Provides alternative method for SNR masking
"com.zero_snr" to be created using an algorithm like that used by the KAPPA command " FFCLEAN"
(see SUN/95), instead of using a simple thresholding of the SNR map. The parameter "com.zero_snr"
gives the clipping level of the ffclean algorithm, and the parameter "com.zero_snr_hipass"
gives the box size. Using an ffclean algorithm prevents the source regions within the mask
being larger than the box size. [0]