Return background-corrected QPImage of data at index `idx`

def get_qpimage(self, idx):
        """Return background-corrected QPImage of data at index `idx`"""
        if self._bgdata:
            # The user has explicitly chosen different background data
            # using `get_qpimage_raw`.
            qpi = super(SeriesHdf5Qpimage, self).get_qpimage(idx)
        else:
            # We can use the background data stored in the qpimage hdf5 file
            with self._qpseries() as qps:
                qpi = qps.get_qpimage(index=idx).copy()
            # Force meta data
            for key in self.meta_data:
                qpi[key] = self.meta_data[key]
            # set identifier
            qpi["identifier"] = self.get_identifier(idx)
        return qpi