[Scribus] CMYK -> RGB strikes again

[David Purton]

On Mon, Feb 21, 2005 at 08:37:57AM +0100, Tino Schwarze wrote:
> Hi David,
> 
> On Mon, Feb 21, 2005 at 09:11:31AM +1030, David Purton wrote:
> 
> > > I've put up a web page describing my CMYK-RGB issues and illustrating
> > > them with pictures.
> > > 
> > > Anybody with hands-on CMYK experience, please have a look at
> > > 
> > >   http://www.tisc.de/cmyktest/
> > > 
> > > It all boils down to "how do I convert sRGB images to CMYK correctly?".
> > 
> > You can try using my patch for Scribus 1.2.1. (unless you already have)
> 
> I already patched my 1.2.2cvs (some two weeks old) with your patch - the
> files on the page were created with this version.

Really? I can't reproduce your behaviour.

This could be because there are yet more bugs in my patch ;) So let us
see if we can track down what is wrong:

Firstly, your initial conversion to CMYK. This looks exactly as expected.
(the bright green one). Remember when you look at this image in your
browser, gimp or image viewer, it is transformed back to RGB without
using profiles. You can confirm this by converting from the tiff to pdf
using tiff2pdf. Look at the resulting pdf in acroread and the colours
will look fine. Look at it in gv and they will look bright green.

Your proofs and out of gamut proof look as expected. I can reproduce
exactly. The out of gamut is ok, the nearest available match will be
used.



Now for your scribus stuff... This is going to seem like a dumb
question, but are you *sure* that my patch is applied? I ask, becuase
the output you get both for the PDF X/3 and the CMYK pdf looks like what
I get from an unpatched Scribus 1.2.1.

Have a look in scribus/util.cpp. If the patch is applied, the first
function you come to in this file will be be:

QImage LoadPict (QString fn, QString Prof, int rend, bool useEmbedded,
        bool useProf, int requestType, int gsRes)

If not, then either you have the first version of my patch without image
support or something went wrong and it wasn't correctly applied.

THe other possibility... Do you have an unpatched version also installed
on your system? just type "which scribus" in your terminal window to see
which one is being run.

Actually - I just thought of something. Turn on out of gamut checking in
Scribus. What colour is the out of gamut alarm colour? In my patch, I
changed it to bright green. Unpatched scribus uses grey. Also, unpatched
scribus will mark nearly all colours out of gamut, whereas my patch will
give the same results as displayed on your website.



This is what I get using your image and the ISOcoated profile you
recommended (PDF exported for printer (CMYK):

        http://marshwiggle.net/scribus/tino.pdf

Both the sRGB and the CMYK look nearly identical for me, both on screen
and in the CMYK pdf (When viewed in acroread 5.09, other pdf viewers are
not so good, of course)



Let me know how you go.


cheers

dc

-- 
David Purton
dcpurton at chariot.net.au
 
For the eyes of the LORD range throughout the earth to
strengthen those whose hearts are fully committed to him.
                                 2 Chronicles 16:9a
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