[filmscanners] Re: CMYK rant (was Digital Darkroom Computer Builders?)

["Anthony Atkielski" <anthony@atkielski.com>]

Andras writes:

> If, as Anthony said, CMYK is useful for printing
> work, then it only makes sense to use CMYK if you
> do it in the colour space of the printer AND convert
> to RGB using ICC colour profiles for display on
> screen.

If you plan to print the photographs, CMYK is useful.  It can even be useful
for printers driven in RGB, because the RGB gamut is larger than what any
printer can put on paper, and a conversion to CMYK can show you the limits
of the printed result on the screen (assuming that your CMYK conversion
parameters are _exactly right_, of course).  The reason you may not be
getting the vivid blue or rich green that you see on the screen when you
print on paper may simply be that it is outside the gamut of your printer.

> This is great, but it implies that the CMYK file
> is made for one and only one printer ...

Correct.  You always convert to CMYK with a specific printer and/or press
and/or inks in mind.  This is why you do most things in RGB (apart from the
fact that RGB has greater gamut and headroom), and convert to CMYK only when
you are producing an output file to go to the printer.

> ... so whenever a company buys a new printer
> that is different from the old ones in colour
> rendition, they have to discard (or adapt) their
> old CMYK files.

You don't keep CMYK files, anyway.  You recreate them from RGB for each use,
unless you are printing under exactly the same conditions each time.

> Also, more and more high-quality magazines etc.
> use more than 4 colours, in which case the
> entire method becomes useless.

Where did you hear that?  The vast majority of magazines and all other
continuous-tone printed matter is printed in four-color offset.  Six-color
is for special purposes and costs a lot more without necessarily adding a
lot more in quality.  The best four-color printing will look a lot better
than average six-color printing.

In any case, even if six-color printing were common, the process would still
be the same.  (I don't actually know if Photoshop handles six-color
conversions, though, as I've never had a need to prepare them.)

> My suggestion here is the obvious one -- why
> don't we all work in CIELab or XYZ and convert
> to RGB for on-screen display and CMYK for
> printing?

Mostly because of convenience.  Lab is fine for representing the gamut of
the real world, but no display or printing device can correctly render Lab
color, so there isn't much point in working in it extensively (although
Photoshop does use it internally).  The same is true for spaces like Wide
Gamut RGB.  Until and unless someone produces monitors, printers, or some
output device that can actually render the full gamut of Lab color, working
in Lab color will be of limited usefulness.

> Thus, I think CMYK is historical dead weight
> which has been obsolete at least since the ICC
> standard was created.

You're in for some unpleasant surprises the first time you become involved
in actually getting a photograph from camera to press sheet.  CMYK is
actually more important than it has ever been in the past, since so much
more is in color these days.  Even the cheapest newspapers are four-color
jobs today.

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