On Mon, Jun 30, 2008 at 1:55 AM, David Gowers wrote:
Hi John,
On Mon, Jun 30, 2008 at 7:22 AM, John Culleton wrote:
A book by MIchael J. Hammel, _The Artist's Guide to Gimp Effects_,
published in 2007, states that the "next release" of Gimp is
scheduled to offer the CMYK color model. But that seems not to have
occurred, alsthough there is a CMYK preview mode.
Is CMYK color model off the agenda for Gimp? It has been under
discussion for years. Other Open Source products, such as Krita
and Scribus, will work in that model. but they lack the capabilities
of Gimp. So is there any hope?
CMYK is definitely ON the agenda. It is a long term thing. GEGL is
currently being integrated. Once that is substantially completed (ie.
GIMP supports varying colordepths (8bit, 16bit, float,..) and
colorspaces (RGB, Yuv, LAB,..), working at an acceptable speed),
introducing CMYK support will be relatively simple.
I would expect that there might be some limited/experimental CMYK
support by 3.0, based on the current rate of integration.
Beware that in many instances people manipulating photographs in CMYK
mode in photoshop should probably have been working in RGB and
converting to CMYK in the end.
Currently GEGL is a powerful engine for processing in three
dimensionsal color spaces, most operations are performed in linear
light RGB by converting the pixels when needed (and avoiding to do
copies when possible). This works fine for RGB, R'G'B', CIE Lab,
Y'CbCr, HSV and other color spaces that are three dimensional /
tri-stimulus.
CMYK is not one of these as it is fourdimensional and a roundtrip CMYK
-> RGB -> CMYK isn't lossless no matter what precision your components
have.
The only way it is advisable to use GEGL with CMYK in it's current
state would only be for conversion to CMYK space as the final step. I
think this is sufficient for professional quality work for 98% or more
of potential users. The use cases involving actual processing or
compositing in a CMYK color model I'll say are outside the scope of
GEGL for now and would have be performed by processing the individual
color plates as grey scale layers. Even for pre-press this might be
enough since proper compositing in CMYK will probably involve knowing
how the ink spreads in the paper and physically interacts with the
light being reflected.
I am happy with GEGLs current limited focus on three-dimensional (plus
alpha) color models, this might be expanded with something resembling
spot colors, for z-buffers from 3d renders for use in compositing, as
well as native support for multi-spectral pixels if I find the need.
Native CMYK compositing and processing is something I consider to be
of little benefit to most and of minimal interest to myself, thus I am
unlikely to spend much time on it.
/Øyvind K.
