Port of https://gist.github.com/mailtruck/2411659 to Scala

ColorMeter.scala

object ColorMeter {

  def hexToRGB(hex: String): (Int,Int,Int) = {
    def toInt(str: String)(s: Int, e: Int) = 
      Integer.parseInt(str.substring(s,e), 16)

    val hex_1 = if (hex(0)=='#') hex.substring(1,7) else hex
    val r = toInt(hex_1)(0,2)
    val g = toInt(hex_1)(2,4)
    val b = toInt(hex_1)(4,6)
    (r, g, b)
  }

  def percents(rgb:(Int,Int,Int)):(Double,Double,Double) = {
    val p1 = (rgb._1 / 255d) * 100
    val p2 = (rgb._2 / 255d) * 100
    val p3 = (rgb._3 / 255d) * 100
    (p1,p2,p3)
  }

  def average(rgb:(Double,Double,Double)): Double = {
    math.round((rgb._1 + rgb._2 + rgb._3) / 3)
  }

  // 0 = same color; 100 = completely different, e.g. "000000" and "ffffff"
  def percentDifferent(cwith: String, ccolor: String): Double = {
    if (cwith.isEmpty && ccolor.isEmpty) 0d   // Entirely same
    if (cwith.isEmpty || ccolor.isEmpty) 100d // Entirely different
    else {  
      val rgb1 = percents(hexToRGB(cwith))
      val rgb2 = percents(hexToRGB(ccolor))
      math.abs(average(rgb1) - average(rgb2))
    }
  }
}