It not need to be so precise, even because it can change depending on color profile, but I would like to know if there is some formula/algorithm that receive the percentage of C, M, Y and K, then return true or false if it is rich black color.

for example C=70 M=60 Y=40 K=80 TRUE and C=10 M=80 Y=100 K=85 FALSE

I need it to create an Illustrator script to replace the color of texts that is almost black (rich black) to only K.

  • 1
    Printers often use 240 as a cutoff point for registration black (i.e., if all four values add up to >240, it’s registration black) – is that what you mean? ‘Rich black’ is quite a vague term, and most uses of what I would call rich black involve K100. Commented Dec 22, 2020 at 9:01
  • If K = 100 AND C+M+Y+K>100 AND C+M+Y+K<241 then True. Both your examples would be false.
    – Billy Kerr
    Commented Dec 22, 2020 at 13:01
  • @JanusBahsJacquet. A rich black doesn't have to have K=100%. An automatic conversion from RGB black to CMYK would give the darkest possible black within that CMYK profile and could be said to be "rich black". It seldom has 100% black.
    – Wolff
    Commented Dec 22, 2020 at 14:12
  • Hello @JanusBahsJacquet, 'rich black' I mean any color that seems black but is not only composite by K. I was wondering if there is some formula that recognize it because this > 240 sometimes returns a false positive Commented Dec 24, 2020 at 8:29
  • @AlanAlvesdeOliveira I don't think there's a formula on the device CMYK values. Simply because different printers produce different colors for same CMYK values because their inks/paper differs. So definitely saying something is rich black form CMYK values alone is very very sketchy to begin with. What you would do is convert the cmyk values to LAB with a profile aware conversion. Then you can say something.
    – joojaa
    Commented Dec 24, 2020 at 9:18

1 Answer 1


Using Adobe Acrobat you can determine which color channels will be printed at any point in your document. Open the Print Production/Output Preview tool:

print production window

When you hover the mouse over an area, the cmyk vpercentage values are displayed in the tool window.

In addition you can automatically highlight (in this case red, but you can change the highlight color) sections of your document that have an area coverage greater than i.e. 200% (you can determine the value via the dropdown menu).

highlight total area coverage

As @Janus mentioned in his comment, Printers often set the max area coverage at around 240/260% to avoid the stock being soaked in too much ink, which could cause deformation ect.

  • Hey Dom, I don't think this is what is being asked. The OP wants an algorithm/formula to check if a CMYK colour is considered to be "rich black" or not.
    – Billy Kerr
    Commented Dec 22, 2020 at 12:08
  • Thanks! but what I'm looking for is actually something that judge if the color is or not rick black Commented Dec 24, 2020 at 8:38

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