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- Convert a 3-color image (JPG) to separate FITS images

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# Convert a 3-color image (JPG) to separate FITS images

This example opens an RGB JPEG image and writes out each channel as a separate FITS (image) file.

This example uses pillow to read the image, `matplotlib.pyplot` to display the image, and `astropy.io.fits` to save FITS files.

By: Erik Bray, Adrian Price-Whelan

License: BSD

    import matplotlib.pyplot as plt
    import numpy as np
    from PIL import Image

    from astropy.io import fits
    from astropy.visualization import astropy_mpl_style

Set up matplotlib and use a nicer set of plot parameters

    plt.style.use(astropy_mpl_style)

Load and display the original 3-color jpeg image:

    image = Image.open('Hs-2009-14-a-web.jpg')
    xsize, ysize = image.size
    print(f"Image size: {ysize} x {xsize}")
    print(f"Image bands: {image.getbands()}")
    ax = plt.imshow(image)

Out:

    Image size: 232 x 400
    Image bands: ('R', 'G', 'B')

Split the three channels (RGB) and get the data as Numpy arrays. The arrays are flattened, so they are 1-dimensional:

    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)

Out:

    (92800,)

Reshape the image arrays to be 2-dimensional:

    r_data = r_data.reshape(ysize, xsize) # data is now a matrix (ysize, xsize)
    g_data = g_data.reshape(ysize, xsize)
    b_data = b_data.reshape(ysize, xsize)
    print(r_data.shape)

Out:

    (232, 400)

Write out the channels as separate FITS images. Add and visualize header info

    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')

    from pprint import pprint

    pprint(red.header)

Out:

    SIMPLE  =                    T / conforms to FITS standard
    BITPIX  =                   64 / array data type
    NAXIS   =                    2 / number of array dimensions
    NAXIS1  =                  400
    NAXIS2  =                  232
    EXTEND  =                    T
    LATOBS  = '32:11:56'
    LONGOBS = '110:56  '

Delete the files created

    import os

    os.remove('red.fits')
    os.remove('green.fits')
    os.remove('blue.fits')

Total running time of the script: ( 0 minutes 0.156 seconds)

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