Convert RGB to HSL color model

rgb2hsl.rb

def rgb2hsl(r,g,b)
  r´ = r.to_f / 255
  g´ = g.to_f / 255
  b´ = b.to_f / 255
  c_max = [r´, g´, b´].max
  c_min = [r´, g´, b´].min
  Δ = c_max - c_min
  h = Δ.zero? ? 0 : (60 * case c_max
    when r´ then ((g´ - b´) / Δ) % 6
    when g´ then ((b´ - r´) / Δ) + 2
    when b´ then ((r´ - g´) / Δ) + 4
  end)
 l = (c_max + c_min) / 2
 s = Δ.zero? ? 0 : (Δ / (1 - (2 * l - 1).abs))

 [h.round(0), s.round(2), l.round(2)]
end

http://www.w3.org/TR/2011/REC-css3-color-20110607/#hsl-color
http://axonflux.com/handy-rgb-to-hsl-and-rgb-to-hsv-color-model-c
http://colorizer.org/