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### CGASINHSCL

CGASINHSCL
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::
http://cheops1.uchicago.edu/idlhelp/sdssidl/plotting/tvasinh.html
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.)

## Categories

Image Processing

## Examples

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

## Author

FANNING SOFTWARE CONSULTING::
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

## History

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

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

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