def add_ResNet_roi_conv5_head_for_masks(model, blob_in, dim_in, spatial_scale):
    """Add a ResNet "conv5" / "stage5" head for predicting masks."""
    model.RoIFeatureTransform(
        blob_in,
        blob_out='_[mask]_pool5',
        blob_rois='mask_rois',
        method=cfg.MRCNN.ROI_XFORM_METHOD,
        resolution=cfg.MRCNN.ROI_XFORM_RESOLUTION,
        sampling_ratio=cfg.MRCNN.ROI_XFORM_SAMPLING_RATIO,
        spatial_scale=spatial_scale
    )

    dilation = cfg.MRCNN.DILATION
    stride_init = int(cfg.MRCNN.ROI_XFORM_RESOLUTION / 7)  # by default: 2

    s, dim_in = ResNet.add_stage(
        model,
        '_[mask]_res5',
        '_[mask]_pool5',
        3,
        dim_in,
        2048,
        512,
        dilation,
        stride_init=stride_init
    )

    return s, 2048
Add a ResNet "conv5" / "stage5" head for predicting masks.
detectron/modeling/mask_rcnn_heads.py