Removing Light Leak

In this example, we show how to remove the light leak (visible stray light) from XRT synoptic composite images.

from pathlib import Path

import matplotlib.pyplot as plt
import sunpy.map
from astropy.utils.data import get_pkg_data_path
from astropy.visualization import ImageNormalize, SqrtStretch

from xrtpy.image_correction import remove_lightleak

This example will be using XRT synoptic data from the first day of summer of 2015. This is stored in the example_data directory of the xrtpy package.

directory = get_pkg_data_path("data/example_data", package="xrtpy.image_correction")
data_file = Path(directory) / "comp_XRT20150621_055911.7.fits"
xrt_map = sunpy.map.Map(data_file)

Removing the light leak from the composite image is done using the xrtpy.image_correction.remove_lightleak function.

lightleak_map = remove_lightleak(xrt_map)

Finally, we plot the original and light leak subtracted images side by side.

fig = plt.figure(figsize=(12, 6))

ax = fig.add_subplot(121, projection=xrt_map)
xrt_map.plot(
    axes=ax,
    title="Original",
    norm=ImageNormalize(vmin=0, vmax=7e3, stretch=SqrtStretch()),
)
ax1 = fig.add_subplot(122, projection=lightleak_map)
lightleak_map.plot(
    axes=ax1,
    title="Light Leak Subtracted",
    norm=ImageNormalize(vmin=0, vmax=7e3, stretch=SqrtStretch()),
)

ax1.coords[1].set_ticks_visible(False)
ax1.coords[1].set_ticklabel_visible(False)
fig.tight_layout()

They look almost identical, but the light leak has been removed from the second image. To confirm this we can plot the difference between the two images.

diff_data = xrt_map.data - lightleak_map.data
# For this image, the difference is very small.
print(diff_data.min(), diff_data.max())

fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_title("Lightleak Difference")
im = ax.imshow(diff_data, origin="lower")
fig.colorbar(im)

plt.show()

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