Generate test 3D volume of integers. The volume has an outer background area (intensity value 'bg') and an inner foreground areas (intensity value 200L).
gen.test.volume(vdim = c(256L, 256L, 256L), bg = NA)
integer vector of length 3, the dimensions
value to use for outer background voxels. Typically `0L` or `NA`.
a 3d array of integers