FIND

       Find positive brightness perturbations (i.e stars) in an image

       Also returns centroids and shape parameters (roundness & sharpness).
       Adapted from 1986 STSDAS version of DAOPHOT.

       FIND, image, [ x, y, flux, sharp, round, hmin, fwhm, roundlim, sharplim
               PRINT= , /SILENT ]

       image - 2 dimensional image array (integer or real) for which one
               wishes to identify the stars present

       FIND will prompt for these parameters if not supplied
       hmin -  Threshold intensity for a point source - should generally
               be 3 or 4 sigma above background
       fwhm  - FWHM to be used in the convolve filter
       sharplim - 2 element vector giving low and high cutoff for the
               sharpness statistic (Default: [0.2,1.0] ).   Change this
               default only if the stars have significantly larger or
               or smaller concentration than a Gaussian
       roundlim - 2 element vector giving low and high cutoff for the
               roundness statistic (Default: [-1.0,1.0] ).   Change this
               default only if the stars are significantly elongated.

       /SILENT - Normally, FIND will write out each star that meets all
               selection criteria.   If the SILENT keyword is set and
               non-zero, then this printout is suppressed.
       PRINT - if set and non-zero then FIND will also write its results to
               a file find.prt.   Also one can specify a different output file
               name by setting PRINT = 'filename'.

       x - vector containing x position of all stars identified by FIND
       y-  vector containing y position of all stars identified by FIND
       flux - vector containing flux of identified stars as determined
               by a Gaussian fit.  Fluxes are NOT converted to magnitudes.
       sharp - vector containing sharpness statistic for identified stars
       round - vector containing roundness statistic for identified stars

       (1) The sharpness statistic compares the central pixel to the mean of
       the surrounding pixels.   If this difference is greater than the
       originally estimated height of the Gaussian or less than 0.2 the height of the
       Gaussian (for the default values of SHARPLIM) then the star will be
       rejected.
       (2) More recent versions of FIND in DAOPHOT allow the possibility of
       ignoring bad pixels.    Unfortunately, to implement this in IDL
       would preclude the vectorization made possible with the CONVOL function
       and would run extremely slowly.

       GETOPT()

       Written W. Landsman, STX  February, 1987
       ROUND now an internal function in V3.1   W. Landsman July 1993
       Change variable name DERIV to DERIVAT    W. Landsman Feb. 1996
       Use /PRINT keyword instead of TEXTOUT    W. Landsman May  1996
       Changed loop indices to type LONG       W. Landsman Aug. 1997
       Converted to IDL V5.0   W. Landsman   September 1997
       Replace DATATYPE() with size(/TNAME)   W. Landsman Nov. 2001
       Fix problem when PRINT= filename   W. Landsman   October 2002
       Fix problems with >32767 stars   D. Schlegel/W. Landsman Sep. 2004

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