Read and plot an image from a FITS file

This example opens an image stored in a FITS file and displays it to the screen.

This example uses astropy.utils.data to download the file, astropy.io.fits to open the file, and matplotlib.pyplot to dispay the image.

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By: Lia R. Corrales, Adrian Price-Whelan, Kelle Cruz

License: BSD

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Set up matplotlib and use a nicer set of plot parameters

import matplotlib.pyplot as plt
from astropy.visualization import astropy_mpl_style
plt.style.use(astropy_mpl_style)

Download the example FITS files used by this example:

from astropy.utils.data import download_file
from astropy.io import fits

image_file = download_file('http://data.astropy.org/tutorials/FITS-images/HorseHead.fits',
                           cache=True)

Out:

Downloading http://data.astropy.org/tutorials/FITS-images/HorseHead.fits [Done]

Use astropy.io.fits.info() to display the structure of the file:

fits.info(image_file)

Out:

  Filename: /home/docs/.astropy/cache/download/py2/2c9202ae878ecfcb60878ceb63837f5f
No.    Name         Type      Cards   Dimensions   Format
0    PRIMARY     PrimaryHDU     161   (891, 893)   int16
1    er.mask     TableHDU        25   1600R x 4C   [F6.2, F6.2, F6.2, F6.2]

Generally the image information is located in the Primary HDU, also known as extension 0. Here, we use astropy.io.fits.getdata() to read the image data from this first extension using the keyword argument ext=0:

image_data = fits.getdata(image_file, ext=0)

The data is now stored as a 2D numpy array. Print the dimensions using the shape attribute:

print(image_data.shape)

Out:

(893, 891)

Display the image data:

plt.figure()
plt.imshow(image_data, cmap='gray')
plt.colorbar()

Total running time of the script: (0 minutes 0.397 seconds)

Download Python source code: plot_fits-image.py

Download IPython notebook: plot_fits-image.ipynb