Gray Balance

[tsdomenichelli]

Hello All,

I read a print book about gray balance and there have this information about gray balance:

- Heidelberg: 70% cyan 60% magenta 60% yellow

FOGRA: 28% cyan 21 % magenta 19 % yellow

Brunner: 50% cyan 41 % magenta 41 % yellow

Why this values?

I always thought that 50%C 50%M and 50%Y will generate the same of 50%B.

 

[meddington]

I always thought that 50%C 50%M and 50%Y will generate the same of 50%B.

Nope. Ink strength isn't linear. 50CMY renders a brownish tone in most processes at typical solid targets. Theoretically, its possible to render a neutral gray at those values, but solids targets would have to be adjusted, perhaps to a point to make other attributes deviant or unstable.

 

[TerryWyse]

Gray balance...it's all about relationships!

Gray balance...it's all about relationships!

The values you posted are all (more-or-less) in decent gray balance. "Gray balance" is not any one particular value but is more of a relationship between C, M and Y on a tonal scale or "gray scale step wedge". Typical values, give or take, used today for a neutral gray scale would be:

Highlight: 4c 3m 3y
1/4 tone: 25c 19m 19y
mid-tone: 50c 40m 40y
3/4 tone: 75c 66m 66y
Shadow: 100c 90m 90y (G7 would say 100, 100, 100)

So, you can see from this there's a RELATIONSHIP between C, M and Y where cyan is always higher than either M or Y and that M and Y are typically equal. It's important to note that these are *ideal* values but that, depending on the printing condition of a given press, the relationship or CMY values could be different than this to produce a true neutral gray. The values above are what you WANT them to be but it isn't necessarily so if the press is either not printing correctly or has not been "calibrated" correctly.

As far as 50c 50m 50y = gray, it's never been that way in the offset printing world but, in theory, there could be printing processes where 50/50/50 = gray....I just don't know of any!

You MIGHT be thinking of RGB as opposed to CMY(K) where, typically, equal RGB values WILL equal a neutral gray. This isn't ALWAYS the case but it's true of all the standard RGB working space profiles that are included with the Adobe applications.

Hope this helps,
Terry Wyse

 

[meddington]

Hey there Terry,

As far as 50c 50m 50y = gray, it's never been that way in the offset printing world but, in theory, there could be printing processes where 50/50/50 = gray....I just don't know of any!

Why not offset though? It is possible to alter the end densities so that 50c 50m 50y = gray, you just may be compromising other metrics, and hoping that the ink rheology allows it. You also would be printing outside of "standards". A very prominent G7 inventor (hint, hint) often makes the claim that this is possible, but perhaps too far from mainstream to be accepted. 50C, 40MY was chosen primarily as it was the amalgamated defacto of other print specs and best practices.

If you think about it, any time we deem that compensation curves or other correction factors are necessary to dial in gray balance for a printing system, we're essentially admitting that on this particular system, 50C, 40MY does *not* in fact equal neutral gray. So we alter those values (via curves or color management) just before imaging.

 

[Tarun Chopra]

It would be interesting to know historically from where and how did c25, m19, y19 / c50, m40, y40 / c75, m64, y64 values come into existence for greys? and why till date are we as an industry still following these values?

Thanks

 

[michaelejahn]

SWOP circa 1964

SWOP circa 1964

It would be interesting to know historically from where and how did c25, m19, y19 / c50, m40, y40 / c75, m64, y64 values come into existence for greys? and why till date are we as an industry still following these values?

SWOP - at least the 1964 version of SWOP - it was 50c 38m 38y - of course, this was on Champion Textweb, and with inks that no one probably makes anymore, and 133 line screen

Historically, they came from SWOP.

Consider the fact that following SWOP was mostly for people making film and sending them to magazines.

The entire idea of suggesting CMYK tint values to someone and expecting everyone to somehow print the same no matter what press, ink and paper is so (insert derogatory word here) I can't bare to think about it anymore, so I will refrain from posting on this thread anymore.

 

[meddington]

why till date are we as an industry still following these values?

Is there really a compelling reason to change, other than its easy to remember 50C, 50M, 50Y? Also consider that pushing densities to achieve neutral gray with those values significantly impacts overprint values and color gamut, nullifying the default separation settings for say, Photoshop. An individual printer could perhaps make these changes relatively easily with the tools available today, but in an industry that hardly turns on a dime and endlessly debates seemingly insignificant changes to current standards/specs, an enormous paradigm shift such as this could cause some to spontaneously combust.

 

[meddington]

The entire idea of suggesting CMYK tint values to someone and expecting everyone to somehow print the same no matter what press, ink and paper is so (insert derogatory word here) I can't bare to think about it anymore, so I will refrain from posting on this thread anymore.

I don't think this is necessarily the current industry suggestion at all, and would qualify your comment to say that suggesting CMYK tint values and expecting everyone to somehow print the same *without* compensating for the specific characteristics of the press/ink/paper attributes is (insert derogatory terms). It has become quite the norm to hand off common CMYK seps based on data such as GracolCoated1 or SWOP3, to any number of print processes using a wide variety of consumables, and I don't think its unreasonable to expect a similar visual result at all.

 

[gordo]

Is there really a compelling reason to change, other than its easy to remember 50C, 50M, 50Y?

50C, 50M, 50Y do not create (neutral) grey due to ink trapping issues and light filtering inefficiencies.
However, 50C, 50M, 50Y do create brown, and the notion of brown balance as the target for the press, rather than grey, has been around for quite a while. Unfortunately the print industry usually prefers to sanctify specifications before doing any research to establish the validity of the basis for those specifications. Basically the process is ready, fire, aim. Or more often, ready, fire.

Brown balance used to create colorimetric-based isometric tone reproduction to improve print standards has been the subject of several TAGA white papers and presentations (2004 & 2005) - most notably by William B. Birkett and Charles Spontelli of Doppelganger LLC who use brown balance in their print color consultancy.

Some issues related to grey balance as a metric for press production can be found here: Quality In Print: grey balance

BTW, I agree with Michael Jahn's concern since that it reflects exactly how the G7 method is promoted to the industry.

best, gordon p

 

[meddington]

50C, 50M, 50Y do not create (neutral) grey due to ink trapping issues and light filtering inefficiencies.

Well said. Not that its impossible to force neutrality from an 50CMY patch, but at the expense of other metrics.

Brown balance used to create colorimetric-based isometric tone reproduction to improve print standards has been the subject of several TAGA white papers and presentations (2004 & 2005) - most notably by William B. Birkett and Charles Spontelli of Doppelganger LLC who use brown balance in their print color consultancy.

I'm familiar with this work, and I can't say why it was not given more consideration as an industry accepted methodology, other than possibly due to the spontaneous combustion of those hearing it for the first time.

BTW, I agree with Michael Jahn's concern since that it reflects exactly how the G7 method is promoted to the industry.

I won't disagree that it has be inferred that G7 will improve visual match across devices and processes (perhaps beyond its capability) but not without compensatory methods. Further, the G7 How to, since its earliest version, has noted that G7 controls only the neutral gray scale. How well color will match would depend on the colorants in question and color management may be necessary to match a given data set. That said, its been my experience that simple 2D curves adjusting for gray balance often go a long way in improving visual match between two differing processes, as evidenced by the attached comparison of SWOP5 to Flexo on poly (ok, this is a numerical analysis, but likely more informative).

 

[Alois Senefelder]

Historical !!

Historical !!

Gentlemen, re Color Balance/Gray Balance may I suggest a name from the historical past, a forgotten pioneer

Louis Ducos du Hauron



Regards, Alois

 

[vaithi47]

50c 50m 50y dont make a grey because of the impurities of pigments in the inks.theoretically cyan on white paper absobs 100%of red light from incident white light.similarly magenta absorbs green and yellow the blue.so allthrre colours printed gives you black ie 0%reflection.but in practise the cyan is worst then magenta followed by yellow.this can be explained by measuring the hue errors with a densitometer.in an elaborate way you print 4 boxes cotaining 10 horizontal and 10 vertical squares each with a flat 10/25/50/75% tint of cyan and the horizontal boxes with yellow and the vertical sqares with magenta in tints 1to9/16to25/36 to45/62to71. with standard ink densities which you have established with cie l a b values.from each box you pick the neutral grey by measuring the lab values/the square which gives you equal densities thro all the filters as a netral grey is one withequal densities of cyan ,mag,yell and blk.this is the best method to establish the gray balance when you finger print your machine.this grey balance test is done after establishing your optimum densities and your tvi values