# File lib/color/rgb.rb, line 168
  def to_cmyk
    c = 1.0 - @r.to_f
    m = 1.0 - @g.to_f
    y = 1.0 - @b.to_f

    k = [c, m, y].min
    k = k - (k * brightness)

    c = [1.0, [0.0, c - k].max].min
    m = [1.0, [0.0, m - k].max].min
    y = [1.0, [0.0, y - k].max].min
    k = [1.0, [0.0, k].max].min

    Color::CMYK.from_fraction(c, m, y, k)
  end