Finding and masking bright pixels

How to find and overplot the location of the brightest pixel and then mask pixels around that region.

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

import astropy.units as u

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

We start with the sample data.

aia = sunpy.map.Map(AIA_171_IMAGE)

To find the brightest pixel, we find the maximum in the AIA image data then transform that pixel coordinate to a map coordinate.

pixel_pos = np.argwhere(aia.data == aia.data.max()) * u.pixel
hpc_max = aia.wcs.pixel_to_world(pixel_pos[:, 1], pixel_pos[:, 0])

Let’s plot the results.

fig = plt.figure()
ax = fig.add_subplot(projection=aia)
aia.plot(axes=ax)
ax.plot_coord(hpc_max, color='white', marker='x', markersize=15)
plt.show()

A utility function gives us access to the helioprojective coordinate of each pixels. We create a new array which contains the normalized radial position for each pixel adjusted for the position of the brightest pixel (using hpc_max) and then create a new map.

hpc_coords = all_coordinates_from_map(aia)
r_mask = np.sqrt((hpc_coords.Tx - hpc_max.Tx) ** 2 +
                 (hpc_coords.Ty - hpc_max.Ty) ** 2) / aia.rsun_obs
mask = ma.masked_less_equal(r_mask, 0.1)
scaled_map = sunpy.map.Map(aia.data, aia.meta, mask=mask.mask)

Let’s plot the results.

fig = plt.figure()
ax = fig.add_subplot(projection=scaled_map)
scaled_map.plot(axes=ax)
plt.show()