gen_3d_img_from_timeseries
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.. py:function:: petpal.utils.dimension.gen_3d_img_from_timeseries(input_img: ants.ANTsImage) -> ants.ANTsImage

   Get the first frame of a 4D image as a template 3D image with voxel value zero.

   A simplified version of :py:func:`ants.ndimage_to_list.ndimage_to_list`.

   :param input_img: The 4D image from which to get the template image.
   :type input_img: ants.ANTsImage

   :returns: *img_3d (ants.ANTsImage)* -- The 3D template of the input image as an ants image.