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When I convert gray color swatch from RGB to CMYK InDesign transmit that as a mix of C, M, Y, K. How can I convert that values to K only?

The goal is to get clean gray colors on print output. Another question I have, is it beneficial to use 100% Black with adjusting the 'Tint' option instead (for getting gray)?

  • Use proper color library that is designed to translate RGB to K only. Or when exporting files use job that change RGB to Black. – SZCZERZO KŁY Oct 17 at 13:21
  • @SZCZERZOKŁY, in my experience it's not possible to automatically convert swatches in InDesign to grayscale. I would manually create the gray swatches. It would be interesting to see how it's done! About using 100% Black tints (instead of RGB gray swatches?). Well, yes if it's CMYK Black. If it's RGB Black it's the same problem. – Wolff Oct 17 at 15:48
  • @Wolff Yeah, I meant manually but with the use of dedicated library. It's been a long time since I allowed RGB gray swatched in my files. – SZCZERZO KŁY Oct 17 at 15:53
  • @SZCZERZOKŁY, by "library" do you mean "ICC profile"? And I do agree that it would be easier to just avoid RGB gray when neutral grays are wanted. You can have a mix of CMYK and RGB swatches if you want and only convert RGB to correct CMYK on export and leave the grays untouched (Preserve Numbers). – Wolff Oct 17 at 16:13
  • @Wolff ICC would be a part of JOB for pdf (but I learned it's better <than by profile> to do it semi-manual in Acrobat). I meant library in color mode. Which need to be done by hand (but only once). – SZCZERZO KŁY Oct 18 at 7:58
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You should set a profile that is set to change specific RGB range into K channel, otherwise you will the "dirty grey" when converting into CMYK.

If you are printing in office printers, many printer driver software allows you to create a custom profile. Turning off all the "vivid photo" options and setting the color management to "manual" would usually eliminate 75% of color problems.

On the other hand, if you are going to be sending it to a commercial printer, you should take into account that, 1. Printing machines add some paint in all channels; 2. Sometimes (as in very often) printers have their RIP set to add some paint in different plate to compensate for that.

So, to conclude, there is not direct way to maintain the grey value when converting from RGB to CMYK, due to the above mentioned factors.

Generally though, if you want to use grey, it would be wise to add it only in CMYK space.

  • The thing you say about "Printing machines add some paint in all channels" is only partly true. Digital printers, especially mid-low end, does this, but high-end digital print and offset print often preserves the chosen values. The RIP might lower the ink values to compensate for dot gain, but adding CMY ink to grays wouldn't be a nice thing to do as it ruins the work done by the designer. – Wolff Oct 17 at 16:18

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