code: def read_talxfm(subject, subjects_dir=None, verbose=None):
      """Compute MRI-to-MNI transform from FreeSurfer talairach.xfm file.
  
      Parameters
      ----------
      %(subject)s
      %(subjects_dir)s
      %(verbose)s
  
      Returns
      -------
      mri_mni_t : instance of Transform
          The affine transformation from MRI to MNI space for the subject.
      """
      # Adapted from freesurfer m-files. Altered to deal with Norig
      # and Torig correctly
      subjects_dir = get_subjects_dir(subjects_dir)
      # Setup the RAS to MNI transform
      ras_mni_t = read_ras_mni_t(subject, subjects_dir)
      ras_mni_t["trans"][:3, 3] /= 1000.0  # mm->m
  
      # We want to get from Freesurfer surface RAS ('mri') to MNI ('mni_tal').
      # This file only gives us RAS (non-zero origin) ('ras') to MNI ('mni_tal').
      # Se we need to get the ras->mri transform from the MRI headers.
  
      # To do this, we get Norig and Torig
      # (i.e. vox_ras_t and vox_mri_t, respectively)
      path = subjects_dir / subject / "mri" / "orig.mgz"
      if not path.is_file():
          path = subjects_dir / subject / "mri" / "T1.mgz"
      if not path.is_file():
          raise OSError("mri not found: %s" % path)
      _, _, mri_ras_t, _, _ = _read_mri_info(path)
      mri_mni_t = combine_transforms(
          mri_ras_t, ras_mni_t, "mri", "mni_tal"
      )
      return mri_mni_t
  
imports: import os.path
  from gzip import GzipFile
  from pathlib import Path
  import numpy
  from ._fiff.constants import FIFF
  from ._fiff.meas_info import read_fiducials
  from .surface import _read_mri_surface, read_surface
  from .transforms import Transform, _ensure_trans, apply_trans, combine_transforms, invert_transform, read_ras_mni_t
  from .utils import _check_fname, _check_option, _import_nibabel, _validate_type, get_subjects_dir, logger, verbose
label_desc: Use image node_id 17 for calling a global function with example usage: read_talxfm(subject, subjects_dir, verbose) and returns: mri_mni_t