Returns an aperture mask creating using the thresholding method.
This method will identify the pixels in the TargetPixelFile which show
a median flux that is brighter than threshold times the standard
deviation above the overall median. The standard deviation is estimated
in a robust way by multiplying the Median Absolute Deviation (MAD)
If the thresholding method yields multiple contiguous regions, then
only the region closest to the (col, row) coordinate specified by
reference_pixel is returned. For exmaple, reference_pixel=(0, 0)
will pick the region closest to the bottom left corner.
By default, the region closest to the center of the mask will be
returned. If reference_pixel=None then all regions will be returned.
A value for the number of sigma by which a pixel needs to be
brighter than the median flux to be included in the aperture mask.
(col, row) pixel coordinate closest to the desired region.
For example, use reference_pixel=(0,0) to select the region
closest to the bottom left corner of the target pixel file.
If ‘center’ (default) then the region closest to the center pixel
will be selected. If None then all regions will be selected.
2D boolean numpy array containing True for pixels above the