Introduction
Animenu
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Separate
EPIA TVOut driver
EPIA TVTool
XvTestcard
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A plugin providing
rudimentary
CMYK support for The GIMP
PLEASE NOTE: While my version of the plugin is still available
here, a much-improved version, maintained by Yoshinori Yamakawa, is
available at this address: http://cue.yellowmagic.info/softwares/separate.html
- you are strongly urged to use his version instead of mine!
DISCLAIMER:
As
with most of my projects,
this is
experimental software, and you use it entirely at your own risk...
Version
0.3
Many thanks to:
- Sven Neumann for doing much of the work involved in
cleaning up and porting the plugin to GIMP 2.0.
- Michael Schumacher for taking the time to do the Win32
build.
- Mat Caughron for
doing the MacOS X build.
Background
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.
The plugin is
unfinished, but usable for its primary purpose, and since
I'm
unlikely to have time to develop it further in the near future, I'm
releasing
it as is.
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.
- Optionally restrict separation of pure black pixels to the
black plate (useful for processing flattened PDFs with text).
- Perform a rudimentary background fill-in (Overprint) to
accompany the Preserve Pure Black option.
- Proof the CMYK image on the monitor. (This is
currently done as an Absolute Colorimetric transform from the CMYK data
back to the RGB profile; it should provide a pretty good side-by-side
match with a print.)
- 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!)
What can't it do?
- Load CMYK TIFFs into individual layers. If you want
to edit
a CMYK image, save it in XCF format as well as CMYK TIFF, so the layers
are
preserved for future editing.
- Embed ICC profiles in the generated TIFF.
- Perform the "duotone" trick based on any colour other than
red.
Requirements:
- The RGB -> CMYK conversion is performed with the truly
excellent
littlecms library, so you'll need that installed. (The win32
version
includes a pre-built dll, and for GPL-compliance, the source too...)
- 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. A Google search for "Adobe ICC Profiles" will
find
them...
Installation:
Installation
instructions for each platform are
included in the archives.
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
instructions in the archive, 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.
*NEW for 0.3* -
the "primary" colours chosen for the "Separate
(colour)" mode are now much more akin to the primaries used in
printing, which are nowhere near as bright, saturated and downright
lurid as pure screen Cyan and Magenta! This gives a far more
realistic preview of the colours.
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 Background, 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.
Download:
Linux
(source + binary) for GIMP 2.x
MacOS X
(source + binary) for GIMP 2.x
Windows
(source + binary) for GIMP 2.x
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