Dan Margulis Applied Color Theory

Eurostandard and Custom CMYK

   Date: Fri, 26 Aug 2005 19:37:19 +0200
   From: Kim Müller
Subject: Custom Cmyk

I have been using Dan´s recommendation Custom cmyk with very good results. My standard settings for sheetfed ctp, coated stock: Ink Colors: Eurostandard (Coated), Black Gen: Light, Black Ink Limit: 85%, TIL: 325%, Dot Gain (50%): 62/62/60/66.

Now I separated a neutral rgb-grayscale with these settings, which gave a couple of points heavier yellow in the light end (27/15/17/0), but more magenta in the darker (85/72/67/55).

5% more magenta in areas that dark, and yellow being a weak ink, a couple of points more yellow in the lighter part. This might not have any practical significance(?) But anyway, -what is happening here?

Kim Müller
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   Date: Sat, 27 Aug 2005 02:18:47 -0000
   From: Stephen Marsh
Subject: Re: Custom Cmyk

Kim, simply that true 'LAB' measured neutral grey balance is not idealised, as is a human friendly system that may average things a bit, originating when scanning on a drum direct to CMYK and it was not common practise to select a LAB reading as it can be in Photoshop today.

So, the output profile for a particular print setting may specify grey balance for a light grey tone as 11c 6m 7y and this will read with zero AB LAB values.

A human operator, perhaps originally trained on a drum scanner or proprietary prepress system from before the desktop revolution, may specify grey balance for the same press conditions as 10c 7m 7y.

Evaluate the second CMYK numbers with the first profile and it will show that the tone is not neutral, as far as the profile is concerned...which supposedly reflects the press conditions.

Then in the real world of ink on paper, both may print an acceptable neutral.

Regards,

Stephen Marsh.
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   Date: Sat, 27 Aug 2005 12:21:55 -0400
   From: Dan Margulis
Subject: Re: Custom Cmyk Eurostandard

If you're happy with the current results then there is a case to be made for staying put.

I have had some experience with Eurostandard inks but I don't have samples readily available. However, the Custom CMYK defaults understate the potency of the magenta ink IMHO. I note that there is a difference of views among the computer-generated profiles: the new (uneditable) Photoshop Euroscale v.2 profile has the magenta 1 point higher than the yellow, but the Fogra Europe profile has it 6 points higher, similar to the Custom CMYK findings.

If this extra magenta is actually a mistake, it would manifest itself in darker skintones, which would be slightly too red. Also, darker pictures of natural greens, such as forests, might be a little muted. You should review some of your printed results to see if there is any hint of such a problem. If there isn't, you might wish to leave your profile alone. If you detect a small problem, or if you just feel more comfortable, you can always edit the ink values.

The way to do that in Custom CMYK is, starting with the Eurostandard Coated loaded, change the Ink Colors to Custom. That will bring up the ink color equivalents in xyY. Check the LAB coordinates box, and you'll observe that it asserts that an equal CMY mix makes a greenish yellow (-1.5a,6.5b). That would not be true with European or any other known inks. Also, it has the magenta ink tending toward blue rather than yellow.

If you would like to adjust these slightly, I'd add two points to both the A and B values in both the M and MY fields. For CMY I would insert values of +2a,+2b. Doing this will probably cut the magenta excess in the shadows by about half. I would not try to wipe it out completely as this might result in many pictures coming out too cold.

Dan Margulis
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   Date: Mon, 29 Aug 2005 18:15:03 +0200
   From: Kim Müller
Subject: Re: Custom Cmyk Eurostandard

I have had some experience with Eurostandard inks but I don't have
samples readily available. However, the Custom CMYK defaults
understate the potency of the magenta ink IMHO. I note that there is a
difference of views among the computer-generated profiles: the new
(uneditable) Photoshop Euroscale v.2 profile has the magenta 1 point
higher than the yellow, but the Fogra Europe profile has it 6 points
higher, similar to the Custom CMYK findings.

Interesting.

If this extra magenta is actually a mistake, it would manifest itself
in darker skintones, which would be slightly too red. Also, darker
pictures of natural greens, such as forests

The greens are quite bold, neutral grey a bit yellow, and there might be a little  bit too red in the shadow. My preference here is bold, strong  colors though. Anyway I will put some separation tests in the trim area when applicable.

equal CMY mix makes a greenish yellow (-1.5a,6.5b). That would not be
true with European or any other known inks. Also, it has the magenta
ink tending toward blue rather than yellow.

Very interesting. Anyone know the history behind why it was set up this way?

If you would like to adjust these slightly, I'd add two points to both
the A and B values in both the M and MY fields. For CMY I would insert
values of +2a,+2b. Doing this will probably cut the magenta excess in
the shadows by about half.

Meaning:
CMY  from -1.5a / 6.5b to +2a / +2b.
M from 67a / -5.4b to 69a / -3.4
MY from 59.3a / 40.7b to 61.3a / 42.7b

I would not try to wipe it out completely as this might result in many
pictures coming out too cold.

On a sunny exterior shot I have a preference for cold shadow. (Maybe it´s just a reflection of my nordic melancholia).

Thanks a lot.

Kim Müller