[scribus] Two color management questions

[Patrick Noffke]

On Thu, Jan 19, 2012 at 12:20 PM, Hadmut Danisch <hadmut at danisch.de> wrote:

> Hi,
>
> two newbie questions (using scribus for the first time for printing):
>
>
> I have to create a document with embedded pictures (digital camera,
> coming with embedded sRGB profile from Adobe Lightroom). The print
> service provider asks for PDF/X-3 and a Fogra27L profile.
>
>
> My two questions (scribus 1.4.0):
>
>  * Whatever I do, the PDF/X-3 generated by Scribus contains the
>    pictures still as RGB JPEG oder PPM. They are embedded with a PDF
>    reference to their color profile (sRGB), but I never found CMYK
>    images in the generated PDF.
>
>    The scribus manual says that it is the preferred way to leave
>    pictures in RGB and to have the conversion done by the printer's
>    RIP. This might be true for modern RIPs, but how could I make
>    scribus convert the embedded images into CMYK?
>
>
>
PDF/X-3 specifically allows the images to be saved in the file as RGB, as
long as they have a profile associated with them.  The profile(s) for RGB
images define what L*a*b* color you want for each RGB value for that image.

Then the output intent tells how to convert from L*a*b* to CMYK.  For
colors that are already CMYK, no further conversion is necessary (though
the output intent profile can be used to render how the image will look on
the printer).

Your printer has said Fogra27L should be your output intent.  Did they give
you an ICC profile?  Fogra27L only defines the L*a*b* color for any given
CMYK (also referred to as reference print characterization data in other
standards).  There are many options in going the other direction (from
L*a*b* to CMYK), and tools exist to create ICC profiles based on the
options you (or the printer?) choose.

Any printer that accepts PDF/X-3 should convert the RGB images to CMYK
(possibly during their RIP) using first the image profiles to convert to
L*a*b*, and next the output intent profile to convert to CMYK.  This should
be supported by their RIP software or some step in their process.  They may
add a further step that does ink optimization (i.e. GCR), which is supposed
to leave the color (L*a*b* value) alone.


>  * There are two different settings for the print profile.
>
>    One is under File->Document_Setup->Color_Management->Printer.
>
>    The other is under
>    File->Document_Setup->PDF_Export->Pre-Press->PDF/X-3 Output Intent
>
>
>    What is the difference between these settings? Both seem to describe
>    the printer the PDF is made for.
>
>
That confuses me, too.  Perhaps the first one is for rendering, but I'm not
sure.


>    And then, what's their meaning at all? If Scribus leaves the
>    embedded images as sRGB and depends on the printer's RIP to do the
>    conversion, what use do these settings have?
>
>
I hope this is answered above.  If it's still confusing, please let me know.

Pat
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