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J
Jack03
Participating Frequently
October 15, 2020
Question

RGB to CMYK : 2 different cases with 2 different results when printed

  • October 15, 2020
  • 6 replies
  • 6733 views

Hello,

 

I have an image (a drawing) in RGB.

For printing purposes, I have to convert it to CMYK.

So here is what I did:

Case n °1
I open the RGB file and go to Image > Mode > and switch to CMYK.
I print it.

Case n °2
I create a blank CMYK file and paste the layers of the RGB drawing into it.

And I print.

While the 2 documents are now in CMYK, I have huge differences when printed.

Converting directly to CMYK (case 1) darkens the design a lot when printed, whereas importing the RGB layers into a blank CMYK document (case 2) leads to nearly the same color as the printed RGB.

I'm attaching 2 images:
- 1st one is to see the CMYK differences when printed (case 1 and case 2)
- the 2nd one is to see that RBG and case 2 printed out are very similar.

Can someone help me to understand those differences, and what should I do have perfect printed colors ?

Many thanks !

 

 

[Typo in subject line corrected from "RGB to CMJN" to "RGB to CMYK" by moderator.]

 

 

This topic has been closed for replies.

6 replies

J
Jack03Author
Participating Frequently
October 24, 2020

Hello,

Does anyone know what I can do  regarding this last problem:

 

 

To show you, I made this screenshot (before I placed a white background to all images to be able to compare):

Left: RGB
Middle: CMYK with merged layers before CMYK conversion
Right: CMYK with flatten image before CMYK conversion


If I flatten the file before CMYK color conversion, it looks great but it removes the transparency which I need to keep.

If I don't flatten it and just merge layers, color conversion will darken the design (even change a bit the color), but I will keep the transparency.

Many thanks

T
Test Screen Name
Legend
October 24, 2020

Transparency WILL be different between CMYK and RGB. What aspect of the transparency do you need to keep? 

J
Jack03Author
Participating Frequently
October 24, 2020

Hello,

I need to convert RGB to CMYK.

If I flatten the file before CMYK color conversion, it looks great but it removes the transparency which I need to keep.
If I don't flatten it and just merge layers, color conversion will darken the design (even change a bit the color itself), but I will keep the transparency.

I would need the converted colors of the flatten image (which is very close from RGB color), but I also need transparency so I don't know what to do here.

J
Jack03Author
Participating Frequently
October 17, 2020

Hello,

 

Alright, however the printer asked for CMYK files.

So should I convert to Japan profile directly ?

I guess I should.

 

thanks

J
Jack03Author
Participating Frequently
October 17, 2020

Hello,

Here is an update.

When I send my files to the printer, he has an inhouse designer that will set an .AI file with all my artworks organised on it and send it to print.

I finally got his file this morning and I have checked the CMYK profile he used, it is "Japan Color 2001 Coated CMYK profile" (the printer is in Asia).

So I suppose I have to pick the same profile ?

I won't be able to have more information on it, as the designer don't speak english at all 😞

How does it sound ?

Many thanks.

D Fosse
Community Expert
D FosseCommunity Expert
Community Expert
October 17, 2020

In that case I don't understand why the designer shouldn't do the final conversion to CMYK. That would be the normal and standard procedure, used everywhere else, and you'd just provide RGB originals.

 

A press-ready PDF is normally produced in InDesign, but I suppose it's possible with Illustrator as well.

 

A great advantage of doing it this way is flexibility. If press conditions change (new printer etc), it's just a matter of exporting a new PDF to new specifications.

 

I suspect there's a misunderstanding here, perhaps something lost in translation. Again, there is absolutely no reason you should send CMYK. One point to note is that CMYK to CMYK conversions should always be avoided, for many reasons.

 

Still, knowing the final profile is an advantage. That means you can soft proof to it, and so anticipate any gamut clipping in the print process. If you see any, you can try to compensate for it.

 

 

    NB, colourmanagement
    Community Expert
    NB, colourmanagementCommunity Expert
    Community Expert
    October 16, 2020

    Using "generic CMYK" is a very poor way to work, its also risky to guess at Swop coated (Photoshop's default).

    Printing press output depends on how the press is run - also on inks, substrate and the way the plates are made. These days there are ISO standard press conditions, described by ICC profiles such as those from GRACoL and from the ECI / FOGRA in Europe. 

     

    If you are working with a printer who cannot give you an ICC profile to describe the process then you are effectively throwing a dart at a dartboard in the dark and hoping to hit the bullseye.

    Guessing what CMYK to use is like sending a letter only knowing the town & guessing the street address and zipcode. 

     

    You could ask the printer for their experience with received files., When files are received at the printers, they will predominantly have an embedded ICC CMYK profile.

    Ask them this - looking at the files which were received and printed successfully, what was the ICC profile most commonly embedded. 

    It seems you ideally need a better more modern printer - or the printer really needs to catch up with the way good standardized printing is done these days.

    It's amazing the "just use generic CMYK" guys are still in business.

     

    I hope this helps

    thanks
    neil barstow, colourmanagement.net :: adobe forum volunteer
    [please do not use the reply button on a message within the thread, only use the blue reply button at the top of the page, this maintains the original thread title and chronological order of posts]

    T
    Test Screen Name
    Legend
    October 15, 2020

    Darkening is correct. Paste is not colour managed so it cannot give accurate colour, even if by good luck it seems to be what you want. How is it printed, and what CMYK profile do you use?

      J
      Jack03Author
      Participating Frequently
      October 15, 2020

      Hello,

       

      Thank you for your reply.

      OK so now I know I should use Image > Mode to change to CMYK.

      It will be printed at a professional offset printing company, and I use generic CMYK profile.

      Now I've tested a new case 🙂
      1. I open the RGB file
      2. I flatten all visible layers
      3. then Image > Mode > and I pick CMYK

      I print this file, and it is very very close to the printed RGB, not dark as it was before.

      I've seen on adobe website that they recommand to flatten the layers before changing the color mode:

      in most cases, it is best to flatten a file before converting it. However, this is not required and in some cases it is not even desirable (when the file contains vector text layers, for example).


      Do you think it is good if I do like it ?

      Many thanks.

      J
      Jack03Author
      Participating Frequently
      October 15, 2020

      Here is the link on adobe:
      https://helpx.adobe.com/photoshop/using/converting-color-modes.html

      "Flatten the file before converting it. The interaction of colors between layer blending modes changes when the mode changes."

      D Fosse
      Community Expert
      D FosseCommunity Expert
      Community Expert
      October 15, 2020

      The short answer here is that CMYK is wrong. Don't do it. CMYK is for commercial offset printing only. Inkjet/desktop printers are RGB devices that expect RGB data.

       

      Second, if you should ever need to work in CMYK, you need the actual CMYK profile. There is no such thing as a generic CMYK. Image > Mode just gives you whatever is set up as working CMYK, which most likely isn't the correct one. To work in CMYK, you really need to know what you're doing.

       

      As for printer color management in general, you set this up in the Photoshop print dialog. Leave the document color space as it is. Pick the correct print profile for the printer and paper you're using. Then go into the printer driver and pick the correct media type there. Also turn printer color management off.

       

      A simpler, but less accurate way, is to set "Printer manages color" instead of "Photoshop manages color". Then it's all handled in the printer driver, but you still have to pick the correct media type (paper).

        J
        Jack03Author
        Participating Frequently
        October 15, 2020

        Hello,

        Thank you for your reply.

        Yes, I should have been more precise.

        The file will be send to a professional printer that needs CMYK.

        Jacqyes

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