[scribus] Ink Coverage Preview differs from Acrobat Pro

[Patrick Noffke]

On Thu, Mar 7, 2013 at 10:32 PM, Jonathan Kreider <
jonathan.kreider at gmail.com> wrote:

>
> Does this mean that if I use the same profile in Scribus and in Acrobat
> that I should get similar results?
>
> It could be that I'm worrying needlessly about this.  It just seems to me
> that if I send the printer a pdf that needs less tweaking by their print
> system, then I will be more likely to have the results match my intentions.
>
>
Make sure you're creating a PDF/X-1a or PDF/X-3 file.  These are
"print-ready" files.  As Christoph mentioned, you should use a profile
recommended by the printer.  This should ideally match a color standard,
such as ISO 12647-2 or SWOP.

Note that there can be any number of profiles that "match" a color standard
(or a given printing condition).  These (print) profiles are used for two
primary purposes:  converting from L*a*b* to CMYK and converting from CMYK
to L*a*b*.  (You must associate other RGB <--> L*a*b* profiles with images,
which define how the images get converted to L*a*b*.)

For converting from CMYK to L*a*b*, this is fixed, and normally corresponds
to a standard printing condition.  That is, if a whole bunch of printers
claim they match ISO 12647-2 (for a particular paper grade), then if you
give them all the same CMYK separations, you should get the same L*a*b*
values.

For converting from L*a*b* to CMYK, this is where the variations come in.
 There are many (really, infinite) CMYK combinations that can produce a
single L*a*b* value.  So how you do the color separations depends on what
is embedded in the profile (which depends on the software used to make the
profile).  On top of this, GCR and ink (TAC) limiting can be embedded in
the profile, and there are lots of different ways of doing this.

By making a PDF/X-1a or PDF/X-3 file, you are specifying the "output
intent," which means you are associating a print profile that defines how
you expect the color to look.  In a perfect world, you have a profile that
perfectly matches what the printer is doing.  In reality, you get some
cases where the printer completely ignores the output intent.  The printer
may just assume you used some printing condition, and go with that.  If
they don't have a proof to go by, then you usually get something the press
operator thinks is right.

Unfortunately, the color standards have not kept up with the rest of the
print industry.  This is primarily because paper L*a*b* values in ISO
12647-2 are no longer available (I've heard this directly from a paper
manufacturer).  The standards do not currently allow for a method to
"correct" the output intent for a paper other than one in the standard.

I don't mean to crush your hopes.  I just live this stuff every day, and
I'm quite often hitting the limits of the standards.  But chances are, if
you use a profile that is close to the printing condition, you'll get a
good result (hopefully good enough).

Pat
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