Hello QIn, These numbers refer to the atlas image itself - HarvardOxford-sub-prob-2mm.nii.gz. The index is the volume index of the 4D file. Kind Regards Matthew > Dear FSLexperts, > I have a problem about the HavardOxford-Subcortical.xlm. I found the index in this file was not consistent with the intensity in the $FSLDIR/data/atlases/HavardOxford/HavardOxford-Sub-maxprob-thr25-1mm.nii.gz. For example, for > label 'index="0", x="58", y="37", z="50" which indicates left Cerebral White Matter, the intensity of the same voxel coordinates in HavardOxford-Sub-maxprob-thr25-1mm.nii.gz is "1". It seems that the intensities are always 1 bigger than the label indice. > Is there something wrong with the HavardOxford-Subcortical.xlm, or I misunderstood something? > Thanks for the comment. > Best, > Qin >