Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.postscript > #234

Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black?

Show all headers | View raw

In article <208ecf3d-3629-4672-9a3e-
135e44701d6b@p13g2000yqh.googlegroups.com>, sd@imi.aau.dk says...

> I basically have the problem with print of some slides from
> OpenOffice. The problem is that OpenOffice exports the PDF of the
> slides as an RGB PDF, where the text color is R:0, G:0, B:0 - and
> usually when I send that to the printer, they complain that what
> should be plain black extends into all four (CMYK) channels, and so I
> have to pay more for the ink.

RGB->CMYK conversion often results in a mixture of CMY as well as black. 
OpenOffice being a disply-oriented application (like Micrsofot Office) 
probably only sets colours in RGB.

One thing you could try is printing to a PostScript file and converting 
that into PDF as a separate step. You haven't said which OS you are 
using, though I'm assuming some flavour of Linux. However its often the 
case that PostScript printer drivers understand about CMYK and will 
convert RGB into sensible colours.


> However, regardless of how they are reported, if I try to view their
> separations:
> 
> $ gs -sDEVICE=tiffsep -dNOPAUSE -dBATCH -dSAFER -dFirstPage=1 -
> dLastPage=1 -sOutputFile=p%08d.tif blah-slide-out.pdf && eog
> p00000001.tif
> 
> $ gs -sDEVICE=tiffsep -dNOPAUSE -dBATCH -dSAFER -dFirstPage=1 -
> dLastPage=1 -sOutputFile=p%08d.tif blah-slideP-out.pdf && eog
> p00000001.tif
> 
> ... I can still see that both of these PDFs still feature the text in
> rich black, in all four color separations.

You are still converting the RGB into CMYK, if the 
undercolorremoval/blackgeneration doesn't convert equal values of RGB 
into CMYK, then you get a CMY output. It doesn't really matter which PDF 
interpreter does this.


> So, I guess my questions can be summed up as:
> 
> * How can I convert a rich black text color in an RGB pdf - into a
> plain black text color in a CMYK pdf?

There are a number of things you could try, but I would suggest either 
printing to PostScript, and then using GS or sending the PDF file to 
Ghostscript. Because GS is a PostScript interpreter, there are things 
which can be done to colours.

It is possible to redefine the setcolor and setrgbcolor operators so 
that they convert equal amounts of RGB into a colour specification in 
DeviceGray instead (DeviceGray will convert to pure black in a CMYK 
workflow).

Its also possible to set up an under colour removal function which 
significantly affects how RGB is converted to CMYK (this is covered in 
the PostScript Language Reference Manual).


If you can post a (small!) example file, preferably a single page, to 
some publicly accessible URL I could take a look.



			Ken

Back to comp.lang.postscript | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? sdaau <sd@imi.aau.dk> - 2011-06-05 22:49 -0700
  Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? Matti Vuori <xmvuori@kolumbus.fi> - 2011-06-06 08:41 +0000
  Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? Helge Blischke <h.blischke@acm.org> - 2011-06-06 11:26 +0200
    Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? sdaau <sd@imi.aau.dk> - 2011-06-06 04:29 -0700
  Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ken <ken@spamcop.net> - 2011-06-06 14:05 +0100
    Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? sdaau <sd@imi.aau.dk> - 2011-06-06 08:34 -0700
      Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ken <ken@spamcop.net> - 2011-06-06 17:28 +0100
      Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ken <ken@spamcop.net> - 2011-06-07 10:21 +0100
        Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? sdaau <sd@imi.aau.dk> - 2011-06-09 05:28 -0700
          Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ken <ken@spamcop.net> - 2011-06-09 14:00 +0100
            Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? sdaau <sd@imi.aau.dk> - 2011-06-09 06:48 -0700
              Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ken <ken@spamcop.net> - 2011-06-09 16:06 +0100
          Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2011-09-16 18:33 -0400
    Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? sdaau <sd@imi.aau.dk> - 2011-06-06 09:17 -0700
      Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? Helge Blischke <h.blischke@acm.org> - 2011-06-06 19:30 +0200
        Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ole.hoppe@gmail.com - 2012-01-25 06:40 -0800
          Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? Helge Blischke <h.blischke@acm.org> - 2012-01-25 16:09 +0100
            Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ole.hoppe@gmail.com - 2012-01-26 06:41 -0800
              Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? Helge Blischke <h.blischke@acm.org> - 2012-01-26 21:07 +0100
              Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ole.hoppe@gmail.com - 2012-01-26 12:57 -0800
            Re: PDF to PDF (gs?): rich RGB black to plain K (CMYK) black? ole.hoppe@gmail.com - 2012-01-26 12:58 -0800

csiph-web