"Joao S. O. Bueno" <[EMAIL PROTECTED]> writes:

> > http://www.blackfiveservices.co.uk/separate.shtml

I am pointing people at this plug-in for quite a while already.

> I hacked together a plugin some time ago that uses the LCMS
> colour-management library to convert images from RGB to CMYK, using
> ICC profiles.
> Since the GIMP currently has no method of storing CMYK image data
> internally, I create a collection of layers, one for each channel,
> and use a custom save routine to create a CMYK TIFF from the layers.

I'd love to see the ability to convert to CMYK on save being added to
the standard tiff plug-in. A naive CMYK conversion function is now in
libgimpcolor but to make this really useful, the conversion should use
color profiles, so this should probably be done using lcms.

It should be goal for GIMP-2.2 to add a framework for handling color
profiles. Not only the TIFF plug-in would benefit from this. I know
that work is being done on a display filter for color proofing. For
this filter to be convenient and useful we will need a general way to
select color profiles and to attach them to images. And we will have
to improve the color display filter framework. This is working but
there's quite some room for improvement here.

At the moment our TIFF plug-in already reads ICC profiles and attaches
to the image using the "icc-profile" parasite (see
devel-docs/parasites.txt). If I remember correctly it also writes the
profile back to the TIFF file when saving. This parasite should be
used by other plug-ins as well.

The CMYK color selector we have is also a module and be exchanged by
an improved version that uses color profiles. So basically the
infrastructure is there that enables some basic CMYK support to be
added now without touching the GIMP core.

Someone or a group of people could try to come up with a CMYK
extension package for GIMP-2.0. I imagine this as a package that
contains a number of plug-ins replacing the standard file plug-ins for
CMYK-aware formats, a CMYK color selector module and a number of color
correction filters. If these plug-ins and modules all use lcms and
share ICC profiles by means of gimprc and parasites, you could use
GIMP to work on CMYK data even though it stores the data as RGB
internally. This is of course limited CMYK support only but it would
bring us a good way closer to it and I have been told that it should
be sufficient for a lot of tasks,

There are however one or two changes needed to the current module API.
Right now the modules have no way to access image parasites. Adding
this would probably be small hack only. If someone comes up with such
a patch quickly, perhaps we could even sneak it into 2.0 somehow.

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