determine_motion_target
====================================================

.. py:function:: petpal.preproc.motion_target.determine_motion_target(motion_target_option: str | tuple | list, input_image_path: str = None) -> str

   Produce a motion target given the ``motion_target_option`` from a method
   running registrations on PET, i.e. :meth:`motion_correction` or
   :meth:`register_pet`.

   The motion target option can be a string or a tuple. If it is a string,
   then if this string is a file, use the file as the motion target.

   If it is the option ``weighted_series_sum``, then run
   :meth:`weighted_series_sum` and return the output path.

   If it is the option ``mean_image``, then compute the time-average of the
   4D-PET image.

   If it is a tuple, run a weighted sum on the PET series on a range of
   frames. The elements of the tuple are treated as times in seconds, counted
   from the time of the first frame, i.e. (0,300) would average all frames
   from the first to the frame 300 seconds later. If the two elements are the
   same, returns the one frame closest to the entered time.

   :param motion_target_option: Determines how the method behaves,
                                according to the above description. Can be a file, a method
                                ('weighted_series_sum' or 'mean_image'), or a tuple range e.g. (0,600).
   :type motion_target_option: str | tuple | list
   :param input_image_path: Path to the PET image. This is intended to
                            be supplied by the parent method employing this function. Default
                            value None.
   :type input_image_path: str

   :returns: *out_image_file (str)* --

             File to use as a target to compute
                 transformations on.

   :raises ValueError: If ``motion_target_option`` is not a string, list, or tuple. If it is a string,
       but does not match one of the preset options or path to a file, the error will also be
       raised.
   :raises TypeError: If start and end time are incompatible with ``float`` type.