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T
Tank46
Participant
October 7, 2021
Answered

RGB and CMYK values

  • October 7, 2021
  • 3 replies
  • 713 views

I'm a bit confused. The RGB channels (with 256 default values per channel) produce 16,777,216 colors. If I follow that same computation with CMYK (with 100 values per ink color), it will produce 100,000,000 colors. However, CMYK cannot show all the colors RGB can. Where is my confusion coming from?

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Correct answer rob day

Also, you have to consider the reason for the 4th channel. CMYK inks are transparent, so 100% CMY is never close to absolute black, and there has to be the extra black plate in order to get a believable black appearance on press. That means there is a lot of redundancy in different 8-bit output values, which produce the same color appearance.

 

In this example we can see the GRACoL profiled CMYK channels are showing two very different CMYK output values, 58|38|14|1 on the left and 42|25|2|20 on the right. However, my #3 and #4 color samplers show that the colors have the same appearance assuming the press runs exactly to the GRACoL profile—their Lab values are both 60|0|-20:

 

 

 

 

3 replies

rob day
Community Expert
rob dayCommunity ExpertCorrect answer
Community Expert
October 14, 2021

Also, you have to consider the reason for the 4th channel. CMYK inks are transparent, so 100% CMY is never close to absolute black, and there has to be the extra black plate in order to get a believable black appearance on press. That means there is a lot of redundancy in different 8-bit output values, which produce the same color appearance.

 

In this example we can see the GRACoL profiled CMYK channels are showing two very different CMYK output values, 58|38|14|1 on the left and 42|25|2|20 on the right. However, my #3 and #4 color samplers show that the colors have the same appearance assuming the press runs exactly to the GRACoL profile—their Lab values are both 60|0|-20:

 

 

 

 

    T
    Tank46Author
    Participant
    October 17, 2021

    Thanks, Rob. Although the numbers may be confusing sometimes, following the standards will help me get my colors right.

    NB, colourmanagement
    Community Expert
    NB, colourmanagementCommunity Expert
    Community Expert
    October 7, 2021

    Hi, the discrete number of theoretical colours which can be defined within a color space such as RGB or CMYK is not related to the colour gamut (range of colour and tone). 

    If you swopped from 8 to 16 bit per channel you'd have a lot more possible definable colours but no change to the colour.

    8 bits will provide for 256 possible variations per channel, 16 bit will provide for 65,536 variations per channel.

    gamut essentially measures max possible saturation or density of colour . https://en.wikipedia.org/wiki/Gamut

     

    I hope this helps
    neil barstow, colourmanagement net :: adobe forum volunteer
    google me "neil barstow colourmanagement" for lots of free articles on colour management
    [please only use the blue reply button at the top of the page, this maintains the original thread title and chronological order of posts]

      T
      Tank46Author
      Participant
      October 12, 2021

      Hi Neil, yours and Mylenium's answers makes sense. I was messing with the numbers without understanding their basics.

      NB, colourmanagement
      Community Expert
      NB, colourmanagementCommunity Expert
      Community Expert
      October 14, 2021

      Tank, Hi, thanks for coming back to let us know we solved your conundrum.

       

      I hope this helps
      neil barstow, colourmanagement net :: adobe forum volunteer
      google me "neil barstow colourmanagement" for lots of free articles on colour management

      Mylenium
      Mylenium
      Legend
      October 7, 2021

      The math has nothing to do with actual color spaces or for that matter how realworld spectral frequencies and their interactions work. You learn that stuff in7th grade physics lessons when talking about light, absorption, reflection and all that good stuff. I would suggest you actually study up on this stuff on Wikipedia and other sites that explain things like XYZ Color space and the sub-sets such as RGB, CIELab and how it translates to physical reproduction processes such as CMYK printing. Similarly, there are enough articles out there that explain different color math in the computer way beyond your basic 8bit example and stuff liek color management, Gamma, effective gamut. You really need to take a broader approach. None of this can be explained in a few simple sentences.

       

      Mylenium

        T
        Tank46Author
        Participant
        October 12, 2021

        Thanks, Mylenium! I really do need to read more on this.

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