[Scribus] Re: Color issues in 1.1.0

[Peter Linnell]

On Fri, 2003-10-03 at 23:39, Sunil Joshi wrote:
> All:
> Elsewhere Martin had described some issues with colors of graphics in 
> 1.1.0 on Mac version of Scribus.  While that is indeed the case, I have 
> noticed a different problem.  I am noticing that when I export a 
> document as pdf, the colors are washed out.  Eg. here is a screen shot
> 
> http://www.suniljoshi.netfirms.com/scribus/picture2.jpg
> 
> of the print preview function of scribus on the left side, and the 
> acrobat file of the same page on the right side.  The brilliant greens 
> and yellows have been completely washed out in the pdf file on the 
> right side.  I wonder if any one else has seen this issue.
> 
> -Sunil
> 

This can be where you are using "printer" as a destination in exporting
a PDF and then judging on screen in Acrobat Reader. Using "printer" as a
destination will convert all RGB colors to CMYK upon export. 

Why? Acrobat Reader - even on Linux has does some color management
adjustments to PDF's which have CMYK colors, which is probably the case
here. 

The only time this is not true is if you have embedded or "tagged" the
PDF with ICC profiles. In this case Acrobat will honor the tag and
adjust accordingly, usually resulting in a much more accurate preview.

Both Franz and I have observed this with both Scribus files. I have
observed the same with PDF's which I have created in Indesign2 which I
fully enabled CMS throughout the process from PS6 and Illy > ID2 >
exported PDF. These PDF's are created on pro-level DTP gear which is
hardware profiled and calibrated - thus screen to print match with
correct settings is dead on. Yet, I still see the same "muting" of
colors in both Acrobat and Acrobat Reader.

The result is untagged CMYK will appear muted when viewed in Acro
Reader. GS View and other viewers will reconvert to RGB and give a false
impression. 

Note - this is important, the preview in Scribus is an RGB PNG generated
from raw postscript via Ghostscript. Now, I think the print previewer is
excellent, especially as it is derived from real postscript output and
no other DTP app has this, it cannot be trusted 100% for judging colors,
especially, judging from your screen caps, that you are pushing the edge
of CMYK gamut.

Now if you are viewing this in full Acrobat, it could be color
management is disabled or set with the wrong profiles.

Now that is the theory and mechanics of CMS...

Observations/Questions:

In your case, are you creating the colors in CMYK from the start ?

Have you created any kind of profile for your monitor using the
ColorSync wizard ? Without a color profile of any kind - all bets are
off for judging color based on the screen preview.

If these labels are intended for commercial printing, get the Adobe
profiles linked in the docs and use US SWOP on uncoated stock as a
starting point as your CMYK profile. That is a safe starting point.

If you intend to print these to an ink jet, keep your colors in sRGB and
export with "screen' as a destination. This is because most ink jet
printers although CMYK devices, the driver expects to see RGB colors and
will do its own internal conversion.

The kinds of deep blue and green highlights which are visible on screen
are often hard to reproduce with CMYK. This is called gamut compression,
where the dynamic range of RGB is higher than CMYK.

Welcome to the sometimes murky world of color management.

Now the other side of this is when Scribus has good profiles to work
with, the color matching is remarkably good. I created some PDF's of the
Scribus logo with lcms 1.11 and the screen to print is as close as I
would get from Indesign 2. So yes, the color management does work
properly.

Feel free to send me files for testing/comments.

Regards,
Peter