saturation_image

  SATURATION_IMAGE - Scale an image to allow a saturation plot

  IM_OUT = SATURATION_IMAGE(IM_IN, ...)

  Scales the image to be in the range 2 ... ColorMapSize-1 so that
  color map entries 1 and ColorMapSize can be used for saturation values.

  If HighSaturation is Inf, then, at the high edge, the image is scaled from
  its empirical max to ColorMapSize-1. Otherwise, the image is scaled from
  the value HighSaturation onto ColorMapSize-1.

  If LowSaturation is -Inf, then the image is scaled from its empirical min
  to 2. Otherwise, the image is scaled from LowSaturation to 2.

  Example:
      myData = 40*membrane(1,25); % MathWorks logo
      myImage = saturation_image(myData,'LowSaturation',0,'HighSaturation',20);
      myColorMap = [ 0 0 0; jet(254); 1 1 1];
      figure;
      image(myImage);
      colormap(myColorMap);

  This function also takes name/value pairs that modifies its behavior:
  Parameter (default)   | Description
  ---------------------------------------------------------------------
  ColorMapSize (256)    | Size of the colormap; also, value used for the high
                        |   saturation index value
  HighSaturation (Inf)  | Value which, if exceeded, is set to be saturating
                        |   on the high side
  LowSaturation (-Inf)  | Value, which, if not achieved, is set to be 
                        |   saturating on the low side.
  LowSaturationValue (1)| Value used for the low saturation value
  NaNSaturation (1)     | Should NaN entries be set to Low (-1), High (1), or
                        |   be left alone (0)  ?