NAME:
  seeing
 PURPOSE:   (one line only)
  Given an astronomical image, determine the image quality (seeing).
 DESCRIPTION:
 CATEGORY:
  CCD data processing
 CALLING SEQUENCE:
  seeing,image,fwhm,objrad,nstars
 INPUTS:
  image - Array containing image to be examined.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  FWHMGUESS - Initial guess of the FWHM in the image.  Default=3.  If this
                 is significantly smaller than the actual seeing you will
                 get an answer that is much too small.  The penalty for
                 guessing a larger than optimal value appears to be weak.
  MINSIGNAL - minimum signal to consider when looking for sources
                 (default=0)
  MAXSIGNAL - maximum signal to conisder when looking for sources
                 (default=60000)
  NODISPLAY - Flag, if set will suppress plot and image outputs
 OUTPUTS:
  fwhm  - Image quality, FWHM in pixels for the image.
  objrad - Object aperture radius used to determine fwhm
  nstars - Number of stars that were averaged to get fwhm
 KEYWORD OUTPUT PARAMETERS:
  ERROR - set to 1 (true) if an error occurred, zero otherwise.  If the
            error flag is set, the return values may or may not be useful.
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Lowell Observatory, 2004/07/03
  2005/06/28, MWB, added extra error trapping and ERROR keyword
  2008/07/23, MWB, added keyword for initial FWHM guess