coyote: CGRESIZERASTER

Description
The purpose of this program is to resize a raster file according to 
instructions from the user. It was designed specifically to resize the
extremely large raster files created by IDL's function graphics commands
from within an IDL program. It requires ImageMagick be installed and able
to be called from a SPAWN command from within IDL.
Categories
Graphics
Params
rasterfile: in, required, type=string
     Set this parameter to the name of the raster file to be resized. The resized
     file will have this same name unless the `KEEP_ORIGINAL` keyword is set, in
     which case an "_rs" will be appended to the base name given by this parameter.
percentage: in, optional, type=float
     A resize percentage. A value of 50, for example, will make the output file
     half its original size. A file may be made bigger by specifying a percentage
     greater than 100 (e.g. 150). The default is to calculate a precentage that makes
     the longest dimension of the output file approximately 600 pixels.
Keywords
keep_original: in, optional, type=boolean
     Set this keyword to keep the original file. Otherwise, the file is overwritten with
     the resized file. If this keyword is set, the output file will use the same name as
     the input file, except an "_rs" will be appended to the base name of the input file.
height: in, optional, type=integer
     Set this keyword to set the height of the resulting raster file in pixel units. The width of the
     raster will be such as to preserve the aspect ratio of the starting image. This keyword
     cannot be used if the `WIDTH` keyword is used at the same time.
silent: in, optional, type=boolean, default=0
     Set this keyword to suppress printed output from the program. 
width: in, optional, type=integer
     Set this keyword to set the resulting width of the raster file. The height of the
     raster will be such as to preserve the aspect ratio of the starting image. This keyword
     cannot be used if the `HEIGHT` keyword is used at the same time.
Examples
Here is how to use this program::
   IDL> cgResizeRaster, 'picture.png', /Keep_Original, Width=500
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, 15 January 2014 by David W. Fanning.
Copyright
Copyright (c) 2014, Fanning Software Consulting, Inc.