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  This is a utility routine to perform standard deviation scaling
  on image arrays. The user defines a multiple of the standard
  deviation and this is used with the standard deviation of the
  pixels in the image to create a threshold for linear scaling.
  Use the EXCLUDE keyword to exclude a particular value from
  the standard deviation calculation.


    Utilities, Graphics


    image: in, required, type=numeric
        The image array that is to be scaled.


    exclude: in, optional, type=numeric
        Set this keyword to a value in the image array that is to be excluded from the
        standard deviation calculation. Normally, this would be the backgroud value of
        the image, if there is a background.
    multiplier: in, optional, type=float, default=2.0
        The standard deviation of the image pixels is computed and then
        multiplied by the multiplier factor to produce upper and lower
        thresholds for the linear scaling of the image by subtracting
        or adding this value to the mean value of the image. The image
        is linearly scaled between these two threshold values.
    negative: in, optional, type=boolean
          Set this keyword to return the "negative" or reverse of the image scaling.
    omax: in, optional, type=byte, default=255
          Normally, the image is scaled into the range of 0 to 255. Setting the
          OMIN and OMAX keywords can change this scaling.
    omin: in, optional, type=byte, default=0
          Normally, the image is scaled into the range of 0 to 255. Setting the
          OMIN and OMAX keywords can change this scaling.
    threshold: out, optional, type=float
          A two-element array that contains the minimum and maximum thresholds, respectively,
          that were calculated for the scaling.


    To display an image with standard deviation scaling::
        image = cgDemoData(5)
        cgDisplay, 256*3, 256
        !P.Multi = [0,3,1]
        cgImage, image
        cgImage, SDevScl(image)
        cgImage, SDevScl(image, Exclude=0)
        !P.Multi = 0


        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, 5 June 2012.
        Renamed cgSDevScl from SDevScl. 27 Mar 2015. DWF.


    Copyright (c) 2012, Fanning Software Consulting, Inc.

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