facebookresearch/detectron2 · error · ValueError

Failed to use mask_format=='polygon' from the given annotati

Error message

Failed to use mask_format=='polygon' from the given annotations!

What it means

Error "Failed to use mask_format=='polygon' from the given annotations!" thrown in facebookresearch/detectron2.

Source

Thrown at detectron2/data/detection_utils.py:421

            [BoxMode.convert(obj["bbox"], obj["bbox_mode"], BoxMode.XYXY_ABS) for obj in annos]
        )
        if len(annos)
        else np.zeros((0, 4))
    )
    target = Instances(image_size)
    target.gt_boxes = Boxes(boxes)

    classes = [int(obj["category_id"]) for obj in annos]
    classes = torch.tensor(classes, dtype=torch.int64)
    target.gt_classes = classes

    if len(annos) and "segmentation" in annos[0]:
        segms = [obj["segmentation"] for obj in annos]
        if mask_format == "polygon":
            try:
                masks = PolygonMasks(segms)
            except ValueError as e:
                raise ValueError(
                    "Failed to use mask_format=='polygon' from the given annotations!"
                ) from e
        else:
            assert mask_format == "bitmask", mask_format
            masks = []
            for segm in segms:
                if isinstance(segm, list):
                    # polygon
                    masks.append(polygons_to_bitmask(segm, *image_size))
                elif isinstance(segm, dict):
                    # COCO RLE
                    masks.append(mask_util.decode(segm))
                elif isinstance(segm, np.ndarray):
                    assert segm.ndim == 2, "Expect segmentation of 2 dimensions, got {}.".format(
                        segm.ndim
                    )
                    # mask array
                    masks.append(segm)

View on GitHub (pinned to a2f4a8771a)

When it happens

Trigger: Thrown at detectron2/data/detection_utils.py:421 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of facebookresearch/detectron2@a2f4a8771a (2026-08-27). Data as JSON: /api/errors/76e6864958a20f27. Report an issue: GitHub.