Example of converting an asymmetry score map into a binary ionization map (top panel), and converting an ionization map into a binary ionization map (bottom panel). The left column shows the original maps. The second column shows the maps converted into binary maps by setting all the pixels with asymmetry score ($\overline{x}$) above (below) a threshold ionized. The third column shows the binary map after we use scipy.ndimage.binary_fill_holes, to fill the holes, which correspond to areas inside bubbles, in the second column.