Separate
CMYK Separation plugin for The GIMP
(c) 2003-2005 - Alastair M. Robinson <blackfive@fakenhamweb.co.uk>

Separate+
An improvement version of the Separate plug-in for The GIMP 2.2/2.4
Modified by Yoshinori Yamakawa <yam@yellowmagic.info>

Released under the terms of the GNU General Public Licence V2.
See the file "COPYING" for full details.

Version 0.5.2

Please note:
You use this software entirely at your own risk, I cannot be held responsible
for any damages caused by the use or misuse of this software.


Introduction:
~~~~~~~~~~~~~
One thing preventing The GIMP from being useful in a pre-press environment
is the lack of support for the CMYK colour-space.  This plug-in goes some
small way towards rectifying the situation, using a trick with layers to fake
CMYK support.


What can it do?
~~~~~~~~~~~~~~~
* Convert an RGB image to individual CMYK layers, using specified source and
  destination Colour Profiles.

* Save such a collection of layers as a CMYK TIFF.

* Proof the CMYK image on the monitor.

* Perform a "duotone" separation on an RGB image, reducing it to just those
  colours achievable with red and black ink.  (This feature does *not* use
  colour-profiles!)

* Load CMYK TIFFs into individual layers. 
  If you want to do that, please install "separate_import" plug-in.
  Then you can find the "Separated TIFF" item in the tool box's "File ->
  Acquire" menu.


What can't it do?
~~~~~~~~~~~~~~~~~
* Perform the "duotone" trick based on any colour other than red.


Requirements:
~~~~~~~~~~~~~
* The RGB -> CMYK conversion is performed with the truly excellent LittleCMS
  library (version 1.15 or later), so you'll need that installed.

* LibTIFF is also used, but since The GIMP itself uses it, its unlikely to be
  missing!

* ICC profiles.
  I recommend that you download Adobe's free colour profiles.


Installation (Linux):
~~~~~~~~~~~~~~~~~~~~~
If the GIMP 2.4.x is installed under /usr directory, type as follows:

$ unzip separate+-0.5.x.zip
$ cd separate+-0.5.x
$ make
$ sudo make install

Or, if the GIMP is installed under other directory(e.g. /opt), 
type as follows:

...
$ export PKG_CONFIG_PATH=/opt/lib/pkgconfig:$PKG_CONFIG_PATH
$ make PREFIX=/opt
$ sudo make PREFIX=/opt install

You can also install the plugin for a single user:

...
$ make INSTALLDIR=~/.gimp-2.4/plug-ins install-plugins

Separate+ serches the following directoreis for the colour profiles. If 
you want to use other directories, edit the line 483-497 of iccbutton.c
and recompile the plug-ins.

  /usr/share/color/icc/
  /usr/color/icc/
  ~/.color/icc/

To install the Adobe ICC profiles, you can get ZIPed profiles at the Adobe
web site:
  http://www.adobe.com/support/downloads/iccprofiles/iccprofiles_win.html

Finally, install the provided sRGB profile:

$ cp sRGB/sRGB\ Color\ Space\ Profile.icm /usr/share/color/icc/
  
The default profiles are:
  RGB: sRGB Color Space Profile.icm
  CMYK: USWebCoatedSWOP.icc


Installation (Windows):
~~~~~~~~~~~~~~~~~~~~~~~
Copy the plugins "separate.exe" and "separate_import.exe" to:
  %PROGRAMFILES%\gimp-2.0\lib\gimp\2.0\plug-ins\
or
  %USERPROFILE%\.gimp-2.x\plug-ins\

Also copy the "liblcms-1.dll" support library to:
  %PROGRAMFILES%\gimp-2.0\bin\
  
If you want to install the localized massage catalog, copy the .gmo file
into the correct folder and rename to "gimp20-separate.mo".

e.g.
> cd separate+-0.5.x\po
> copy ja.gmo "%PROGRAMFILES%\gimp-2.0\share\locale\ja\LC_MESSAGES\gimp20-separate.mo"

By default the plugin searches for colour profiles at:
  %SYSTEMROOT%\system32\spool\drivers\color\
  %PROGRAMFILES%\common files\adobe\color\profiles\

The default profiles are:
  RGB: sRGB Color Space Profile.icm
  CMYK: USWebCoatedSWOP.icc


Separating an image:
~~~~~~~~~~~~~~~~~~~~
To convert an RGB image to CMYK format, bring up the right-button menu, and go
to "Image->"  If the plugin in installed correctly, there will be a new menu,
"Separate".  From this new menu, select "Separate (normal)"; you will be
prompted to select an RGB source profile, and a CMYK destination profile.
If you have installed the Adobe and sRGB profiles as per the above
instructions, you can just accept the defaults for testing, otherwise you'll
have to locate the profiles manually.

A new image will be created with four greyscale layers, named "C", "M", "Y",
and "K".

If you have loads of memory to spare, you can use the "Separate (colour)"
option; this will perform the same operation, but the new image will contain
five layers: The first, "Background" will be white, and the other four will
be solid Cyan, Magenta, Yellow and Black, with the separated image data in
layer masks.  In addition, the layer modes for the four colours will be set
to "Darken Only". 
This gives a rough reconstruction of the colours, and is the next best thing
to a true CMYK painting mode, since you can paint on the layer masks, and see
the results in realtime.

This version of the plugin uses more realistic CMYK primary colour for the
CMYK simulation, which should greatly lessen the over-saturated look that
used to result.


Saving:
~~~~~~~
To save a CMYK TIFF for use in a DTP program, bring up the right-mouse-button
menu, and select "Image->Separate->Save...".  Please note that saving an image
this way won't clear the image's modified flag, so when closing, you'll be
warned that the image hasn't been saved.  This won't be fixed until the plugin
is capable of loading CMYK images. Until then, if you need to edit the CMYK
image in the future, you need to save it off in XCF format, to preserve the
layers.


Duotone:
~~~~~~~~
This is a little bonus, included simply because I needed it at work.
It reduces the colours in the image to those available just using red and
black ink, then creates a pseudo-CMYK image, with just Backgroud, K and M
layers.
The resulting image can be saved in the same way as a real CMYK image, but
the "red" data will occupy the "magenta" channel of the resulting TIFF.
