Controls how multiple COM masks are combined
"com.zero_lowhits" and
parameter "com.zero_snr" ), then they are combined into a single mask. If com.zero_union is true (i.e.
non-zero), then the source region in the combined mask is the union of the source regions in the individual
masks. If com.zero_union is false (i.e. zero), then the source region in the combined mask is the intersection of
the source regions in the individual masks. [1]