afni.nimh.nih.gov

Hi
I am trying to run
====
set path_P_ss = data_proc/SUBJ_001

fat_proc_select_vols \
-in_dwi $path_P_ss/dwi_00/ap.nii.gz \
-in_img $path_P_ss/dwi_00/ap_sepscl.sag.png \
-prefix $path_P_ss/dwi_01/dwi_sel_ap
====
However, i only have nii for dti, not dcm files. So i did not run dcm to nii, then no png for this command. Is there any command that i can generate this png using nii file?
thanks.
rujing