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  This is a utility routine to perform an inverse hyperbolic sine
  function intensity transformation on an image. I think of this
  as a sort of "tuned" gamma or power-law function. The algorithm,
  and notion of "asinh magnitudes", comes from a paper by Lupton,
  et. al, in The Astronomical Journal, 118:1406-1410, 1999 September.
  I've relied on the implementation of Erin Sheldon, found here::
  I'm also grateful of discussions with Marshall Perrin on the IDL
  newsgroup with respect to the meaning of the "softening parameter", beta,
  and for finding (and fixing!) small problems with the code.
  Essentially this transformation allow linear scaling of noise values,
  and logarithmic scaling of signal values, since there is a small
  linear portion of the curve and a much large logarithmic portion of
  the curve. (See the EXAMPLE section for some tips on how to view this
  transformation curve.)


    Image Processing


    Plot various values of beta::
        cgPlot, cgASinhScl(Indgen(256), Beta=0.0), LineStyle=0
        cgOPlot, cgASinhScl(Indgen(256), Beta=0.1), LineStyle=1
        cgOPlot, cgASinhScl(Indgen(256), Beta=1.0), LineStyle=2
        cgOPlot, cgASinhScl(Indgen(256), Beta=10.), LineStyle=3
        cgOPlot, cgASinhScl(Indgen(256), Beta=100), LineStyle=4


          David W. Fanning
          1645 Sheely Drive
          Fort Collins, CO 80526 USA
          Phone: 970-221-0438
          E-mail: david@idlcoyote.com
          Coyote's Guide to IDL Programming: http://www.idlcoyote.com


    Change History::
      Written by: David W. Fanning, 24 February 2006.
      Removed ALPHA keyword and redefined the BETA keyword to correspond
        to the "softening parameter" of Lupton et. al., following the
        suggestions of Marshall Perrin. 25 April 2006. DWF.
      Renamed cgASinhScl from ASinhScl. 27 March 2015. DWF.
      Missed a couple of retire program name changes in the program. 7 April 2015. DWF.


    Copyright (c) 2008-2015, Fanning Software Consulting, Inc.

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