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I see some professional printers asking for documents using CMYK instead of RGB. But I don't understand how it is better than RGB with an appropriate ICC color profile. Indeed, if my understanding is correct, the ICC color profile of the picture matches a RGB coordinate to an absolute color representation in XYZ or CieLab, and the ICC profile of the printer should allow to convert an absolute XYZ to the printer-dependent CMYK color.

So why does it matter if we start from RGB or CMYK since anyway we need to convert the color to XYZ before printing?

And from my understanding, most rgb color profile gammut are bigger than what a printer can print anyway.

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    CMYK is predominantly used for making separations for offset lithography or screen printing - for making plates, and screens. It's not generally required for digital printing. It really depends on the type of printing being done.
    – Billy Kerr
    Mar 2 at 17:36
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    @tobiasBora as you have very good answers, just a comment: if you have good relations with a specific shop, you know their system, expertise and workflow and you're sure you can rely on it, you might want to give them RGB, yes. Without that, you're still much safer to give them CMYK that's created according to your specific needs. Provided you already learned the whole rigmarole because color management is no small endeavor. :-)
    – Gábor
    Mar 3 at 17:28

2 Answers 2

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I see some professional printers asking for documents using CMYK instead of RGB. But I don't understand how it is better than RGB with an appropriate ICC color profile.

This is actually a good question. In my opinion, the answer is beyond color, it is beyond print. The answer is responsibility.

One example. Almost every photo in its digital form starts as an RGB image. Of course, at some point to be printed will end as CMYK values. It could be inside the printer software just before printing.

But you used the important words: some professional printers not every printer, some. So the answer is:

In some cases, when you are printing a specific project professionally, you need to be responsible for the CMYK values you need.

In general, the process is pretty obvious as you mentioned.

You take your image with an RGB and apply a conversion using a specific CMYK profile. You as a professional in the graphics arts are choosing the conversion, and then the values are fixed for that project... But...

This also means there are different ways to convert the image...

  • You could have a different TAC value
  • you could need an overprint
  • you could need a different rich black
  • you could need an achromatic print
  • you could need to reduce the risk of misalignment of the plates
  • you need to match some values of the image with the values of other graphic elements
  • you need a different conversion matrix, for example colorimetric, perceptual, etc.

So the responsibility is yours. Not a random decision on a random process.

In so many cases when people ask (for example in this forum) what profile to use; if they are not aspiring professional graphics arts guys, I recommend that they don't do it, that they leave the RGB image and ask.

most rgb color profile gammut are bigger than what a printer can print anyway.

And this could be the other reason. There are clients, that could expect vibrant RGB colors when they can not be printed.


You have a secondary question:

So why does it matter if we start from RGB or CMYK since anyway we need to convert the color to XYZ before printing?

The answer is similar: Planning and control. This can even make a professional not choose CMYK but spot ink for example. Or even an additional print method, like silk print on top of the CMYK one!

Any professional, in any field, wants to reduce the unexpected variables as much as possible.


The questions from your comments.

I put some CMYK values in a picture/… will it actually be printed with this precise CMYK value?

It depends on the process. In some environments, like offset press, they should be used directly without any additional transformation. If you have a good relationship with the press bureau and the print company they could even inform you of some nuisances.

But in some other cases, mostly on generic print bureaus... Yes, 🤦🏻‍♀️ The driver, or the operator, or the lack of knowledge of the system, or for whatever reason... it could be transformed to RGB and then again into CMYK. So the keyword is "professional".

In most home and office environments the file will be most likely better as RGB.

If your project involves a decent number of digital copies, I would recommend that you send two versions of a test page, and decide.

One specific way to test if the print is using the specific values you have is by sending a pure yellow (c0m0Y100k0) some light oranges (c0m5y100k0) and some other incremental patches. The tiny magenta dots are easily differentiated.

You might need to see this image at 100%.

enter image description here

  • (A) The expected result. Clean pure yellow and incremental magenta.

  • (B) If the file is being transformed, it could be contaminated by some cyan.

  • (C) Or even by magenta, because we defined pure yellow on this first patch.


What if they have different printers with different ICC profiles

A digital print most likely will have its own profile. Even do some fancy separations, like a 6-color inkjet, where it has two cyans and two "blacks".

But sadly there is a lot, and I mean a lot of ignorance in the industry. In the decades I have been sending projects to different houses (sheetfed offset lithography), not one has given me a profile. Not that I need it, but as I start with a new provider I ask if they have one.

Most of the time they do not know even what I am talking about, so I use a generic one (according to the inks they use, on the part of the planet I am on) with 300% TAC or 240% on uncoated.

When a digital print, I send the two versions and send a sample test, before the project is sent.

But how can I even know the ICC profile of their printer?

My first question would be if you understand what a profile is.

It is the values the ink should have given a combination of the print process, inks, (environment), and... Paper!

  • If it is digital you do not know, and most likely you send it on RGB.
  • If they ask for CMYK you ask What profile?
  • If they do not know... Be patient... Remember we are talking about digital, so you can use a generic one with a high TAC, like Fogra 27 which has 350% TAC on coated paper.

If it is shifted offset, define the part of the planet where it will be printed. Mainly:

  • US-based: SWOP v2 or Gracol (coated or uncoated)
  • Europe-based: Eurocoated or Fogra (coated or uncoated, on Fogra notation the number defines the TAC based on the coating)
  • Japan-based: Japan (I don't remember)

As you can see, it is starting to become VERY specialized.

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    Also a very good answer! Responsibility and psychology plays a big role in printing. Mainly because it's a field where people with vastly different skill levels have to work together and try to secure smooth production without surprises.
    – Wolff
    Mar 2 at 17:08
  • Thanks a lot! But I'm confused: if I put some CMYK values in a picture/… will it actually be printed with this precise CMYK value? I would expect the ICC profile of the printer to be applied first, hence doing CMYK—XYZ—CMYK, and possibly losing some of the above mentionned benefits (e.g. pure cyan might not stay pure?)
    – tobiasBora
    Mar 2 at 18:50
  • Another nice question. It depends on the process. In some environments, like offset press, they should be used directly without any additional transformation. But in some other cases... Yes. Facepalm... The driver will transform it to RGB and then transform it again into CMYK. I will update my answer with this.
    – Rafael
    Mar 2 at 22:01
  • Thank you so much, your edit is extremely enlightening!
    – tobiasBora
    Mar 4 at 23:06
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    @Rafael - nice answer by the way.
    – Billy Kerr
    Mar 5 at 13:26
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RGB to CMYK is not a one to one conversion. Sure you can convert automatically but you may want to have control over the conversion. Reasons include but aren't limited to:

  • You may want to check that all values are in fact in the range of your device and adjust the overall space usage to match.

    Essentially when you say:

    absolute color representation in XYZ or CieLab, and the ICC profile of the printer should allow to convert an absolute XYZ to the printer-dependent CMYK color

    You are making the understatement of the year. In practice nobody uses absolute colorimeter transformation. What they do is one of the 3 other relative transforms instead since its way more useful and reflects better how humans expect things to happen.

    Ehat do we do with colors we can not convert. Just give up?

  • The automatic conversions are just one of the few possible ones, there are reasons why a expert might want to do something else.

  • You may want to control your black so it better matches body text (in this or another document)

    The CMYK space has much more nuanced options for black than your RGB document has. So you might want to convert your blacks to K only to have less problems with misalignment

  • You are the designer, it is your job to design the colors. Not some factory worker somewhere. If the company your using does not work the way you want get another service that does it for you.

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    +1! I can add a few more things you can do in CMYK which you can't do in RGB. Control C, M and Y: You can't make RGB colors which you can be sure will convert to specific CMYK tints. If you for example want clean 100% tints you need to specify colors in CMYK. 100% cyan even lies outside sRGB gamut. Multiple CMYK profiles: Sometimes you want to use a special CMYK profile for B&W images. You can't save this information in a PDF besides by doing the conversion manually. (And some more nerdy stuff I mention in this answer: graphicdesign.stackexchange.com/a/143349)
    – Wolff
    Mar 2 at 15:58
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    The last bullet in the answer is important. I do a lot of prepress and ... it's a jungle out there! It might sound harsh but most designers don't fully understand the technical aspects of printing. There's no money in educating every single one of them so you have to find solutions that work. Even if there are cleverer alternatives.
    – Wolff
    Mar 2 at 16:12
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    Forcing clients to deliver files in the correct CMYK profiles secures that they at least see some kind of CMYK preview of the file (although perhaps a wrong one). If we allowed people to just send RGB we would get complaints about vivid colors going dull. Teaching clients to use proper soft proofing is very hard and time consuming and we can't force them to download and install and use the correct profile.
    – Wolff
    Mar 2 at 16:12
  • Thanks a lot! But I'm confused: if I put some CMYK values in a picture/… will it actually be printed with this precise CMYK value? I would expect the ICC profile of the printer to be applied first, hence doing CMYK—XYZ—CMYK, and possibly losing some of the above mentionned benefits (e.g. pure cyan might not stay pure?)
    – tobiasBora
    Mar 2 at 18:52
  • @tobiasBora they are asking you to give the CMYK of their device yes
    – joojaa
    Mar 2 at 18:58

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