# Recipe 37: Posterise a picture

def posterise(picture):

  # Loop through the pixels
  for p in getPixels(picture):

    # Get the RGB values
    red = getRed(p)
    green = getGreen(p)
    blue = getBlue(p)

    # Check and set red values
    if (red < 64):
      setRed(p, 31)
    if (red > 63 and red < 128):
      setRed(p, 95)
    if (red > 127 and red < 192):
      setRed(p, 159)
    if (red > 191 and red < 256):
      setRed(p, 223)

    # Check and set green values
    if (green < 64):
      setGreen(p, 31)
    if (green > 63 and green < 128):
      setGreen(p, 95)
    if (green > 127 and green < 192):
      setGreen(p, 159)
    if (green > 191 and green < 256):
      setGreen(p, 223)

    # Check and set blue values
    if (blue < 64):
      setBlue(p, 31)
    if (blue > 63 and blue < 128):
      setBlue(p, 95)
    if (blue > 127 and blue < 192):
      setBlue(p, 159)
    if (blue > 191 and blue < 256):
      setBlue(p, 223)