def select_foreground_proposals(
    proposals: List[Instances], bg_label: int
) -> Tuple[List[Instances], List[torch.Tensor]]:
    """
    Given a list of N Instances (for N images), each containing a `gt_classes` field,
    return a list of Instances that contain only instances with `gt_classes != -1 &&
    gt_classes != bg_label`.

    Args:
        proposals (list[Instances]): A list of N Instances, where N is the number of
            images in the batch.
        bg_label: label index of background class.

    Returns:
        list[Instances]: N Instances, each contains only the selected foreground instances.
        list[Tensor]: N boolean vector, correspond to the selection mask of
            each Instances object. True for selected instances.
    """
    assert isinstance(proposals, (list, tuple))
    assert isinstance(proposals[0], Instances)
    assert proposals[0].has("gt_classes")
    fg_proposals = []
    fg_selection_masks = []
    for proposals_per_image in proposals:
        gt_classes = proposals_per_image.gt_classes
        fg_selection_mask = (gt_classes != -1) & (gt_classes != bg_label)
        fg_idxs = fg_selection_mask.nonzero().squeeze(1)
        fg_proposals.append(proposals_per_image[fg_idxs])
        fg_selection_masks.append(fg_selection_mask)
    return fg_proposals, fg_selection_masks

    Given a list of N Instances (for N images), each containing a `gt_classes` field,
    return a list of Instances that contain only instances with `gt_classes != -1 &&
    gt_classes != bg_label`.

    Args:
        proposals (list[Instances]): A list of N Instances, where N is the number of
            images in the batch.
        bg_label: label index of background class.

    Returns:
        list[Instances]: N Instances, each contains only the selected foreground instances.
        list[Tensor]: N boolean vector, correspond to the selection mask of
            each Instances object. True for selected instances.
    
video_chat_text/video_chat_with_StableLM/models/grit_src/third_party/CenterNet2/detectron2/modeling/roi_heads/roi_heads.py