Command-line Scripts

Astroimtools installs a couple of useful utility programs for calculating image statistics and simple arithmetic.

imarith

imarith is a command-line script based on astroimtools.nddata_arith for performing basic arithmetic on arrays extracted from two FITS files. The arithmetic is performed for the data in only a single FITS extension in both FITS file.

Example usage:

  1. Add the array in extension 1 of the first FITS file with extension 3 in the second FITS file, placing the result in “result.fits”:

    $ imarith filename1.fits filename2.fits '+' -e1 1 -e2 3 -o 'result.fits'
    
  2. Perform the same operation above, but also add the exposure time values in the headers of the FITS files, placing the result in “result.fits”:

    $ imarith filename1.fits filename2.fits '+' -e1 1 -e2 3 -k 'exptime' -o 'result.fits'
    

imstats

imstats is a command-line script based on astroimtools.nddata_stats to calculate various statistics of an array from a single extension of a FITS file. Sigma-clipped statistics can be calculated by specifying the sigma option.

The currently available statistics are:

  • 'mean'

  • 'median'

  • 'mode'

  • 'std'

  • 'mad_std'

  • 'npixels' (for sigma-clipped statistics)

  • 'nrejected' (for sigma-clipped statistics)

  • 'min'

  • 'max'

  • 'biweight_location'

  • 'biweight_midvariance'

  • 'kurtosis'

  • 'skew'

Example usage:

  1. Calculate simple image statistics on the data in the first FITS extension:

    $ imstats filename.fits -e 1
    
      filename    npixels   mean    std     min      max
    ------------- ------- -------- ------ -------- -------
    filename.fits 1027865 0.438514 0.6974 -59.8228 65.8734
    
  2. Same as above, but specify different statistics:

    $ imstats filename.fits -e 1 --columns 'mean, mode, std, mad_std'
    
      filename      mean    mode   std   mad_std
    ------------- -------- ------ ------ -------
    filename.fits 0.438514 0.4271 0.6974 0.68134
    
  3. Calculate sigma-clipped (at 3 standard deviations) image statistics on the data in the first FITS extension:

    $ imstats filename.fits -e 1 -sigma 3
    
      filename    npixels   mean    std     min      max
    ------------- ------- -------- ------ -------- -------
    filename.fits 1020413 0.425871 0.5742 -39.2302 55.2304