docs: def get_qpimage_raw(self, idx=0):
          """Return QPImage without background correction"""
          name = self._get_experiments()[idx]
          with h5py.File(name=self.path, mode="r") as h5:
              exp = h5["Experiments"][name]
              # hologram data
              data = exp["data"][:]
              # resolution
              rx = exp["axis-0"].attrs["scale"]
              ry = exp["axis-1"].attrs["scale"]
              if rx != ry:
                  raise NotImplementedError("Only square pixels supported!")
              runit = exp["axis-0"].attrs["units"]
              if runit == "nm":
                  pixel_size = rx * 1e-9
              else:
                  raise NotImplementedError("Units '{}' not implemented!")
  
          meta_data = {"pixel size": pixel_size}
          meta_data.update(self.meta_data)
  
          qpi = qpimage.QPImage(data=data,
                                which_data="hologram",
                                meta_data=meta_data,
                                holo_kw=self.holo_kw,
                                h5dtype=self.as_type)
          # set identifier
          qpi["identifier"] = self.get_identifier(idx)
          return qpi