[scribus] mixing rgb and cmyk

Andrew A. Gill superluser at frontiernet.net
Tue Jun 24 19:18:37 CEST 2008

On Tue, 24 Jun 2008, Martin Tlustos wrote:

> I followed the thread about the real black in cmyk. Am I right in the
> conclusion that as far as possible it would be better not to mix rgb and cmyk
> in a publication, or does that depend on whether you mix images and graphics?
> Thanks for the explanation!

If it is at all possible, DO NOT MIX RGB AND CMYK.  It's not just 
white point.  There are a lot of issues that can come up with 
using the RGB color space for print media.  Some sRGB colors ar 
out of CMYK's gamut, and some of CMYK's colors are out of RGB's 
gamut.  Pure RGB black, as you can see, is not actually converted 
to 100% K, but 87/79/64/93 (which GIMP describes as having a hue 
of 219) and looks blue at higher values.

If you intend to print something out, always use CMYK.  Whatever 
software you are using will have to convert to CMYK anyways, 
because that is what the separations will have to be, and those 
are the colors of the inks that the printer/press will use, so 
starting CMYK can only help.  The advice for work that is 
displayed on a computer screen is to stick to RGB, since that is 
what screens use, but there are benefits to having that be CMYK, 
as well (for me, the addition of the K channel sort of acts as a 
separate value channel, which can be useful for brightening an 
image without introducing color shifts--I would love to see 
RGBW as a proposed standard).

There's also the possibility that it will mask some errors that 
won't be visible until press time.  For example, I went into GIMP 
and created a red image (255R/0G/0B), imported it into Scribus 
and created a red box.  Both are similar colors, and you might 
not notice any discrepancy until you get the plates back from the 
printer and for some reason, you've got both colors scaled back 
to a 90% linescreen, causing that nice, clean edge on the font to 
become ragged.

So CMYK for print work.  RGB for screen work.  But above all 
else, if ot's possible, do not mix.

| Andrew A. Gill     To ensure continued quality of service,   |
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Never mix, never worry.

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