On Sat, May 18, 2019 at 10:33 PM Eleftheria Chatziargyriou via gimp-developer-list 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. Beyond that, I also found a few scattered threads requesting this feature most of 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.

/pippin - https://pippin.gimp.org/

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.

Octavio

On Sat, May 18, 2019 at 9:28 PM Øyvind Kolås wrote:

On Sat, May 18, 2019 at 10:33 PM Eleftheria Chatziargyriou via gimp-developer-list 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.

Beyond

that, I also found a few scattered threads requesting this feature most

of

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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