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The CMYK (Cyan, Magenta, Yellow, Black - Key Plate) model, refers to the 4 ink colors used by the printing press. C is cyan (blue-green), M is magenta (pinkish shade of red), Y is yellow, and K is black, the key plate or keyline color.

The RGB (Red, Green, Blue) is also used, primarily in web design. When written, RGB values are commonly specified using three integers between 0 and 255, each representing red, green, and blue intensities.

Converting RGB images to CMYK is often one of the final steps before sending an image to a commercial printer.

Here's a function to convert a RGB color to a CMYK color.

uses Math;

function RGBtoCMYK(const rgbColor : TRGBColor) : TCMYKColor;
begin
  with Result do
  begin
    Cyan := 1 - rgbColor.Red;
    Magenta := 1 - rgbColor.Green;
    Yellow := 1 - rgbColor.Blue;

    KeyPlate := Min(Min(Cyan, Magenta), Yellow) ;

    Cyan := Cyan - KeyPlate;
    Magenta := Magenta - KeyPlate;
    Yellow := Yellow - KeyPlate;
  end;
end;

Usage:

var
  rgbColor : TRGBColor;
  cmykColor : TCMYKColor;
begin
  rgbColor.Red := 128;
  rgbColor.Green := 64;
  rgbColor.Blue := 192;

  cmykColor := RGBtoCMYK(rgbColor) ;

  Caption := Format('%d-%d-%d-%d',[cmykColor.Cyan, cmykColor.Magenta, cmykColor.Yellow, cmykColor.KeyPlate])
end;

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