I do not know when support for CMYK in GEGL will be added, but the
initial support will most probably be as described below,
and it can be added without being intrusive on the current code.
The various tasks that needs to be done should probably be filed
against GEGL as separate enhancement requests in bugzilla.
GEGL itself at the moment focuses mostly at mixing and processing High
Dynamic Range additive RGB light. When introducing CMYK subtractive
mixing will be added but initially only for export purposes. The
following new operations would be desirable:
It should be possible to transform buffer data to CMYK buffers by
supplying an ouput profile and a rendering intent, as well as
rendering a mask indicating out-of-gamut colors. Both of these tasks
will be implemented as operations. And should provide a core set of
functionality allowing some control over generated CMYK values, and
for most uses sufficient control.
These operations will need some changes and additions to the GEGL code
most specifically a ICC profile property on GeglBuffers that is
propagated correctly through the graph.
When matching colors in a print job between rasters originating mainly
in photographs with CMYK vector graphics, it would be advised to use a
color picker on the written output CMYK file intended for inclusion in
print. Since if
painting is done on RGB buffers in this model with colors picked in
CMYK, the information about the black seperation in the user specified
CMYK values is lost.
It should then be possible to add CMYK specific operations, as well as making
the existing internal ones CMYK aware. For some operations where
abstracting away the number of colorant components, it might be
desired, but in most instances I would argue that it adds unneeded
complexity to the code.
Being able to preview the range available, perhaps even using
perceptual compression of values for display.
The operations could perhaps be structured as follows:
apply-profile
-------------
apples a color profile to a buffer, should be followed by an operation that
expects CMYK data if the buffer has been converted to CMYK in the
process to avoid information loss.
properties:
profile - ICC-profile
intent - absolute colorimetric, relative colorimetric, perceptual.
convert - boolean value, convert image default value is TRUE.
gamut-distance
--------------
generate a gray scale map indicating how far outside the gamut
boundary a color is.
properties:
profile - ICC-profile being converted to.
A sample chain of operations taking a photo from a raw file, and
making a sharpened CMYK file tagged with a profile.
load
path:rgb.raw
apply-profile
profile:mycamera.icc
convert:false
apply-profile
profile:sRGB
convert:true
auto-levels
unsharp-mask
std-dev:3.0
amount:0.2
apply-profile
profile:swop.icc
convert:true
save
path:cmyk.tiff
/Øyvind K.
--
«The future is already here. It's just not very evenly distributed»
-- William Gibson
http://pippin.gimp.org/ http://ffii.org/
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