(*
  Fonction level
*)
let level (r, g, b) = (0.3 *. r +. 0.59 *. g +. 0.11 *. b) / 255

(*
  Fonction color2grey
*)
let color2grey (r, g, b) =
  let gr = (int)(level(r, g, b) *. 255.) in
    (gr, gr, gr)

(*
  Fonction image2grey src dst
*)
let image2grey scr dst =
  let (w,h) = get_dims img in
    for y = 0 to h do
      for x = 0 to w do
        Sdlvideo.put_pixel_color scr x y color2grey (Sdlvideo.get_pixel_color img x y)