def add_data_annotation(self):
        """Add text to display values of grayscale data"""
        if self._data_annotation is not None:
            raise ValueError("data annotation already added")

        if self.data.value.ndim > 2:
            raise ValueError("image data annotation only supported for grayscale data")

        self._data_annotation = pygfx.MultiText(
            screen_space=True,
            font_size=12,
            material=pygfx.TextMaterial(color="w", outline_thickness=0.1)
        )

        self._text_blocks = np.empty(shape=self.data.value.shape, dtype=object)

        for (row_ix, col_ix) in product(range(self.data.value.shape[0]), range(self.data.value.shape[1])):
            self._text_blocks[row_ix, col_ix] = self._data_annotation.create_text_block()
            self._text_blocks[row_ix, col_ix].set_text(str(self.data[row_ix, col_ix]))
            self._text_blocks[row_ix, col_ix].set_position(col_ix, row_ix)

        self._data_annotation.local.z = self.offset[-1] + 1

        self.world_object.add(self._data_annotation)

        # self.add_event_handler(self._update_data_annotation, "data")

        return self._data_annotation

    def update_data_annotation(self, ev):
        for (row_ix, col_ix) in product(range(self.data.value.shape[0]), range(self.data.value.shape[1])):
            self._text_blocks[row_ix, col_ix].set_text(str(self.data[row_ix, col_ix]))