Re: profiles and pantone colors
Re: profiles and pantone colors
- Subject: Re: profiles and pantone colors
- From: Marco Ugolini <email@hidden>
- Date: Sun, 01 May 2005 11:32:48 -0700
In a message dated Sun, 1 May 2005 10:21:09, Mark wrote:
> I actually had a press in mind when asking the question.
Any given press profile is able to match SOME of the colors in the Pantone
color library, as you well know, and which of those depends on the specific
space you are targeting (web coated, sheetfed coated, sheetfed uncoated,
Euroscale, Japan Color coated or uncoated, etc.).
Of course, using a 6-color process press (with Hexachrome inks, using a
modified CMYK set plus orange and green) allows one to match an even larger
percent of Pantone colors successfully.
Still, in any event, when using a press profile you are only managing the
process colors (be they 4 or 6). The spot colors still separate out to THEIR
OWN plates, so that the only real problem would be how to proof them, which
is what my reply tried to address.
> If I understand you correctly, a postscript file (or other file
> format) I generate from any of these programs will contain a
> specially named Pantone color that bypasses color management at the
> application or RIP level.
Yes. To be precise, the Pantone colors don't BYPASS color management: they
too are color managed, but in a different manner, i.e., through the use of a
named color library internal to the RIP which assigns to each color a
precise set of L*a*b coordinates.
> In other words, all these programs will understand that the colour I have
> defined, whether it's reproducible by the press (or inkjet) or not, is to be
> handled differently than the regular CMYK colors.
Yes. But not only differently: actually, completely SEPARATELY from the CMYK
space described in the target profile. And some will be reproduced
accurately while others will not, depending on whether they have a match
within the proofer's color space.
When handling Pantone colors, a RIP will completely bypass the target
profile and instead use the L*a*b values listed in its named color library,
then renders those to the source profile (the one that describes all the
colors in the inkjet device) based on an absolute colorimetric intent (and
perhaps using the white point of the target's profile: I'm not completely
sure about that).
> In the case of a press, I get a different plate for that Pantone and for an
> inkjet rip like those you mentioned, the special lookup table is used if my
> colour is defined correctly. If it's not, the pantone is just converted to
> CMYK and it may or may not be that good of a match to the actual Pantone.
It is crucial that the Pantone colors in a file be named correctly if they
are to be intercepted by the proofing RIP. But please remember that in the
case of a press, Pantone colors are ALWAYS still separated out to their own
plate(s), whether or not their colorimetric values are encompassed by the
press' CMYK color space. NO MATTER WHAT, the press profile is NOT meant to
be used to separate the Pantone colors to CMYK.
Usually these Pantone colors are OUTSIDE the color space of the CMYK press,
which is the common reason why they are used in the first place -- because
the press cannot produce them in 4-color process. But there are times when
even a color which the press COULD produce in 4-color process is defined as
a spot color anyway, and that is done so that this color can be maintained
stable, not dependent on the fluctuations in the CMYK plates (density,
pressure, etc.).
> Out of curiosity, what file formats can accept spot colours (either
> alone or in addition to CMYK)? Postscript, PDF, EPS, DCS?
TIFF for certain. And Illustrator (.ai) and Photoshop (.psd) for sure, too.
My knowledge of all this has a few holes, so I do stumble on the details. I
am not sure that EPS would work (though I think it does), or PDF (ditto).
DCS I have truly never tried. One other possible complication is the
rendering of spot color tints, which are a whole other can of worms.
Can anyone else help in defining the file formats that work in inkjet
proofer RIPs capable of matching Pantone colors?
Thank you, and best of luck.
--------------
Marco Ugolini
Mill Valley, CA
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