NAME:
  image2hull
 PURPOSE:   (one line only)
  Convert a bit-mapped image of an object to a hull
 DESCRIPTION:
 CATEGORY:
  Occultations
 CALLING SEQUENCE:
   image2hull,image,hx,hy
 INPUTS:
   image - 2-d array that is expected to be an image of an object (real or
             syntethic)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
   hx - X position of a point on the exterior hull of the object
   hy - Y position of a point on the exterior hull of the object
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
   Interior openings are ignored.  There is an internal scaling to a 1-bit
   image and this scaling is not yet generalized.
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2023/08/21