Masking out the solar disk

How to mask out all emission from the solar disk.

import numpy as np
import numpy.ma as ma
import matplotlib.pyplot as plt

import astropy.units as u

import sunpy.map
from sunpy.data.sample import AIA_171_IMAGE

We start with the sample data

aia = sunpy.map.Map(AIA_171_IMAGE)

Next, we create arrays for all of the pixels in the map.

x, y = np.meshgrid(*[np.arange(v.value) for v in aia.dimensions]) * u.pixel

Next we can convert all of the pixels coordinates to helioprojective coordinates and create a new array which contains the normalized radial position for each pixel.

hpc_coords = aia.pixel_to_world(x, y)
r = np.sqrt(hpc_coords.Tx ** 2 + hpc_coords.Ty ** 2) / aia.rsun_obs

With this information, we create a mask where all values which are less then the solar radius are masked. We also make a slight change to the colormap so that masked values are shown as black instead of the default white.

mask = ma.masked_less_equal(r, 1)
palette = aia.plot_settings['cmap']
palette.set_bad('black')

Finally we create a new map with our new mask.

scaled_map = sunpy.map.Map(aia.data, aia.meta, mask=mask.mask)

Let’s plot the results using our modified colormap

fig = plt.figure()
plt.subplot(projection=scaled_map)
scaled_map.plot(cmap=palette)
scaled_map.draw_limb()
plt.show()
../../../_images/sphx_glr_mask_disk_001.png

Total running time of the script: ( 0 minutes 0.784 seconds)

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