[Scribus] slightly o/t: CMYK talk

Craig Ringer craig
Sat Oct 21 10:21:57 CEST 2006

stu seven wrote:
>    Also in this article, they say (sorry, I've lost the link) "using
> CMYK it is possible to exactly match on the user's computer
> what the printer will see"

That's basically impossible unless you have a printer or display device
with the same gamut and characteristics as the printer. The best you can
do is a good simulation with some attempt to correct for different
gamuts etc.

That's what ICC profiles are for, in essence. They try to translate the
characteristics of different output devices into a shared
device-independent colour space, so you can take a colour expressed on
one device and meaningfully relate it to a colour on another device.

The use of CMYK or RGB colour spaces has very little to do with this. As
Gregory accurately pointed out, the real point here is the use of a
monitor profile and a press profile to make a meaningful translation
between monitor and press colours possible.

It's still not exact, and never will be. There are colours your press
can print that your monitor simply cannot display. Tricks such as gamut
compression help with this at the cost of less accurate display of
colours that _are_ shared. Gamut warnings can flag those colours you can
not see (or colours your press can not produce that you have on your
screen). That's about the best anyone can to at the moment.

> - in other words, eliminate the problem
> of pictures which look one way on your computer, but prints
> differently.  This, I think, has always been the basic use and benefit
> of CMYK...

Not really. I suspect the author was writing from the perspective of a
user of QuarkXPress 4.x or similar, where the desktop publishing app its
self does not understand or support colour management. In this context,
what you do is you pre-correct your images in Photoshop with display and
printer profiles set up so the CMYK images output by Photoshop have the
ink values your particular press will require.

That workflow is largely (but far from completely) obsoleted when the
DTP application its self can handle the colour management internally.
You no longer need to work with CMYK images so long as your RGB images
have accurate profiles associated with them. If you do work with CMYK
images, you must make sure they fit your press specifications (ink
weight limits, etc) or they'll come out AWFUL.

What I'd recommend at this point is obtaining good colour profiles for
your printer, your monitor and any other devices (such as a digital
camera) that you use, and using that as a starting point. If you find
that you need finer control than that, then it's time to blow some cash
on a copy of Photoshop for your image work - and even then you'll
probably want to use those profile driven conversions as a starting
point for any tweaks and tuning you do.

Craig Ringer

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