Hi Tournier,
Thank you so much for your explanation. I put directions.mif, index.mif and peak_amplitude.mif together in the same folder ‘test’ and ran the command again:
fixel2sh test/amp.mif WM_FODs_restore.mif
and found that WM_FODs_restore.mif was generated successfully.
Original WM FODs
The restored FODs.
We can see that the size of each FOD voxel in the restored FOD image is little bit larger than that in the original one. This can be also reflected from the value of the first order of these FODs. It is very weird. Also, another question comes up. How can the fixel2sh restore a FOD image only using direction and amplitude information (I only used index.mif, directions.mif, and peak_amplitude.mif). I think the amplitude information has a lot of ambiguity since two totally different FODs may have same amplitude but different dispersion as mentioned by The difference of FOD - MRtrix3 Community
Many thanks!
Best regards,
Rui Zeng