Re: [Gimp-developer] Interest for CMYK support

I am interested. I am new ti GIMP development, which I do in my spare time.
I am starting to modify the newsprint CMYK mode to directly separate into
CMYK layers instead of a flat image as it is now. The CMYK decompose
function appears to be broken in my version of 2.10, four black layers
appear. I will look into that also.

Cheers, and let me know what I can help with.


On Sat, May 18, 2019 at 9:28 PM Øyvind Kolås <pippin gimp org> wrote:

On Sat, May 18, 2019 at 10:33 PM Eleftheria Chatziargyriou via
gimp-developer-list <gimp-developer-list gnome org> wrote:
Hello everyone,

I am occasionally developing a colour theory library as a pet project and
oftentimes compare it against widely established tools. I was quite
surprised to see that GIMP doesn't offer any support for the CMYK mode.

I did a bit of searching around and it seems that the feature was popular
enough to warrant a plug-in (Separate+) which now seems deprecated.
that, I also found a few scattered threads requesting this feature most
which where redirected to the aforementioned plug-in.

Is there any interest for seeing CMYK support as a part of gimp, or is it
beyond the scope of the project?

It is very much in scope, and some of the internals are already ready.
The underlying core GIMP imaging libraries babl and GEGL provide
GIMP-2.10 with high-bit depth support. GEGL supports full internal
color management and mixing of image buffers in grayscale, RGB, CMYK,
CIE Lab color spaces of various bit depths and other aspects of pixel
format encoding. For tasks as image loading/saving from JPG/TIFF,
scaling, rotating, cropping, blurring, text-rendering, basic
compositing and more GEGL already handles CMYK.

Work is underway in GIMP's master branch completing refactorings that
add the previous big feature improvement of babl. The extension of the
pixelformat from keeping track of different encodings of possibly
unbounded sRGB based pixel formats to include color space information
as contained in RGB Matrix ICC profiles. That work which among GIMP
developers is known as the space invasion, since it adds better
support for color-spaces and it adds a space argument to many
functions also lays the foundation for later starting to add support
in GIMP for CMYK as a mode on par with RGB, Grayscale and Indexed.

Even after that is in place, for *photos* I would strongly urge to
work in RGB and use modern workflows with late-binding, totally
avoiding the new CMYK mode, there is other graphic design use-cases -
with vectors, text and more where it will be more useful; but not for
basic things like retouching and color and light adjustment in
photograhps. When constraints of other tools or workflow demands CMYK
TIFF or JPGs, conversion should happen at export time similar to what
separate+ provides, and the CMYK support would be limited to soft
proofing with the CMYK gamut.

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