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
