Dan Margulis Applied Color Theory
How to Edit Uneditable CMYKProfiles
How to edit uneditable CMYK profiles
Posted by: Dan Margulis
Date: Mon Jun 12, 2006 5:29 pm (PDT)
For some time there has been a lot of discussion here
about the inability to edit Adobe-supplied profiles, specifically SWOP v2,
in the cases when we need a different black generation. a different total
ink limit, or a different dot gain setting. Similarly, we cannot edit
profiles from third-party packages. As serious CMYK practioners require the
ability to edit these things, these profiles have always been of limited
use.
It turns out that there *is* a way to edit them, and if
somebody wants to write the proper Action with a nice pause in it, because
I'm on deadline, I'll be happy to include it in the forthcoming book.
To generate a SWOP v2 sep with, say, Heavy GCR, 80% max
K, 320% ink limit,
1) Start with two copies of the RGB file.
2) Convert to Profile 1st file using SWOP v2.
3) Convert to Profile 2nd file using Custom CMYK, 22%
dot gain (this is the closest match with default inks, you can do better by
editing them) and, Heavy GCR, 80% max K, 320% ink limit or whatever.
4) With both files now in CMYK, paste 2nd file on top
of 1st file.
5) Change layer mode to Luminosity.
Presumably for the sake of simplicity, Photoshop's
calculations treat CMY and black as separate items. Therefore, the black of
the merged document is pixel-for-pixel identical with the Custom CMYK
version, and the CMY component is recalculated to accommodate it. Doing
this effectively preserves the Custom CMYK total ink, too, although the
match is not exact.
IOW, if you have a screen grab that you desire to
separate using SWOP v2, you can do so and paste on top of it a Custom CMYK
version separated with Maximum GCR. The result is a file that matches SWOP
v2 closely for color but in which pure blacks separate to 0c0m0y100k, as
they should.
Dan Margulis