Astronomy example 1¶

Downloading images and writing `FITS` files¶

For examples, documentation, tutorials, etc, see Astropy at http://www.astropy.org

import numpy as np

import urllib                  # For retrieving an image from a URL

import matplotlib as mpl
import matplotlib.pyplot as plt

from PIL import Image
from astropy.io import fits
from astropy.utils.data import download_file
from astropy.visualization import astropy_mpl_style

# Following is an Ipython magic command that puts figures in the  notebook.
%matplotlib notebook 

# Following sets up LateX fonts
#mpl.rc('font', **{'family': 'serif', 'serif': ['Computer Modern']})
#mpl.rc('text', usetex=True)
#import matplotlib.image as mpimg
   
plt.style.use(astropy_mpl_style)

# M.L. modification of matplotlib defaults
# Changes can also be put in matplotlibrc file, 
# or effected using mpl.rcParams[]
plt.rc('figure', figsize = (6, 4.5))    # Reduces overall size of figures
plt.rc('axes', labelsize=14, titlesize=14)
plt.rc('xtick', labelsize=12)
plt.rc('ytick', labelsize=12)
plt.rc('figure', autolayout = True)  # Adjusts supblot parameters for new size

Retrieve and display a JPG image¶

Download image from the web, and store it as a local file
"Open" the image
Determine the size
Display

urllib.request.urlretrieve('http://www.eg.bucknell.edu/~mligare/Hs-2009-14-a-web.jpg','Hs-2009-14-a-web.jpg')
image = Image.open('Hs-2009-14-a-web.jpg')
xsize, ysize = image.size

plt.figure()
print("Image size: {} x {}".format(xsize, ysize))
plt.grid(color = 'w')
plt.imshow(image);

Image size: 400 x 232

Separate colors¶

r, g, b = image.split()
r_data = np.array(r.getdata()) # data is now an array of length ysize*xsize
g_data = np.array(g.getdata())
b_data = np.array(b.getdata())
print(r_data.shape)

(92800,)

r_data = r_data.reshape(ysize, xsize)
g_data = g_data.reshape(ysize, xsize)
b_data = b_data.reshape(ysize, xsize)

plt.figure()
plt.grid(color = 'b')
plt.imshow(r_data, cmap='Greys');

plt.figure()
plt.grid(color = 'b')
plt.imshow(g_data, cmap='Greys');

plt.figure()
plt.grid(color = 'b')
plt.imshow(b_data, cmap='Greys');

Write "FITS" files¶

red = fits.PrimaryHDU(data=r_data)
red.header['LATOBS'] = "32:11:56" # add spurious header info
red.header['LONGOBS'] = "110:56"
red.writeto('red.fits')

green = fits.PrimaryHDU(data=g_data)
green.header['LATOBS'] = "32:11:56"
green.header['LONGOBS'] = "110:56"
green.writeto('green.fits')

blue = fits.PrimaryHDU(data=b_data)
blue.header['LATOBS'] = "32:11:56"
blue.header['LONGOBS'] = "110:56"
blue.writeto('blue.fits')

Version Information¶

version_information is from J.R. Johansson (jrjohansson at gmail.com); see Introduction to scientific computing with Python for more information and instructions for package installation.

version_information is installed on the linux network at Bucknell

%load_ext version_information

%version_information numpy, matplotlib, astropy, PIL