ISO 20654

[Dario]

Generally speaking about printing spot inks screens...
How do you deal with it?
Do you use ISO 20654 somehow?
Do you press-proof every spot ink before running tha actual job?
A single TVI curve for everything?
What else?
...
Whatever to talk about is well accepted!

 

[SteveSuffRIT]

Do you think of ECG OGV as being like process or more like a Spot?
Instead of using Status T filters for density, for Spot I still use the custom narrow band filter at maximum absorption.

 

[Dario]

I'm talking about Measurement and calculation of spot colour tone value

 

[Ulrich]

I am working in a "normal" sheet-fed offset printing company with the usual portfolio: Posters, postcards, information- and self-presentation brochures, books (including art catalogs), and sometimes even packaging with subsequent individual finishing ...

I think that in order to obtain usable answers for you, you should know whether it is a matter of high-end control of high-quality periodically recurring packaging such as globally marketed cosmetics or "only" the "sporadic" use of special colors in existing CI's s or more or less experimentally creative use in graphic design or in duplexes or even triplexes ...

We do not work according to ISO20654.

In any case, we do not bother to record the spectral value of a 50% tone for estimated over 50 different spotcolors used per year and to recalibrate it via an extra curve in the RIP.
For "tricky" jobs, we sell a real print as an advance proof on edition paper in advance. Simply the cyan correction curve is stored for the exposure for FOGRA39 and 47 jobs. (because a color is mostly more near by Cyan or Magenta than black and black in FOGRA39 and 47 expect some more increase than C+M...)

Exceptions confirm the rule, there may well be a need to proceed differently elsewhere... but I think it makes sense to realize that spot colors have their original justification in the reproducible solid tone beyond color stability, color mixing and register problems to print, which can also be outside the usual CMYK color space.

Of course, tonal values can also be mapped / generated from it, or creative elements such as gradients can be used, but just because it is technically possible does not have to legitimize an enforceable "misuse" of the original concept ...: For everyday industrial production, it is already a challenge enough to use spotcolors to get the same full shade on different, even the same substrates ...

As I said, in the packaging industry there may be a need for more dedicated control here, but definitely not in this company, although i would say it is a quality-shop.

 

[Dario]

This is a nice testimony!
I also think it's too tricky to have a TVI curve for every ink - even if this is how I imagine how it should be.

 

[Ulrich]

... to have a TVI curve for every ink ... this is how I imagine how it should be.

As i meant above alredy: in cases of brand packaging control where every(!) parameter (really same ink mixture, substrate, lpi, etc...) is to control (and paid for the extra ...!) as a part of a special contract for such kind of job(s).

But normally there is much more Pantone in use than other spotcolors. Just think about the different editions of the printed fans and the determined - sometimes also different - Lab-values in the libraries (aren‘t they all measured and noticed with M2 on which paperwhitesubstrate?) and what you can get from different ink-suppliers...

Even Photoshop is not able to show you a Lab-Value of a spotcolor-tone in the info palette, so how do you want to control reliable a layout at screen as just a first step or a in digital proof if you can not be sure to get the solid that is predicted exactly...?

And then: For the run in the printing machine mostly the density must be varied so far as the result on that paper (which is for sure another than the original fans are printed on) is acceptable in a visual check against an original fan, what causes different and therefore not foreseeable real increases...

... but of course you can notice all that parameter for a second and third run, but i think the use for a really exactly screen proof is still limited... ;-)

 

[Dario]

Ulrich, I totally agree with you!
A workflow like this is impossible to me!
That's why I was asking fellows about their thoughts and procedures.

 

[SteveSuffRIT]

Tone Value (TV) or Dot Area of a Spot color can be measured and calculated from density.
Status T using Murray-Davies is for Process CMY but has too much noise for Spot.
But if you use a custom narrow band filter based on spectral curves maximum absorption, you get better results than Status T.

 

[Dario]

Tone Value (TV) or Dot Area of a Spot color can be measured and calculated from density.
Status T using Murray-Davies is for Process CMY but has too much noise for Spot.
But if you use a custom narrow band filter based on spectral curves maximum absorption, you get better results than Status T.

I'm not so tech-savvy for this ... I don't get it

 

[SteveSuffRIT]

Spectral reflectance is the raw measurement, it gets converted into density (D=-logR), which then gets converted into dot area or Tone Value (TV). Dot Area = 1-10^Dt-Dp/1-10^Ds-Dp, which is called Murray-Davies or MD.
Status T density is based Kodak Wratten filters that are 100 nm wide band. Red #25 for cyan ink, Green #58 for magenta ink, Blue #47 for yellow ink. Density works great for process inks (CMY) because the filters are opposite complements. R-c, G-c, B-y.
For spot colors, we create a "custom virtual" filter that is based on the lowest part of the spectral reflectance curve, which is the maximum absorption. It is a narrow band (1nm wavelength) so it produces maximum wanted signal with little unwanted noise. Dot Area calculation will uses same math formula or equation as before.
SCTV (Spot Color Tone Value, ISO 20654) uses XYZ Tristimulus values instead of density.