afni.nimh.nih.gov

Hello,

Please go ahead and try it. AFNI programs read .nii and .nii.gz
files as they are specified. You should not have to do anything
with the files.

Though note, to compress (.nii -> .nii.gz), one could use gzip.
In the other direction, one could use gzip -d or gunzip. Also,
AFNI programs will write .nii or .nii.gz as specified in the output
name.

But again, you should not need to alter the compression.

- rick