...

We are currently printing to Fogra 45 standards which means a 40% CMY patch on the artwork should measure 56% (16% Dot Gain) on the printed sheet and a 80% CMY patch on the artwork should measure 91% (11% Dot Gain) on the printed sheet.

The reason I ask this is I had a visit from a "Colour Expert" and he said that a 40% patch on the artwork should print as 40% on the printed sheet. I see this as printing "linear" and not to any standard (ie Fogra) and have you ever experienced anyone that prints to a linear state
or is my understanding of dot gain incorrect?

Many Thanks.

I have never met a printer that prints a linear press sheet - i.e. 50% in the file measures 50% on the press sheet. To do so would make the presswork look low in contrast and washed out. You can certainly print that way if you choose to do so, however, you would be printing to your own shop standard rather than an industry standard.

According to the standard, Fogra 45 is for type 3 offset light weight coated papers using 150 lpi AM/XM screening.
The K is Curve C: 19% dot gain @40% (59% final tone) and 12.3% @80% (92.3% final tone)
The CMY is Curve B: 16% dot gain @ 40% (56% final tone) and 11.5% @80% (91.5% final tone)

However...

These dot gain curves named C and B are not contained in the ISO profiles or the Fogra published characterization data. Those files only hold D50 2° colorimetric data. The CMYK target print curves published by ISO are strictly valid ONLY for the ISO inks actually used by ISO for their test prints based on plates imaged in a linear film workflow. For a 40% Cyan the goal is not to match the ISO specified apparent dot gain, but the ISO specified 50% Cyan C.I.E. Lab D50 2° color, by using a different dot gain if necessary.

Now comes the confusing part....and the part that I don't fully understand....

Because these specifications are based on a linear film workflow, there are multiple dot gain curves represented in ISO 12647 which are presumably represented in the various ICC profiles derived from the characterization data that resulted in those press runs. It appears that, because the specifications state that "direct analogies to film production systems are maintained" the intent is to use these curves as the reproduction targets.
This means that there is no cross print condition standard and that some types of printing (20 micron FM curve F) cannot be done because the dot gains would be too high.
So the proofs for all these printing conditions would look different and so would the presswork.
To, me, the idea of having different tone reproduction curve targets for presswork for different processes or different halftone line screens is counterproductive to standardization.

best, gordo

PS I do not claim to be an expert. I'm always happy to be shown when I am wrong. Your color expert should have had a business discussion with you about presswork standards and why they should, or should not, be followed in your particular case.

 

[richie4400]

Hi Gordo

Thanks for your prompt response.
Your response is very informative and reassuring.

Thanks.

 

[rich apollo]

Hi Rich, Well, I'm in Los Angeles and we unfortunately don't have an autumn...our facility is also fully climate controlled - temperature and humidity so I can't really blame the weather for the shifts that I'm seeing...

Best, Jud

Okay. Have you confirmed that the plates are imaging correctly? I don't mean to be pedantic. I'm so apt to run off snipe hunting that I have to consciously make myself look at the obvious things first.

Is there any chance that the paper has changed? Is it coming from another mill? Has the pH changed? In a sheetfed environment, I would suggest changing the paper to see if the problem goes away. On a Sunday press that's not so easily done.

Do the dots look good on the paper?

 

[JudP]

Okay. Have you confirmed that the plates are imaging correctly? I don't mean to be pedantic. I'm so apt to run off snipe hunting that I have to consciously make myself look at the obvious things first.

Is there any chance that the paper has changed? Is it coming from another mill? Has the pH changed? In a sheetfed environment, I would suggest changing the paper to see if the problem goes away. On a Sunday press that's not so easily done.

Do the dots look good on the paper?

Hey Rich,

Did check the plates, this was the first thing that I checked. They are imaging correctly.

Same paper, same pH, came conductivity.

Now, here's what's driving me nuts:

Did a test run yesterday on Influence Gloss to check our plate curves. On the raw (no curves) run I had dot gain readings of:

k = 23.36 c = 24.99 m = 20.29 y = 25.03

SID: k = 1.60 c = 1.41 m = 1.34 y = .92

Did the verification run with the new plate curves and dot gains were:

k = 18.93 c = 13.03 m = 12.96 y = 15.15

SID: k = 1.61 c = 1.44 m = 1.33 y = .93

My solids were reading higher yet my gains were significantly lower!!

What is causing this?? The two runs were printed maybe an hour apart from each other.

Jud

 

[gordo]

Now, here's what's driving me nuts:

Did a test run yesterday on Influence Gloss to check our plate curves. On the raw (no curves) run I had dot gain readings of:

k = 23.36 c = 24.99 m = 20.29 y = 25.03

SID: k = 1.60 c = 1.41 m = 1.34 y = .92

Did the verification run with the new plate curves and dot gains were:

k = 18.93 c = 13.03 m = 12.96 y = 15.15

SID: k = 1.61 c = 1.44 m = 1.33 y = .93

My solids were reading higher yet my gains were significantly lower!!

What is causing this?? The two runs were printed maybe an hour apart from each other.

Jud

Caused by your new plate curves?

Your SID differences are insignificant.

Are you using terminology correctly? Dot gains are not targets. Tone reproduction curves are targets. I.e. you want a certain tone reproduction in your presswork, therefore whatever dot gain gives you that tone curve on press is the dot gain you want.

The steps are:
1) Define a target tone reproduction curve for your presswork.
2) image plates with no curve applied.
3) Run to your standard SIDS.
4) measure the dot areas
5) build compensation curves for the plate that will bring the presswork to your target
6) image plates with those curves
7) do a verification press run using those curved plates to confirm that the curves are correct.
8) adjust curves as needed

The assumption is that these press runs are dedicated - i.e. not tacked on to a live job.
best, gordo

 

[Alois Senefelder]

Variation !

Variation !

Hello JudP,

Paper is the remaining - Variable

May I suggest on the next print run -- you run sequential reels from, One Paper Machine Reel Position, try Centre Reels first then Centre Front 3 - Centre Back 4 e.g.
and see the print variation from One Paper Machine Reel.


Regards, Alois

PDFs "I hope you will find of interest and value"

 

[JudP]

Caused by your new plate curves?

Your SID differences are insignificant.

Are you using terminology correctly? Dot gains are not targets. Tone reproduction curves are targets. I.e. you want a certain tone reproduction in your presswork, therefore whatever dot gain gives you that tone curve on press is the dot gain you want.

The steps are:
1) Define a target tone reproduction curve for your presswork.
2) image plates with no curve applied.
3) Run to your standard SIDS.
4) measure the dot areas
5) build compensation curves for the plate that will bring the presswork to your target
6) image plates with those curves
7) do a verification press run using those curved plates to confirm that the curves are correct.
8) adjust curves as needed

The assumption is that these press runs are dedicated - i.e. not tacked on to a live job.
best, gordo

Hi Gordo,

Again, thanks for your input here.

I am sure that our dot gain differences are caused by our new plate curves. You're totally correct.

I do know that dot gains are not targets however my main question is what is the best handling when I do see shifts in our dot gains and how much of a shift is acceptable from run to run?

Best, Jud