Denistometer V/S Spectrophotometer

[Deleted member 16349]

Studies have suggested that even an increase of .20 density (which would be beyond the standard range) would only increase the dot gain 2%. Dot gain is changed by roller pressure, water balance, viscosity, temperature, ph&conductivity, more so than SID

I went looking for some plots I had of Dot Gain vs Density that were done over 20 years ago, where I worked. 6 inks were tested. None were as low as 2% over 0.20 density points. Some were just over 6%.

Certainly the results of this kind of a test can be related to the strengths of inks used. Even in my plots, there were differences in the reference CMY group and the CMY trial group. The studies you have seen might have also used a non normal ink set.

But if one just practically thought about this. If it would be so hard to obtain dot gain changes with density changes, then why is it that historically discussions of dot gain also talk about adjusting density to get it into the dot gain range one would want. I think it would be hard to tell a press operator that adjusting his densities will not affect his dot gains much.

I have also been at a test were changes in water settings were done at the same density levels and I was surprised to see that the dot gain was not affected much. It was very strange because I expected they would and especially at these high levels of water settings where the plate was very shinny due to the water.

I suspect this might have been due to the type of inks used but I don't know. It was just a very interesting result.

Again, in my view, controlling the density level is the critical factor during a run for the consistency and predictability of the print. It is the foundation of offset and is a prerequisite before other issues can be fully resolved.

 

[gordo]

Ok, why then when the press gets a close match to the proof, it is also "gray balanced"?

Because both the proof and press were likely set up to an industry specification like ISO 12647 -X - and that specification is based on inks that under that press condition result in grey balance.

When it is color shifted away from gray, not the best matches. In that case, how do you suggest adjusting the color to match closer on a live job right then? Talking smaller tweaking moves here, not large moves, because large moves throw the solids off.

Correct. Small SID moves are always needed because of the mechanics of how a press "makes color." If you have to make SID moves large enough to push the press out of spec then something is wrong.

Are there presses that can be started up, ran to target densities and the color is right and doesn't have to be tweaked at all?

Theoretically a digital (inkjet) press. But not an offset press.

If it is being tweaked, it is towards something, more or less color, and gray balance is something that can be checked with a single measurement and provide info on leveling out the color, to meet the NPDC curves which are applied to the plate, which the profile is geared toward I assume (maybe not?), so it seems logical to me that moving to gray balance the sheet would improve the proof to sheet match, which is my only concern here. I really don't care how it gets there, if the proof I produce is a very close simulation of what the printed sheet looks like off the press, that is a success to me.

The press SIDs may be moved to better align with the proof and still be within tolerance while the grey balance patches are no longer grey. Putting the press sheet into grey balance does not necessarily mean that the press sheet has a better match to the proof. The proof is not a simulation of what the printed sheet looks like off the press. The proof is a target for the press to align to. That is a very important disti

G7 proof to me here means one that is verified "Ok" off my Epson 7900 and EFI rip to meet the Gracol conditions if that's a better term for you. Spec, standard, conditions, whatever you call it, G7 is the process we use here to print. That to me just means we're using the Gracol profile, proofing with that profile, NPDC curves, and when the press is gray balanced it matches really well and gets to color very quickly.

Probably don't use the "correct" terminology exactly but I do know the results we get are pretty good.

It is very important that the correct terminology is used in the correct manner otherwise confusion and misunderstanding will ensue. What would you think if you were in a car accident and you heard the doctors talking about your condition saying things like: "He's got a major owie in his leg and a boo-boo on his nose." "I think the owchie should be looked at first. How's his bum-bum.?"

G7 is a method for putting an output device into grey balance. Full stop. It does not refer to color. I.e. you can use G7 to grey balance two different devices but their color output can be very different.

You may have been set up to GRACoL 7 which uses the ISO 12647-1 specification (L*a*b* targets for paper, inks, etc. tone reproduction targets, etc.) for its print condition and used the G7 method to achieve grey balance.

best, gordo

 

[Prepper]

Because both the proof and press were likely set up to an industry specification like ISO 12647 -X - and that specification is based on inks that under that press condition result in grey balance.

Right. So adjusting SIDs during a run to maintain that gray balance will keep the press in the condition that matches that proof best.

The press SIDs may be moved to better align with the proof and still be within tolerance while the grey balance patches are no longer grey. Putting the press sheet into grey balance does not necessarily mean that the press sheet has a better match to the proof. The proof is not a simulation of what the printed sheet looks like off the press. The proof is a target for the press to align to. That is a very important disti

If a method is used that brings the press into gray balance across the entire tonal range while at the same time printing Lab solids that align (within tolerances) to the profile that method uses, then won't bringing it into gray balance better match the proof? Not just the gray balance of the proof but the solids also? If it isn't gray, then it's casted, to steal from Dan.

You may have been set up to GRACoL 7 which uses the ISO 12647-1 specification (L*a*b* targets for paper, inks, etc. tone reproduction targets, etc.) for its print condition and used the G7 method to achieve grey balance.

Ok, you're making a separate distinction here where I was lumping the whole thing together. Are they used separately? Do some use Gracol 7 but not G7? My understanding was that G7 stood for Gray and 7 solids, CMYK+CM+CY+MY. If so, the term G7 is not just referring to gray but the 7 solids and their L*a*b* color also isn't it?

Whatever process, method, standard you use, the main thing is consistency, if your print is consistent, your proof is correct, they will match as close as this process allows. The most important and hardest thing to control is TVI in my view. Solids are fairly easy to control but your blog showing the heartbeat of a single press run dramatically demonstrates TVI variation. We probably all make curves to either align dot gains to a specific tone curve with G7 or ISO specs, or whatever standard we're using (I know, I know, G7 isn't a standard), which are at best a snapshot of that press on that day and apparently during that hour.

That is the beauty of running to gray balance to me, making minor tweaks in SIDs to maintain gray from run to run, day to day, as the press changes and drifts up and down (heartbeat) keeps it printing that same general gray tone in neutral areas and within specified L*a*b* solids, and you can instantly see it visually in the gray bar if and when it gets casted, and measure it with one single measurement.

Color is made by the color\density\ink film thickness of the solid ink and the size of the dots, controlling the size of those dots is key but the hardest part, with what, 100+ variables that can and do affect it at all times? Amazing to me it works as well as it does...sometimes.

 

[danremaley]

Right. So adjusting SIDs during a run to maintain that gray balance will keep the press in the condition that matches that proof best.
Color is made by the color\density\ink film thickness of the solid ink and the size of the dots, controlling the size of those dots is key but the hardest part, with what, 100+ variables that can and do affect it at all times? Amazing to me it works as well as it does...sometimes.

Amen - and for more understanding go to <www.systembrunner.ch>

 

[rich apollo]

The press operator monitors and interprets press performance using the information provided by the color bar (and other image elements). Press operators know that presses are inconsistent but stable when it comes to laying down ink.

Absolutely untrue!

1) Press operators disregard colorbars in favor of playing grab-ass with the bindery girl. Then they wander off to the bathroom for a half hour. From there the press operators will amble back to the press console to consider how much beer is left in the cooler back home, and how much more will be needed for the weekend. After that, it's time for a smoke break.

2) Press operators know that presses are rock-solid, unchanging devices that never vary. They know that the earth is flat. They know that God lives in that mountain over there, and that he hates them.

 

[Alois Senefelder]

The Cure !

The Cure !

Hello Rich,


May I suggest you get them to "Kiss the binder's daughter" - no more wandering into the Bindery again.




Regards, Alois

 

[techkonusa]

I do not think it is a question of whether a densitometer or spectrodensitometer is the best instrument to be used for news print. As mentioned in an earlier post in this thread most densitometers that you purchase today are really spectrodensitometers because they have become affordable, are more accurate and offer several distinct advantages over that of a densitometer. But I will not get into all the advantages in this post.

Measuring all four process colors for each ink key and and adjusting the SID’s to be within acceptable tolerances and checking for excessive dot gain is the most commmon workflow. The 3 color gray bar is supposed to be neutral and not exhibit any type of hue shift. As we all know hue shifts in news print is fairly common. This is where a spectrodensitometer capable of measuring using the G7 method can enable you to fine tune the C-M-Y SID values and bring in your neutrals (50-40-40). They can provide ink key specific suggested density changes in your C-M-Y to hit your neutrals. A densitometer cannot do this. If you would like more information follow the below listed link. This is just my 2 cents.

A Functional Comparison of the Densitometer and Spectrophotometer

Bob Byrnes

 

[gordo]

Right. So adjusting SIDs during a run to maintain that gray balance will keep the press in the condition that matches that proof best.

Not necessarily. As I wrote before, the mechanics of making color on a proof are quite different than on a press. For (one) example, inline ink usage has no effect on an inkjet proof but it can have a significant effect on a press sheet.

If a method is used that brings the press into gray balance across the entire tonal range while at the same time printing Lab solids that align (within tolerances) to the profile that method uses, then won't bringing it into gray balance better match the proof? Not just the gray balance of the proof but the solids also? If it isn't gray, then it's casted, to steal from Dan.

On a test form yes. On live production jobs - not necessarily. If you look at press test forms you'll see how they've been laid out to try and compensate for how a press creates color vs a proofer.

Ok, you're making a separate distinction here where I was lumping the whole thing together. Are they used separately? Do some use Gracol 7 but not G7? My understanding was that G7 stood for Gray and 7 solids, CMYK+CM+CY+MY. If so, the term G7 is not just referring to gray but the 7 solids and their L*a*b* color also isn't it?

GRACoL 7 is based on/points to ISO 12647-1. G7 is a method for putting an output device into grey balance. Most graphic arts equipment vendors have tools to put output devices (proofers, presses) into grey balance. So, G7 is one method out of at least 5 others to do the same job.

Whatever process, method, standard you use, the main thing is consistency, if your print is consistent, your proof is correct, they will match as close as this process allows.

Yup.

The most important and hardest thing to control is TVI in my view. Solids are fairly easy to control but your blog showing the heartbeat of a single press run dramatically demonstrates TVI variation.

TVI is a measurement relationship between a solid color and a tone. As the solid changes so does the TVI - however, because they are linked it does not necessarily mean that the variation in TVI presents a problem.Unfortunately I no longer have the data to discuss this in any depth. It was a study that we did at Creo when we were testing FM screening. It's a topic that would be interesting for an independent research project.

We probably all make curves to either align dot gains to a specific tone curve with G7 or ISO specs, or whatever standard we're using (I know, I know, G7 isn't a standard), which are at best a snapshot of that press on that day and apparently during that hour.

Yup.

That is the beauty of running to gray balance to me, making minor tweaks in SIDs to maintain gray from run to run, day to day, as the press changes and drifts up and down (heartbeat) keeps it printing that same general gray tone in neutral areas and within specified L*a*b* solids, and you can instantly see it visually in the gray bar if and when it gets casted, and measure it with one single measurement.

Nope. I've done the studies and it doesn't work like that in real production.

Color is made by the color\density\ink film thickness of the solid ink and the size of the dots, controlling the size of those dots is key but the hardest part, with what, 100+ variables that can and do affect it at all times? Amazing to me it works as well as it does...sometimes.

Yup.

gordo

 

[gordo]

Absolutely untrue!

1) Press operators disregard colorbars in favor of playing grab-ass with the bindery girl. Then they wander off to the bathroom for a half hour. From there the press operators will amble back to the press console to consider how much beer is left in the cooler back home, and how much more will be needed for the weekend. After that, it's time for a smoke break.

2) Press operators know that presses are rock-solid, unchanging devices that never vary. They know that the earth is flat. They know that God lives in that mountain over there, and that he hates them.

Whatever was I thinking. You're absolutely right of course.

Mea culpa.

gordo

 

[nilay]

That was great discussion and sorry for late reply. I was out to Puerto Rico for vacation and joined back today. How about appling relative rather then absolute on densitometer?