Public Function RGBToHSL201(ByVal RGBValue As Long) As HSL
' by Donald, donald@xbeat.net, 20011126
  Dim R As Long, G As Long, b As Long
  Dim lMax As Long, lMin As Long, lDiff As Long, lSum As Long

  R = RGBValue And &HFF&
  G = (RGBValue And &HFF00&) \ &H100&
  b = (RGBValue And &HFF0000) \ &H10000

  If R > G Then lMax = R: lMin = G Else lMax = G: lMin = R
  If b > lMax Then lMax = b Else If b < lMin Then lMin = b

  lDiff = lMax - lMin
  lSum = lMax + lMin
  
  ' Luminance
  RGBToHSL201.Luminance = lSum / 5.1!
  
  If lDiff Then
    ' Saturation
    If RGBToHSL201.Luminance <= 50& Then
      RGBToHSL201.Saturation = 100 * lDiff / lSum
    Else
      RGBToHSL201.Saturation = 100 * lDiff / (510 - lSum)
    End If
    ' Hue
    Dim q As Single: q = 60 / lDiff
    Select Case lMax
    Case R
      If G < b Then
        RGBToHSL201.Hue = 360& + q * (G - b)
      Else
        RGBToHSL201.Hue = q * (G - b)
      End If
    Case G
      RGBToHSL201.Hue = 120& + q * (b - R)
    Case b
      RGBToHSL201.Hue = 240& + q * (R - G)
    End Select
  End If
  
End Function