solid ink density adjust??

[mangcang]

Hey guys,

I cant understand why the offset press operator only measure & adjust process color solid ink density and how that can impact & make sure other tone values are correct. (For example, only adjust solid M density, how that affect 30% M, 35%M, 59%M...)

Or can I understand this way: If SID and grey balance are correct, other tone values will be correct.


Thanks a lot:-)

[gordo]

Hey guys,

I cant understand why the offset press operator only measure & adjust process color solid ink density and how that can impact & make sure other tone values are correct. (For example, only adjust solid M density, how that affect 30% M, 35%M, 59%M...)

Or can I understand this way: If SID and grey balance are correct, other tone values will be correct.


Thanks a lot:-)

You have to be careful not to mix up different metrics and what they mean.

The press operator measures SIDs because that is the only thing that he can adjust (plus water and pressure). SIDs are indirect measurements of ink film thickness which is important because that is what a press is designed to do - lay down a film of ink (well or poorly) onto a substrate. SIDs are also important for optimizing gamut (single color and over prints). Also, SID patches may be all that he has time to measure if he's using a handheld densitometer.
SIDs are not measurements of tone or color.

Because SID values are used in calculating dot gain, changing SIDs on press from the target will change measured tone value increase (dot gain) and dot area (tone reproduction). Changing SIDs from targets also impacts color.

In a production environment, if SIDs and grey balance are correct, other tone values may, or may not, be correct. Conversely, the press sheet can have poor grey balance according to the color bar but the color in the live image area can be correct. This results because of the mechanics of how an offset press lays down the films of ink.

From a press operator's point of view, the only targets in the color bar that are needed are the solid color patches (including overprints). He can get all the info he needs from those and the halftone dots in the live image area. The other color bar targets (grey balance, tone patches, slur/doubling etc.) are more useful forensically to try and understand what happened if there is a problem aligning presswork to proof.

Also, what call tones in presswork aren't really tones. Instead they are just areas of solid ink that happen to vary in size.

best, gordo

[mangcang]

Thanks gordo:-)

[Freeman A.Gain]

Well said Gordo!

[danremaley]

Hey guys,

I cant understand why the offset press operator only measure & adjust process color solid ink density and how that can impact & make sure other tone values are correct. (For example, only adjust solid M density, how that affect 30% M, 35%M, 59%M...)

Or can I understand this way: If SID and grey balance are correct, other tone values will be correct.


Thanks a lot:-)

Go to System Brunner AG for more information about measuring print. Felix Brunner says that 80% of color variance is caused by "dots", only 20% by "Solids". Therefore, if we only measure solids we're only checking 20% of the variance, sadly most pressmen only measure SID. GATF made the color bars for Komori which have 25,50,75% patches, as well as a 50% gray balance patch. All the other press manufactures from Europe, use 20-40-60%, based on their 'old' film (positive) based days. The plates need to be adjusted (Y-M-C-K) to produce gray balance on press at the require densities. Most printers have one plate curve, (or linear), for all colors - you need 4 separate curves.
I have a complete tone scale (wanted values) measured for uncoated paper, based on dot area, that produces gray balance at press. Simply print linear plates (of tone scales) at density, measure the dot area and adjust platemaker or film for the desired dot area, matched to the "wanted values" Works every time. It works for coated too, except not at the higher G7 densities. The 'secret' is that Photoshop conversions are based on 'gray balance' of C-M-Y, the same gray balance you are to achieve at press. (Did you know that RGB>CMYK conversions in Photoshop remove 20% weight for press gain?) If the gray balance is correct throughout the tone scale, then the associated colors will be correct as well, pictures are just tone scales that are mixed together. .. so. . that is why we need a color bar that has 25-5-75% patches to "read" the ever changing "dot area". Control of midtone dot gain / gray balance, is the single most important measurement on press. System Brunner, measures gray balance and opens or closes keys based on that measurement (NOT SID). It is the best color system in the world, with a built-in 5 star rating system. "Google Me" for more articles/information, hope this helps.
Call anytime 412.889.7643 Dan Remaley

[No.12 Looks Just Like You]

In my early days as a press helper, I brightly noted to the pressman "the marks aren't right".
He patiently explained, "we don't sell the marks"!!!

[mangcang]

thanks all the guys here~

[gordo]

The points you make have been discussed in depth in this forum - but I must respond because what you wrote is not completely accurate.

Go to System Brunner AG for more information about measuring print. Felix Brunner says that 80% of color variance is caused by "dots", only 20% by "Solids". Therefore, if we only measure solids we're only checking 20% of the variance, sadly most pressmen only measure SID.

1 - There was some truth to that in the days of film workflows - however that is not so true today with CtP and modern process control and QC systems. There is no dot gain adjustment on a press.
2 - There was also truth to that in the days of UCR separations. However, since the '90s pretty much all separations are GCR - there's not as much color in the CMY to vary.
3 - There is no useful connection between color shifts due to dot gain variation in the 3/C grey patches in the color bar and color shifts in the screen tint builds in the live image area.

GATF made the color bars for Komori which have 25,50,75% patches, as well as a 50% gray balance patch. All the other press manufactures from Europe, use 20-40-60%, based on their 'old' film (positive) based days. The plates need to be adjusted (Y-M-C-K) to produce gray balance on press at the require densities. Most printers have one plate curve, (or linear), for all colors - you need 4 separate curves.

Grey balance as a requirement to set up a press has been around for decades. And it was achieved using one curve for all plates. If you need 4 separate curves to achieve grey balance with today's equipment then you probably have a press condition that has problems that you should not try to fix with plate curves.

Simply print linear plates (of tone scales) at density, measure the dot area and adjust platemaker or film for the desired dot area, matched to the "wanted values"

In the vast majority of cases, making the plates linear to establish a baseline prior to building tone reproduction curves is redundant - a waste of time and can introduce another point of failure.

If the gray balance is correct throughout the tone scale, then the associated colors will be correct as well, pictures are just tone scales that are mixed together. .. so. . that is why we need a color bar that has 25-5-75% patches to "read" the ever changing "dot area".

That is simply not correct. But if it were correct - what would the press operator do to compensate for the "ever changing dot area"? That's right, adjust the SIDs.

Control of midtone dot gain / gray balance, is the single most important measurement on press. System Brunner, measures gray balance and opens or closes keys based on that measurement (NOT SID).

System Brunner measures the 3/C grey balance patches in the color bar. It does not use colorimetry it measures density. Here is a quote from System Brunner from "Using Colorimetry for Ink regulation? System Brunner replies to Heidelberg"
Quote: "densitometry is infinitely more important than colorimetry for offset printing, although colorimetry is indeed suitable for ink formulation, or logging runs with spot colors, or generating color profiles in prepress."

It is the best color system in the world, with a built-in 5 star rating system.

A key problem is that there is no specification or standard for what constitutes a "match" in printing for the live image area. Put another way, there are no specified tolerance in printing for the live image areas. Put yet another way, tolerances are a fundamental criteria for any activity called a manufacturing process. So, since it has no specified tolerances for its product, printing is by definition not a manufacturing process.
The System Brunner star rating system was IMHO a great attempt to quantify the correctness of the print run based on the ink densities measured in the color bar. Unfortunately it was not widely adopted.

best, gordo