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Using Krita 2.9, Linux or Windows 8:

I open a flat RGB image in Krita and change its color space to CMYK using SWOP profile. Then I separate the image into its C, M, Y, and K components. At this point, I have 5 layers, including the original un-separated CMYK image.

I edit one of the layers. So far, so good.

Now, I wish to re-compose the image. Instead of separated layers, I want the image to be unified, in a way that incorporates the edits I made to one of the separated layers.

I cannot find how to re-compose the layers in Krita. Can this be done? It does not matter if I first delete the original layer, or not.

Note that the original image is not updated to reflect any change to a component layer. And, exporting to various formats (PDF, TIF, JPG) merely reduces everything to the topmost visible layer.

By comparison: The infamous separate+ plugin for GIMP will not only separate to CMYK layers, it will re-compose them with edits in effect.

EDIT: I discovered that GraphicsMagick can help me (outside of Krita). It can separate the CMYK image into its four channels as separate greyscale images. I can edit the separated images as greyscale, then re-assemble them to a single CMYK image, again using GraphicsMagick. The procedure is described on their website.

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  • I don't use the program but here is an idea. Can you paste each channel, in its respective channel in a CMYK file?
    – Rafael
    May 22, 2015 at 21:01
  • Yes. See my edit at the bottom of my original question. Taking the channels apart, then pasting them back together after edit, can be done by GraphicsMagick.
    – RobtA
    May 23, 2015 at 13:27

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At request of @gburning, I answer it myself:

Once I have the CMYK image, I finish it outside of Krita. I use GraphicsMagick (maybe ImageMagick would work too). The code is on the GraphicsMagick web site:

http://www.graphicsmagick.org/FAQ.html#how-can-i-extract-and-combine-cmyk-channels-in-a-cmyk-image

Works great. The reason I use it: I wish to ensure that a portion of the image (barcode), which should be pure black, really is pure K rather than rich black with some CMY. So I separate the image into 4 grayscale images that can be edited separately in any program, since they are free of color. Wash away any undesired CMY, then re-assemble to CMYK.

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I've found solution for your problem. You can recompose your image from separated channel layers. First you have to go to menu layer: Convert layer color space back to RGB from grayscale (to all three layers called red green blue) then go to layer properties and disable all channels except red for red, blue for blue etc. Last layer called blue you can leave then untouched. Now you can flatten your image. You can record your work to macro for future to speed up process.

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  • Unfortunately, that would defeat the purpose of what I am trying to do. That is, once I get it to CMYK, it will never see RGB again, so to speak. The solution outside of Krita, using GraphicsMagick, works best for me (see my edit to original post).
    – RobtA
    May 30, 2015 at 0:35
  • @RobtA You should add your edit as an answer so that it's easier for people who come across this question to see what your solution was.
    – gburning
    May 31, 2015 at 13:58

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