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I am trying to make designs for printable products (shirts, mugs, phone cases, ...). I heard about the issue of the RGB and CMYK colors when printing. I am using Inkscape for my designs as it is a free, but it does not support CMYK colors.

I had an idea:

  1. Pick a CMYK color.
  2. Convert it to RGB.
  3. Working with this RGB color.
  4. When printed, the RGB color that came from CMYK will be converted back to the same original CMYK color.
  5. Then I get a color in print that is very close color to the original one, since CMYK color gamut is included in the RGB color gamut. So when I pick a color that can be found in the two gamuts in RGB, it will be the same when converted to CMYK.

Is this a good idea?

Or does anyone have alternative ideas on how to get similar colors when printing while the design is a PNG image with RGB colors ?

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    It may be cheaper in the long run to use software which actually support CMYK. A couple incorrect colors in a print piece, necessitating a rerun or causing a client loss, and the money spent (or lost) can quickly surpass the cost of a non-open source application.
    – Scott
    Jun 10, 2019 at 1:10
  • Will the printing actually be done with CMYK inks or would some spot colours be more useful? E.g., for printing a flag you might only use red, white, and blue inks.
    – Andrew Morton
    Jun 10, 2019 at 9:25
  • Not an answer in itself, but your question shows a fundamental but very frequent misunderstanding. An RGB triplet is not a specific color. Unless you couple it with a specific color space, you can't tell what any RGB triplet will denote. Consequently, you know nothing about whether the gamuts are compatible at all, much less anything such a broad statement that CYMK is included in the RGB. It isn't. There is no conversion between these color spaces in the sense you expect, all conversions are approximations based on specific (and hopefully not theoretical but measured) color spaces.
    – Gábor
    Jun 10, 2019 at 15:20
  • This means that a) you have to work in a color calibrated environment b) eliminate the need for unnecessary conversions. It is very common to design in sRGB (or any other specific RGB color space you have your environment calibrated for) and send it to the printing process later, so there is nothing wrong with that per se.
    – Gábor
    Jun 10, 2019 at 15:23
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    Digital printing often required RGB input.. But multiple color conversions also lead to multiple possible color shifts. It is always best to work in the color mode required for output. If output is RGB, then work in RGB. If output is CMYK, then work in CMYK -- at least for more accurate color rendering.
    – Scott
    Jun 12, 2019 at 23:38

4 Answers 4

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When printed, the RGB color that came from CMYK will be converted back to the same original CMYK color

Nop... It will not.

There are several reasons. Color profiles, changes in gamut, simulations on the screen...

But I will only address 1.

A CMYK value has 4 variables (C+M+Y+K). A given color can actually be created using a combination of inks, mainly what it is called chromatic and achromatic one.

When C+M+Y neutralize each other they produce gray, so this gray can be substituted with black ink at some percentage. Do you want to replace this gray completely with black? only half of it? 3/4, 1/4 1/10?

So there you go... You can have now, not only 2 ways of replacing one color but dozens of them.

The way you probably should go is taking one RGB chart. Here, have this one:

https://otake.com.mx/Color/RGB-01-Letter-LowRes.png

Import it on Scribus and take a look at how the colors are changed using some specific profiles... or If you can print the test chart on the same method you are going to use to print.

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  • maybe i didn't clarified well, but i actually doing what i said using Scribus and Inkscape, since Inkscape doesn't support CMYK colors i try different RGB colors in Inkscape that will not look different when i converting them to CMYK using Scribus, and as i read the CMYK colors that appears on my screen using Scribus will not be so much different when it is printed. but i can't find how to use different colors profiles in scribus when converting to CMYK , it just convert. maybe this is the wright way to ask my question clearly !
    – romaz2
    Jun 12, 2019 at 10:33
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You are not attacking the core issue of the problem.

It is perfectly fine to design printable material in RGB as long as you are cognizant of the fact that certain very vibrant colors wont come out as vibrant as you think and as a results crew up the entire palette. Just dont choose the most vibrant colors.

However, this is not a huge issue, you can learn to live with this. What you can not learn to live with is the lack of choice on how the black color is mixed. See RGB to CMYK is a one to many thing, each RGB value can be paired with any number of CMYK values. Even if you dont even care all that much what the colors are exactly the primary problem is that you have hard time matching blacks across assets.

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It's much more complicated than you think because CMYK is not CMYK and RGB is not RGB. But luckily, it most likely also isn't a problem. Be sure you have the correct color profile for your monitor so the colors that you see are actually the ones you expect (well, mostly... as good as you can get them), and you're almost certainly "good to go".

In respect to what something like CMYK means, there is a huge difference depending on what print technique is used (same goes for displays and RGB). Some print techniques have a surface on the color spectrum which is 5-6 times as large as others. They're still the same "CMYK". Some are wholly within RGB, some are not.

And then, RGB has half a dozen definitions as well which are all mostly overlapping triangles in the color chart, but well, mostly, not exactly. Your monitor is probably designed and configured to do sRGB. Which, compared to e.g. Adobe 1998 or Wide Gamut RGB is just puny. Some monitors display colors in 10 bit, some display them in 8 bits, and some accept 8 bits but really only display 6 bits. So you may not even be able to see what you do.

Converting CMKY to RGB means that maybe you cannot represent the color at all (physically impossible!), and vice versa. Thus, the idea of converting there and back between the two and getting predictable, always-reproducable results is flawed.

Is it a real problem?
Well it depends on your requirements. For most people (me included) it's a total non-issue. Unless you deliberately pick color values at or very near the border of the triangle, just do your work in RGB. Every non-junk printer will convert RGB to CMYK without you even knowing, do some more or less awesome color matching magic, whatever, and produce -- within its physical abilities -- a very usable result. For most people, that's just good enough.

CMYK is awesome at producing black, it's awesome at producing cyan, magenta, and yellow (well, duh!), and great at producing everything which is not too extreme red, green, or blue. It's not good at what remains, obviously.

Don't ask for something of which you already know beforehand that the printer cannot possibly deliver, and you're (usually) good to go.

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Modified:
The important thing here is the output. Just compare the results of on-screen colours and the colours printed. Are you satisfied with the results ? There are many other things you will need to keep in mind for achieving 100% same result. Just to add up, few things which matter:

i. Type of Printer (digital or offset) being used.
ii. Few ranges of RGB colors once converted to CMYK are not translated completely. Especially, the blues. Considered as most toughest colours to be be reproduced in CMYK (Tip: Avoid using blue). If you need more understanding, watch this: Why RGB Color Goes Flat After Converting to CMYK

I would like to contribute my opinion but before that its important to know:

- Are you using a digital printer or an offset printer?
- Have you tried to print something with RGB colors (for a while assume that you don't know about CMYK, and printing issue). If printed with this mindset, what was the result? How much different designed and printed colors were?

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