  'PSF' menu help page


  The 'PSF' menu contains the following sub-menus:

  'Load':
      Load a PSF array from a FITS file.

  'Extract from image':
      Extract the PSF from the stellar field image, by superposition
      of a set of user-selected stars (referred to as 'PSF stars'). 
      This task may be used also to repeat the PSF extraction procedure 
      after analyzing the image, in order to improve the PSF estimate 
      using the available knowledge of the background emission and of 
      the secondary sources that contaminate the 'PSF stars'. 
 
  'Post process':
      Modify the support of the retrieved PSF and smooth the PSF halo.

  'Normalize':
      Normalize the PSF array to total flux = 1. This task may be useful
      to normalize an external PSF, loaded from a file. Notice that the
      PSF loaded, extracted or processed within XStarFinder is always 
      normalized automatically.

  'Save':
      Save to a FITS file the current estimate of the PSF.
