RGB to CMYK (rough)

rgbcmyk.js

function rgbtocmyk(r, g, b) {
  
  if (!r && !g && !b) {
    return [0, 0, 0, 1]
  }
  
  var c = m = y = k = 0;

  c = 1 - (r/255);
  m = 1 - (g/255);
  y = 1 - (b/255);

  var min = Math.min(Math.min(c, m), y);
  var denom = 1 - min;
  c = (c - min) / denom;
  m = (m - min) / denom;
  y = (y - min) / denom;
  k = min;
  
  return [c, m, y, k];
  
}