def init_slab(self, slab=None, segmentation=None, voxelsize_mm=None, show_ok_button=False):
        """
        Create widget with segmentation labels information used to select labels.

        :param slab: dict with label name and its id
        :param segmentation: 3D label ndarray
        :param voxelsize_mm: size of voxel in mm
        :return:
        """
        self.segmentation = segmentation
        self.voxelsize_mm = voxelsize_mm

        from . import show_segmentation
        self.slab = show_segmentation.create_slab_from_segmentation(
            self.segmentation, slab=slab)

        if show_ok_button:
            ok_button = QPushButton("Ok")
            ok_button.clicked.connect(self._action_ok_button)

            self.superMainScrollLayout.addWidget(ok_button)