Hi Jan,
The niml.dset format is not necessarily intended to be read by
the human eye, any more than a BRIK file is. You can write them
in text format by setting AFNI_NIML_TEXT_DATA to YES, but that
negates the speed benefit of using the binary niml format.
Perhaps you should write out one with AFNI_NIML_TEXT_DATA set to
YES (just so you can read the output), but then do the rest with
it unset, or set to NO.
- rick