def compute_bbox_regression_targets(entry):
    """Compute bounding-box regression targets for an image."""
    # Indices of ground-truth ROIs
    rois = entry['boxes']
    overlaps = entry['max_overlaps']
    labels = entry['max_classes']
    gt_inds = np.where((entry['gt_classes'] > 0) & (entry['is_crowd'] == 0))[0]
    # Targets has format (class, tx, ty, tw, th)
    targets = np.zeros((rois.shape[0], 5), dtype=np.float32)
    if len(gt_inds) == 0:
        # Bail if the image has no ground-truth ROIs
        return targets

    # Indices of examples for which we try to make predictions
    ex_inds = np.where(overlaps >= cfg.TRAIN.BBOX_THRESH)[0]

    # Get IoU overlap between each ex ROI and gt ROI
    ex_gt_overlaps = box_utils.bbox_overlaps(
        rois[ex_inds, :].astype(dtype=np.float32, copy=False),
        rois[gt_inds, :].astype(dtype=np.float32, copy=False))

    # Find which gt ROI each ex ROI has max overlap with:
    # this will be the ex ROI's gt target
    gt_assignment = ex_gt_overlaps.argmax(axis=1)
    gt_rois = rois[gt_inds[gt_assignment], :]
    ex_rois = rois[ex_inds, :]
    # Use class "1" for all boxes if using class_agnostic_bbox_reg
    targets[ex_inds, 0] = (
        1 if cfg.MODEL.CLS_AGNOSTIC_BBOX_REG else labels[ex_inds])
    targets[ex_inds, 1:] = box_utils.bbox_transform_inv(
        ex_rois, gt_rois, cfg.MODEL.BBOX_REG_WEIGHTS)
    return targets
Compute bounding-box regression targets for an image.
detectron/datasets/roidb.py