unu pad: Pad along each axis to make a bigger nrrd
Usage: unu pad -min <pos0 ...> -max <pos0 ...> [-b <behavior>] [-v <value>] \
[-i <nin>] [-o <nout>]
-min <pos0 ...> = low corner of bounding box.
o <int> gives 0-based index
o M, M+<int>, M-<int> give index relative to the last
sample on the axis (M == #samples-1).
(1 or more positions)
-max <pos0 ...> = high corner of bounding box. Besides the specification
styles described above, there's also:
o m+<int> give index relative to minimum.
(1 or more positions)
-b <behavior> = How to handle samples beyond the input bounds:
o "pad": use some specified value
o "bleed": extend border values outward
o "wrap": wrap-around to other side
default: "bleed"
-v <value> = for "pad" boundary behavior, pad with this value (double);
default: "0.0"
-i <nin> = input nrrd
-o <nout> = output nrrd (string); default: "-"
