apply_xfm_fsl
=====================================

.. py:function:: petpal.preproc.register.apply_xfm_fsl(input_image_path: str, ref_image_path: str, out_image_path: str, warp_path: str = None, premat_path: str = '', postmat_path: str = '', **kwargs)

   Applies existing transforms in FSL format to an input image, onto a
   reference image. This is useful for applying the same transform on
   different images to atlas space, for example.

   .. important::
       Requires installation of ``FSL``, and environment variables ``FSLDIR`` and
       ``FSLOUTPUTTYPE`` set appropriately in the shell.

   :param input_image_path: Path to image on which transform is applied.
   :type input_image_path: str
   :param ref_image_path: Path to image to which transform is applied.
   :type ref_image_path: str
   :param out_image_path: Path to which the transformed image is saved.
   :type out_image_path: str
   :param warp_path: Path to FSL warp file.
   :type warp_path: str
   :param premat_path: Path to FSL ``premat`` matrix file.
   :type premat_path: str
   :param postmat_path: Path to FSL ``postmat`` matrix file.
   :type postmat_path: str
   :param kwargs: Additional arguments passed to
                  :py:func:`fsl.wrappers.applywarp`.
   :type kwargs: keyword arguments