add a comment regarding datatype support

bthyreau · bthyreau · commit e03cacc26dfa · 2025-05-16T11:07:41.000+09:00
diff --git a/nibabel/freesurfer/mghformat.py b/nibabel/freesurfer/mghformat.py
@@ -57,6 +57,10 @@
 
 # caveat: Note that it's ambiguous to get the code given the bytespervoxel
 # caveat 2: Note that the bytespervox you get is in str ( not an int)
+# FreeSurfer historically defines codes 0-10 [1], but only a subset is well supported.
+# Here we use FreeSurfer's MATLAB loader [2] as an indication of current support.
+# [1] https://github.com/freesurfer/freesurfer/blob/v8.0.0/include/mri.h#L53-L63
+# [2] https://github.com/freesurfer/freesurfer/blob/v8.0.0/matlab/load_mgh.m#L195-L207
 _dtdefs = (  # code, conversion function, dtype, bytes per voxel
     (0, 'uint8', '>u1', '1', 'MRI_UCHAR', np.uint8, np.dtype('u1'), np.dtype('>u1')),
     (1, 'int32', '>i4', '4', 'MRI_INT', np.int32, np.dtype('i4'), np.dtype('>i4')),
