Hi, "Joao S. O. Bueno" <gwidion@xxxxxxxxxx> 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. Sven
