FIX: Ensure anat image is Nifti

Author: mgxd

niworkflows/viz/utils.py

@@ -341,6 +341,8 @@ def plot_registration(
     if cuts is None:
         raise NotImplementedError  # TODO
 
+    anat_nii = _ensure_nii(anat_nii)
+
     out_files = []
     if estimate_brightness:
         plot_params = robust_set_limits(anat_nii.get_fdata().reshape(-1), plot_params)
@@ -714,3 +716,9 @@ def plot_melodic_components(
         pad_inches=0.01,
     )
     fig.clf()
+
+
+def _ensure_nii(img: nb.spatialimages.SpatialImage) -> nb.Nifti1Image:
+    if not isinstance(img, nb.Nifti1Image):
+        img = nb.Nifti1Image(img.dataobj, img.affine, img.header)
+    return img