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I am trying to print out a simple picture (below) that is composed of sections of the following RGB colors:

255,0,0

255,0,255

0,255,0

0,255,255

0,0,0

I am using this image for color sensing (with a sensor that measures intensity of red, green, and blue light) and need these values to be accurate.

The problem is, when I convert this image to CMYK for printing using an online tool, the equivalent RGB values are not accurate. I was wondering if there's any way to convert an image like this to CMYK for printing while maintaining the RGB values.

enter image description here

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  • Short answer: you can't print luminous colors using CMYK inks. That is why you can read a web page in the dark but you cannot read a book or magazine. – Jongware Jun 24 '18 at 20:43
  • Question shows a basic misunderstanding of the color systems -- just the idea of printing a color chart and expecting to pull RGB values from it. What is the context for expecting this kind of alchemy to be useful or even possible? – user8356 Jun 19 '19 at 17:19
  • Sorry... it's been a while since my formal education in coloring (way back in kindergarten)... my basic misunderstanding of the color systems has already been corrected by the kind and knowledgeable folks of this site, however. – Murey Tasroc Jun 19 '19 at 21:47
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You can't. It's not possible.

These colours are out of gamut for CMYK printing. As you can see below, the out of gamut warning symbols are circled in red. You'll need to choose RGB colours that are in the CMYK gamut instead.

enter image description here

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  • I don't understand why these wouldn't work: CMYK 0,100,100,0 for red... 100,0,100,0 for green... 100,0,0,0 for cyan... 0,100,0,0 for magenta... why wouldn't these perfectly represent those rgb values? – Murey Tasroc Jun 24 '18 at 22:43
  • Also it doesn't matter that it is exactly those values just that there are no other RGB channels in a given color (so for instance in 255,0,0 it could be 100,0,0 but not 100,20,15) – Murey Tasroc Jun 24 '18 at 22:44
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    @MureyTasroc You are right, on computer it should work and it really works. Your print service tries to be honest. There's no such CMYK inks that can produce pure screen colors on paper. – user287001 Jun 25 '18 at 1:02
  • @MureyTasroc - because these CMYK colours aren't the same as the RGB ones you have chosen. See here – Billy Kerr Jun 25 '18 at 8:04

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