[scribus] mixing rgb and cmyk

Craig Ringer craig at postnewspapers.com.au
Tue Jun 24 20:02:32 CEST 2008

Andrew A. Gill wrote:

> If you intend to print something out, always use CMYK.

This is not necessarily always the best choice:

- Many home printers expect RGB input and will do a very poor job when
   fed pre-converted CMYK data. You're better off using an RGB colour
   profile to transform colours for these printers, then let their
   drivers do the CMYK, CcMmYK, etc translation. This is especially
   important for "photo printers" and other six-or-more colour printers,
   as most CMYK spaces cannot represent their full gamut, where a
   wide-gamut RGB space like Adobe RGB is well suited to it.

- Modern print shops may accept PDF/X-3 with ICC-tagged RGB data. This
   lets you send your data to the print shop in their original colour
   spaces and lets their RIP do the conversion with its often superior
   knowledge of the performance of the press. Unfortunately, many
   print shops will just look at you funny and say "why do you want to
   send RGB?" because they just don't get ICC colour workflows, but
   a few are starting to get it. It doesn't help that ICC workflows are
   hard to get right and somewhat easy to misunderstand.

For most print shops, though, I agree that sticking to pre-converted 
CMYK is currently the way to go.

Craig Ringer

> 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.

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