Dot Gain

[JudP]

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"

Alois - do you really think we would see dot gain differences between rolls of paper???

Our main paper is Influence Gloss and we only get it from one mill (Verso's Quinessec mill).

Thanks for the PDFs. You don't happen to have any TAPPI standards on tolerances for variations of paper color do you? I've been searching for these for months and can't even find it on TAPPI's web site.

Best, Jud

 

[gordo]

[SNIP]You don't happen to have any TAPPI standards on tolerances for variations of paper color do you? I've been searching for these for months and can't even find it on TAPPI's web site

Don't bother searching for that info - it doesn't exist.
The color of paper is identified using adjectives like "cream","natural", "white", etc. rather than objective definitions such as the CIEL*a*b* coordinates that printers use. Again, there are no specifications or tolerances provided by mills as to the consistency of a specific paper color either through the stack, roll, or when the same brand is supplied by mills located in different regions.

More info is here: Quality In Print: The paper problem

In my experience, the nice people that I've met at TAPPI conferences, where I've conducted seminars, know much about paper manufacturing but do not know very much about paper in the context of printing.

best, gordo

 

[gordo]

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?

You don't worry about it.

Question: How can you have a specification without a tolerance?
Answer: It's the printing industry.

There is no industry specification for dot gain and hence there is no specification for acceptable drift.

You could use the old SWOP wet proofing dot gain tolerances from the target values as a starting point:
Y: 15%-25%
M: 17%-27%
C: 17%-27%
K: 21%-31%
(as long as grey balance is maintained)

You have to define what is your tolerance standard, keeping in mind that dot gain is tied to SIDs and they are tied to image content among other things. This is something that you need to work out based on a knowledge of print production and application of basic statistical process control.

best gordo

 

[JudP]

You don't worry about it.

Question: How can you have a specification without a tolerance?
Answer: It's the printing industry.

There is no industry specification for dot gain and hence there is no specification for acceptable drift.

You could use the old SWOP wet proofing dot gain tolerances from the target values as a starting point:
Y: 15%-25%
M: 17%-27%
C: 17%-27%
K: 21%-31%
(as long as grey balance is maintained)

You have to define what is your tolerance standard, keeping in mind that dot gain is tied to SIDs and they are tied to image content among other things. This is something that you need to work out based on a knowledge of print production and application of basic statistical process control.

best gordo

Hey Gordo,

Thanks again for your input however something just occurred to me as I was thinking over your answer in regards to the gain differences that I posted yesterday.

The gain readings are being taken from the color bars and the on press CLC cameras. It therefore doesn't make sense that changing my curves would effect the gain readings yet if you look at the differences between the "raw" plates and the "curved" plates the gains are significantly different. The only thing changed were the plates - same paper (same exact roll even), same ink, same etch, etc.

Am I missing something here?

Secondly, I completely agree that we need to develop our own standards on gain based on our equipment, images, etc so my plan was once our plate curves are finalized and we have our standardization runs where we want them I would set these gains as my targets. Do you have the GRACoL or G7 standards/tolerances for gain?

Best, Jud

 

[gordo]

[SNIP]I completely agree that we need to develop our own standards on gain based on our equipment, images, etc so my plan was once our plate curves are finalized and we have our standardization runs where we want them I would set these gains as my targets. Do you have the GRACoL or G7 standards/tolerances for gain?

You don't appear to be understanding...as I wrote before: "There is no industry specification for dot gain and hence there is no specification for acceptable drift."
G7 is a grey balance method - no dot gain.
GRACoL 7 is a publication - no dot gain.

best, gordo

 

[rich apollo]

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

Is the plating curve being applied to the colorbar?

 

[richie4400]

Dot Gain

Hi Rich

dont know if this helps..

With regards to "industry specification for dot gain".
I print to Fogra standards, so the target TVIs that I aim for are available from the ICC website
link herewith: CMYK Characterization Data

I read my raw plates then create a curve to give these TVIs.

 

[JudP]

Is the plating curve being applied to the colorbar?

Hey Rich,

Thanks for the unintentional tip - yes! The curves are being applied to the color bar which explains by variations in dot gain from the "raw" run to the "verification" run.

Jud

 

[JudP]

You don't appear to be understanding...as I wrote before: "There is no industry specification for dot gain and hence there is no specification for acceptable drift."
G7 is a grey balance method - no dot gain.
GRACoL 7 is a publication - no dot gain.

best, gordo

Gordo,

Ok - I'm tracking now...took me a while but I do understand what you're saying on there being no industry specifications for dot gain.

So...in your opinion what do you think would be acceptable dot gain variation to see run to run and day to day on a brand new 6 color heatset web?

Jud

 

[gordo]

Gordo,

Ok - I'm tracking now...took me a while but I do understand what you're saying on there being no industry specifications for dot gain.

So...in your opinion what do you think would be acceptable dot gain variation to see run to run and day to day on a brand new 6 color heatset web?

Jud

In an earlier post I wrote:
"You could use the old SWOP wet proofing dot gain tolerances from the target values as a starting point:
Y: 15%-25%
M: 17%-27%
C: 17%-27%
K: 21%-31%
(as long as grey balance is maintained)

You have to define what is your tolerance standard, keeping in mind that dot gain is tied to SIDs and they are tied to image content among other things. This is something that you need to work out based on a knowledge of print production and application of basic statistical process control."

Basically though, in production printing you need to make sure that your plates are consistent. You don't worry or measure dot gain unless you have a problem aligning to the proof. I.e. you had no problem then suddenly you do. At that point dot gain may help you to figure out what has changed.

best gordo

 

[helmuttgutenberg]

Hi Gordo,

We have printed a test file and tried to cakibrate out Kodak Thermal CtP according to ISO 12647-2 for paper type 1 gloss and , printed the imeg with 60-70 and 80 lpc dots and looked at the ISO 12647 documents for TVI values, it says for 54- 70 lpc dot how about 80 lpcm dot any standarts?

 

[Lukas Engqvist]

I think the more practical approach is to deviate from ISO and ignore the lpc definitions. Customers will not want to have a different version of 50% grey at any LPI. The problem is that the ISO was defined as "this is what you get with a linear film".

Since most customer proofs, and separations will assume a FOGRA 39 on a type 1 paper your customers are most likeley to expect TVI value of 17 @ 50% for K (curve B) and 14% for CMY (Curve A) at any LPI. This is how the standard ought to have been defined if it is to gain status as "standard". As far as I know this is the defacto way of implementing it, even though "strictly speaking" it is breaking it.

For uncoated (type 3) the defacto curves are B for CMY and curve C (20 @ 50%) for K
For type 4 and 5 defacto curve C for CMY and curve D (22@ 50%) for K