matched
            with a predicted segment.
        pred_areas: Mapping from colors of the predicted segments to their extents.
        target_areas: Mapping from colors of the ground truth segments to their extents.
        intersection_areas: Mapping from tuples of `(pred_color, target_color)` to their extent.
        void_color: An additional color that is masked out during metrics calculation.

    Returns:
        The calculated IoU as a torch.Tensor containing a single scalar value.

    r