RGB to CMYK with ISO web coated profile
by Andy Psarianos
In attempts to convert RGB data to CMYK using the ISO Web coated
profile I've noticed that the values of neutral areas appear to have a
lack of Yellow in comparison to the cyan and magenta separtions (at
least according to what I would expect).
Is there a reason for this that I am not aware of.
Are there any printers out there who have converted RGB to CMYK using
this profile who might be able to give some "in the trenches" points of
view on this somewhat "unconventional" grey balance.
kind Regards
Andy Psarianos
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19 years, 8 months
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Re: RGB to CMYK ISO web coated profile
by Jean-Marie Govaerts
Hi Andy,
You think there is a problem with the ISO web coated profile because the CMYK values of a neutral RGB values are not the same as we used to do it in a conventional way in the early days. Well, I think that is one of the wonders in color management.
It builds its profiles from the values of the measurement data. If there is less yellow in the CMYK gray balance (notice I do not say a lack off), it means that in the printing target the gray balance was a little to yellow. This does not mean there was a miss print. This problem is caused by trapping of the ink, and the sequence of the printing colors (KCMY or KMCY). Anyway yellow was probably printed last and so has the most effect on polluting the gray balance.
So if you use this profile, and it is printed in the same standard the profile will take care of the correct gray balance for your converted pictures.
Of course this also counts for the whole profile, not only for the neutrals.
Kind regards,
Jean-Marie Govaerts
19 years, 8 months
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RE: [ECI-EN] RGB to CMYK with ISO web coated profile
by Bestmann, Guenter RD-PN32
In the last years we had a lot of discussions about gray balance in the
german eci mailing list and I was involved in these discussions as the
"bad" guy, telling all people "forget the gray balance"!
Historically printing standards are defined in densities and gray
balance because of the measurement technology (only density and the
human eye). Color separations in scanners are done with defined gray
balances. The ISO 12647-2 gives some hints in the informative sections
for default gray balances if _not_ otherwise specified.
The gray balance depends on the inks used, depends on the colorimetric
values of the full tone color and depends on the printing sequence.
Because of this multiple dependencies gray balance is no longer (not
even an informative) part of the ISO 12647-2 (release this year).
In general it is possible to adjust the profiles (and characterization
data) to a defined gray balance. During proof you will not see any
differences because proof is a simulation of the gamut mapping (and
paper color) and all people will be happy with these profiles. But the
printer will be very disappointed, because if he adjusted the print
sheet for the correct full tone color and gets also the proper tone
value increase he will get an yellowish gray. To compensate for this he
has to adjust the full tone color to some values out of specification.
The ISO webcoated profile is a description of a real printing according
to ISO reference values. The printing conditions of the swop profile
differ from these conditions, therefore the gray balance values are also
different.
Regard,
Guenter Bestmann
-----Original Message-----
From: eci-en-admin(a)lists.transmedia.de
[mailto:eci-en-admin@lists.transmedia.de] On Behalf Of Peter Kleinheider
Sent: Wednesday, August 04, 2004 11:04 AM
To: eci-en(a)lists.transmedia.de
Subject: Re: [ECI-EN] RGB to CMYK with ISO web coated profile
Paul
This is just a recomendation and does not take in concern any color cast
of the paper.
the issue is: if a printer is printing according to ISO 12647, then the
colors will turn out to be gray on the prints (when doing a separation
of AdobeRGB or ECI-RGB to ISO Web coated)
Am 04.08.2004 um 10:55 schrieb Paul Sherfield:
> The grey balance for ISO for the CMY is:
>
> Cyan Magenta Yellow
> Quarter tone 25% 19% 19%
>
> Mid tone 50% 40% 40%
>
> Three qu. tone 75% 46% 46%
Peter
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