Xjyuk

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 dose 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 an alternative ideas to on how to get similar colors when printing while the designing is a PNG image with RGB colors ?

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.

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?

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. Abd a 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.