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 display the image.

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

License: BSD

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

image_file = get_pkg_data_filename('tutorials/FITS-images/HorseHead.fits')

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

fits.info(image_file)

Filename: /home/user/.astropy/cache/download/url/ff6e0b93871033c68022ca026a956d87/contents
No.    Name      Ver    Type      Cards   Dimensions   Format
  0  PRIMARY       1 PrimaryHDU     161   (891, 893)   int16
  1  er.mask       1 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)

(893, 891)

Display the image data:

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

<matplotlib.colorbar.Colorbar object at 0x7fd7955cb7d0>