fScan Reference Manual, Chapter 2 (CmdLineOptions:Expr): erode
usage: -expr [NREPTS] [static] erode val maskbits newval flag nmatch nneighbors
VAL - “Inside” value (or Percent value if (FLAG & (4|8))
MASKBITS - voxel data values to consider for comparing with VAL (DATABITS is inverse of MASKBITS)
NEWVAL - bit-value to turn on when adding (dilating) a voxel. If NEWVAL is negative and MASKBITS is zero, then the input data voxel value will be used when dilating into neighboring voxels.