code: def cut_psf(psf_data, psf_size):
      
      kernel = image_util.cut_edges(psf_data, psf_size)
      kernel = kernel_norm(kernel)
      return kernel
docs: cut the psf properly
      :param psf_data: image of PSF
      :param psf_size: size of psf
      :return: re-sized and re-normalized PSF