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Beck04vall
Participant
February 21, 2018
Answered

How to setup Color Settings to perform a straight through RGB to CMY conversion?

  • February 21, 2018
  • 3 replies
  • 592 views

I've been doing a lot of reading regarding ICC profiles and workflows.  That said, I have a very specific use case that I would like help trying to achieve.  I'd like to be able to setup Photoshop to mimic / use a RGB to CMYK conversion that matches what our printer internal print engine is doing behind the scenes (in dev mode) to make image creation easier on my end.  The RGB to CMYK conversion is a simple straight through method (which I understand is not correct from a color perspective) where (255,0,0) RGB = (0,100,100,0) CMYK (following the EasyRGB method outline here: Math | EasyRGB ).  Obviously the K value need to be mapped to something, and can also use simple equations (such as that on the EasyRGB site for CMYK to CMY).

Is there a way to create a RGB and CMYK ICC profile such that this happens? I imagine they both need to specify the same gamut and the profiles just need to be inverse of the other if I'm understanding this correctly at all. I've been playing with making 'custom' profiles from the dialog available with no luck (although I have been able to get closer to what I want).

My check to see that this is working correctly is simply to open the color picker window and type in an value of (255,0,0)RGB and get (0,100,100,0)CMYK, which up to this point I can't.

Any help would be appreciated.

Thanks, -Dan

    This topic has been closed for replies.
    Correct answer D Fosse

    You cannot do this, it won't and can't work. And there's no reason to. This isn't nearly as complicated as you think.

    The only way to translate numerical values is through icc profiles. That's why the whole concept of color management and icc profiles was invented. The numbers have no meaning outside icc profiles.

    You just need to know which CMYK profile your printer wants. That's all there is to it. A simple conversion is all you need, all necessary parameters are built into the profile.

    3 replies

    Stephen Marsh
    Community Expert
    Stephen MarshCommunity Expert
    Community Expert
    February 22, 2018

    There is “visually correct” and there is also “numerically correct”…

    You could simply convert from RGB > Multichannel mode, then add a new 4th channel and ensure that it is white, then select mode > CMYK.

    However I doubt that this will be of great benefit, even if it does achieve your original request.

    D Fosse
    Community Expert
    D FosseCommunity Expert
    Community Expert
    February 21, 2018

    And just so we're clear: 255-0-0 does not translate into 0-100-100-0. You'd end up with a very different color. Again, it depends entirely on what specific profile those numbers refer to.

    T
    Test Screen Name
    Legend
    February 21, 2018

    In theory a profile could do all manner of incorrect or special putpose conversions. But this eeould be hard because (to oversimplify) the RGB profile will convert RGB to Lab, and the CMYK profile would convert Lab to CMYK. Now, I wouldn’t say it’s impossible for someone with a good understanding of colour science and profile intervals to do this but...

    D Fosse
    Community Expert
    D FosseCommunity ExpertCorrect answer
    Community Expert
    February 21, 2018

    You cannot do this, it won't and can't work. And there's no reason to. This isn't nearly as complicated as you think.

    The only way to translate numerical values is through icc profiles. That's why the whole concept of color management and icc profiles was invented. The numbers have no meaning outside icc profiles.

    You just need to know which CMYK profile your printer wants. That's all there is to it. A simple conversion is all you need, all necessary parameters are built into the profile.

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