*isoreg* - A region defined by an isointensity contour

A region file can be made which defines the region enclosed within a specific intensity level contour. First the image must be smoothed:

  cl> xray
  xr> xspatial
  xs> imsmooth ``xdata$snr.qp(400:600,400:600)'' snr gaus 5  # output is snr_smo.imh
  xs> isoreg xnr_smo snr 0.2                                  # output is snr_iso.pl
  xs> pllist snr_iso.pl                                            # shows the mask.