Convert RGB to CMYK in Delphi script

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;

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;