boxlist.py

import torch
from torchvision import ops


FLIP_LEFT_RIGHT = 0
FLIP_TOP_BOTTOM = 1

class BoxList(object):
    """
    This class represents a set of bounding boxes.
    The bounding boxes are represented as a Nx4 Tensor.
    In order to uniquely determine the bounding boxes with respect
    to an image, we also store the corresponding image dimensions.
    They can contain extra information that is specific to each bounding box, such as
    labels.
    """

    def __init__(self, bbox, image_size, mode="xyxy"):
        device = bbox.device if isinstance(bbox, torch.Tensor) else torch.device("cpu")
        bbox = torch.as_tensor(bbox, dtype=torch.float32, device=device)
        # if bbox.ndimension() != 2:
        #     raise ValueError(
        #         "bbox should have 2 dimensions, got {}".format(bbox.ndimension())
        #     )
        # if bbox.size(-1) != 4:
        #     raise ValueError(
        #         "last dimension of bbox should have a "
        #         "size of 4, got {}".format(bbox.size(-1))
        #     )
        if mode not in ("xyxy", "xywh"):
            raise ValueError("mode should be 'xyxy' or 'xywh'")

        self.bbox = bbox
        self.size = image_size  # (image_width, image_height)
        self.mode = mode
        self.extra_fields = {}

    def add_field(self, field, field_data):
        self.extra_fields[field] = field_data

    def get_field(self, field):
        return self.extra_fields[field]

    def has_field(self, field):
        return field in self.extra_fields

    def fields(self):
        return list(self.extra_fields.keys())

    def _copy_extra_fields(self, bbox):
        for k, v in bbox.extra_fields.items():
            self.extra_fields[k] = v

    def convert(self, mode):
        if mode not in ("xyxy", "xywh"):
            raise ValueError("mode should be 'xyxy' or 'xywh'")
        if mode == self.mode:
            return self
        # we only have two modes, so don't need to check
        # self.mode
        xmin, ymin, xmax, ymax = self._split_into_xyxy()
        if mode == "xyxy":
            bbox = torch.cat((xmin, ymin, xmax, ymax), dim=-1)
            bbox = BoxList(bbox, self.size, mode=mode)
        else:
            TO_REMOVE = 1
            bbox = torch.cat(
                (xmin, ymin, xmax - xmin + TO_REMOVE, ymax - ymin + TO_REMOVE), dim=-1
            )
            bbox = BoxList(bbox, self.size, mode=mode)
        bbox._copy_extra_fields(self)
        return bbox

    def _split_into_xyxy(self):
        if self.mode == "xyxy":
            xmin, ymin, xmax, ymax = self.bbox.split(1, dim=-1)
            return xmin, ymin, xmax, ymax
        elif self.mode == "xywh":
            TO_REMOVE = 1
            xmin, ymin, w, h = self.bbox.split(1, dim=-1)
            return (
                xmin,
                ymin,
                xmin + (w - TO_REMOVE).clamp(min=0),
                ymin + (h - TO_REMOVE).clamp(min=0),
            )
        else:
            raise RuntimeError("Should not be here")

    def resize(self, size, *args, **kwargs):
        """
        Returns a resized copy of this bounding box

        :param size: The requested size in pixels, as a 2-tuple:
            (width, height).
        """

        ratios = tuple(float(s) / float(s_orig) for s, s_orig in zip(size, self.size))
        if ratios[0] == ratios[1]:
            ratio = ratios[0]
            scaled_box = self.bbox * ratio
            bbox = BoxList(scaled_box, size, mode=self.mode)
            # bbox._copy_extra_fields(self)
            for k, v in self.extra_fields.items():
                if not isinstance(v, torch.Tensor):
                    v = v.resize(size, *args, **kwargs)
                bbox.add_field(k, v)
            return bbox

        ratio_width, ratio_height = ratios
        xmin, ymin, xmax, ymax = self._split_into_xyxy()
        scaled_xmin = xmin * ratio_width
        scaled_xmax = xmax * ratio_width
        scaled_ymin = ymin * ratio_height
        scaled_ymax = ymax * ratio_height
        scaled_box = torch.cat(
            (scaled_xmin, scaled_ymin, scaled_xmax, scaled_ymax), dim=-1
        )
        bbox = BoxList(scaled_box, size, mode="xyxy")
        # bbox._copy_extra_fields(self)
        for k, v in self.extra_fields.items():
            if not isinstance(v, torch.Tensor):
                v = v.resize(size, *args, **kwargs)
            bbox.add_field(k, v)

        return bbox.convert(self.mode)

    def transpose(self, method):
        """
        Transpose bounding box (flip or rotate in 90 degree steps)
        :param method: One of :py:attr:`PIL.Image.FLIP_LEFT_RIGHT`,
          :py:attr:`PIL.Image.FLIP_TOP_BOTTOM`, :py:attr:`PIL.Image.ROTATE_90`,
          :py:attr:`PIL.Image.ROTATE_180`, :py:attr:`PIL.Image.ROTATE_270`,
          :py:attr:`PIL.Image.TRANSPOSE` or :py:attr:`PIL.Image.TRANSVERSE`.
        """
        if method not in (FLIP_LEFT_RIGHT, FLIP_TOP_BOTTOM):
            raise NotImplementedError(
                "Only FLIP_LEFT_RIGHT and FLIP_TOP_BOTTOM implemented"
            )

        image_width, image_height = self.size
        xmin, ymin, xmax, ymax = self._split_into_xyxy()
        if method == FLIP_LEFT_RIGHT:
            TO_REMOVE = 1
            transposed_xmin = image_width - xmax - TO_REMOVE
            transposed_xmax = image_width - xmin - TO_REMOVE
            transposed_ymin = ymin
            transposed_ymax = ymax
        elif method == FLIP_TOP_BOTTOM:
            transposed_xmin = xmin
            transposed_xmax = xmax
            transposed_ymin = image_height - ymax
            transposed_ymax = image_height - ymin

        transposed_boxes = torch.cat(
            (transposed_xmin, transposed_ymin, transposed_xmax, transposed_ymax), dim=-1
        )
        bbox = BoxList(transposed_boxes, self.size, mode="xyxy")
        # bbox._copy_extra_fields(self)
        for k, v in self.extra_fields.items():
            if not isinstance(v, torch.Tensor):
                v = v.transpose(method)
            bbox.add_field(k, v)
        return bbox.convert(self.mode)

    def crop(self, box):
        """
        Cropss a rectangular region from this bounding box. The box is a
        4-tuple defining the left, upper, right, and lower pixel
        coordinate.
        """
        xmin, ymin, xmax, ymax = self._split_into_xyxy()
        w, h = box[2] - box[0], box[3] - box[1]
        cropped_xmin = (xmin - box[0]).clamp(min=0, max=w)
        cropped_ymin = (ymin - box[1]).clamp(min=0, max=h)
        cropped_xmax = (xmax - box[0]).clamp(min=0, max=w)
        cropped_ymax = (ymax - box[1]).clamp(min=0, max=h)

        # TODO should I filter empty boxes here?
        if False:
            is_empty = (cropped_xmin == cropped_xmax) | (cropped_ymin == cropped_ymax)

        cropped_box = torch.cat(
            (cropped_xmin, cropped_ymin, cropped_xmax, cropped_ymax), dim=-1
        )
        bbox = BoxList(cropped_box, (w, h), mode="xyxy")
        # bbox._copy_extra_fields(self)
        for k, v in self.extra_fields.items():
            if not isinstance(v, torch.Tensor):
                v = v.crop(box)
            bbox.add_field(k, v)
        return bbox.convert(self.mode)

    # Tensor-like methods

    def to(self, device):
        bbox = BoxList(self.bbox.to(device), self.size, self.mode)
        for k, v in self.extra_fields.items():
            if hasattr(v, "to"):
                v = v.to(device)
            bbox.add_field(k, v)
        return bbox

    def __getitem__(self, item):
        bbox = BoxList(self.bbox[item], self.size, self.mode)
        for k, v in self.extra_fields.items():
            bbox.add_field(k, v[item])
        return bbox

    def __len__(self):
        return self.bbox.shape[0]

    def clip_to_image(self, remove_empty=True):
        TO_REMOVE = 1
        self.bbox[:, 0].clamp_(min=0, max=self.size[0] - TO_REMOVE)
        self.bbox[:, 1].clamp_(min=0, max=self.size[1] - TO_REMOVE)
        self.bbox[:, 2].clamp_(min=0, max=self.size[0] - TO_REMOVE)
        self.bbox[:, 3].clamp_(min=0, max=self.size[1] - TO_REMOVE)
        if remove_empty:
            box = self.bbox
            keep = (box[:, 3] > box[:, 1]) & (box[:, 2] > box[:, 0])
            return self[keep]
        return self

    def area(self):
        box = self.bbox
        if self.mode == "xyxy":
            TO_REMOVE = 1
            area = (box[:, 2] - box[:, 0] + TO_REMOVE) * (box[:, 3] - box[:, 1] + TO_REMOVE)
        elif self.mode == "xywh":
            area = box[:, 2] * box[:, 3]
        else:
            raise RuntimeError("Should not be here")

        return area

    def box_span(self):
        box = self.bbox
        if self.mode == "xyxy":
            TO_REMOVE = 1
            span = torch.max((box[:, 2] - box[:, 0] + TO_REMOVE), (box[:, 3] - box[:, 1] + TO_REMOVE))
        elif self.mode == "xywh":
            span = torch.max(box[:, 2], box[:, 3])
        else:
            raise RuntimeError("Should not be here")

        return span

    def copy_with_fields(self, fields, skip_missing=False):
        bbox = BoxList(self.bbox, self.size, self.mode)
        if not isinstance(fields, (list, tuple)):
            fields = [fields]
        for field in fields:
            if self.has_field(field):
                bbox.add_field(field, self.get_field(field))
            elif not skip_missing:
                raise KeyError("Field '{}' not found in {}".format(field, self))
        return bbox

    def __repr__(self):
        s = self.__class__.__name__ + "("
        s += "num_boxes={}, ".format(len(self))
        s += "image_width={}, ".format(self.size[0])
        s += "image_height={}, ".format(self.size[1])
        s += "mode={})".format(self.mode)
        return s

def boxlist_nms(boxlist, nms_thresh, max_proposals=-1, score_field="scores"):
    """
    Performs non-maximum suppression on a boxlist, with scores specified
    in a boxlist field via score_field.

    Arguments:
        boxlist(BoxList)
        nms_thresh (float)
        max_proposals (int): if > 0, then only the top max_proposals are kept
            after non-maximum suppression
        score_field (str)
    """
    if nms_thresh <= 0:
        return boxlist
    mode = boxlist.mode
    boxlist = boxlist.convert("xyxy")
    boxes = boxlist.bbox
    score = boxlist.get_field(score_field)
    keep = ops.nms(boxes, score, nms_thresh)
    if max_proposals > 0:
        keep = keep[: max_proposals]
    boxlist = boxlist[keep]
    return boxlist.convert(mode)

def batched_nms(boxes, scores, idxs, iou_threshold):
    """
    Performs non-maximum suppression in a batched fashion.

    Each index value correspond to a category, and NMS
    will not be applied between elements of different categories.

    Parameters
    ----------
    boxes : Tensor[N, 4]
        boxes where NMS will be performed. They
        are expected to be in (x1, y1, x2, y2) format
    scores : Tensor[N]
        scores for each one of the boxes
    idxs : Tensor[N]
        indices of the categories for each one of the boxes.
    iou_threshold : float
        discards all overlapping boxes
        with IoU < iou_threshold

    Returns
    -------
    keep : Tensor
        int64 tensor with the indices of
        the elements that have been kept by NMS, sorted
        in decreasing order of scores
    """
    if boxes.numel() == 0:
        return torch.empty((0,), dtype=torch.int64, device=boxes.device)
    # strategy: in order to perform NMS independently per class.
    # we add an offset to all the boxes. The offset is dependent
    # only on the class idx, and is large enough so that boxes
    # from different classes do not overlap
    max_coordinate = boxes.max()
    offsets = idxs.to(boxes) * (max_coordinate + 1)
    boxes_for_nms = boxes + offsets[:, None]
    keep = ops.nms(boxes_for_nms, scores, iou_threshold)
    return keep

def boxlist_ml_nms(boxlist, nms_thresh, max_proposals=-1,
                   score_field="scores", label_field="labels"):
    """
    Performs non-maximum suppression on a boxlist, with scores specified
    in a boxlist field via score_field.

    Arguments:
        boxlist(BoxList)
        nms_thresh (float)
        max_proposals (int): if > 0, then only the top max_proposals are kept
            after non-maximum suppression
        score_field (str)
    """
    if nms_thresh <= 0:
        return boxlist
    mode = boxlist.mode
    boxlist = boxlist.convert("xyxy")
    boxes = boxlist.bbox
    scores = boxlist.get_field(score_field)
    labels = boxlist.get_field(label_field)
    keep = batched_nms(boxes, scores, labels.float(), nms_thresh)
    if max_proposals > 0:
        keep = keep[: max_proposals]
    boxlist = boxlist[keep]
    return boxlist.convert(mode)


def remove_small_boxes(boxlist, min_size):
    """
    Only keep boxes with both sides >= min_size

    Arguments:
        boxlist (Boxlist)
        min_size (int)
    """
    # TODO maybe add an API for querying the ws / hs
    xywh_boxes = boxlist.convert("xywh").bbox
    _, _, ws, hs = xywh_boxes.unbind(dim=1)
    keep = (
        (ws >= min_size) & (hs >= min_size)
    ).nonzero().squeeze(1)
    return boxlist[keep]


# implementation from https://github.com/kuangliu/torchcv/blob/master/torchcv/utils/box.py
# with slight modifications
def boxlist_iou(boxlist1, boxlist2):
    """Compute the intersection over union of two set of boxes.
    The box order must be (xmin, ymin, xmax, ymax).

    Arguments:
      box1: (BoxList) bounding boxes, sized [N,4].
      box2: (BoxList) bounding boxes, sized [M,4].

    Returns:
      (tensor) iou, sized [N,M].

    Reference:
      https://github.com/chainer/chainercv/blob/master/chainercv/utils/bbox/bbox_iou.py
    """
    if boxlist1.size != boxlist2.size:
        raise RuntimeError(
                "boxlists should have same image size, got {}, {}".format(boxlist1, boxlist2))

    N = len(boxlist1)
    M = len(boxlist2)

    area1 = boxlist1.area()
    area2 = boxlist2.area()

    box1, box2 = boxlist1.bbox, boxlist2.bbox

    lt = torch.max(box1[:, None, :2], box2[:, :2])  # [N,M,2]
    rb = torch.min(box1[:, None, 2:], box2[:, 2:])  # [N,M,2]

    TO_REMOVE = 1

    wh = (rb - lt + TO_REMOVE).clamp(min=0)  # [N,M,2]
    inter = wh[:, :, 0] * wh[:, :, 1]  # [N,M]

    iou = inter / (area1[:, None] + area2 - inter)
    return iou


# TODO redundant, remove
def _cat(tensors, dim=0):
    """
    Efficient version of torch.cat that avoids a copy if there is only a single element in a list
    """
    assert isinstance(tensors, (list, tuple))
    if len(tensors) == 1:
        return tensors[0]
    return torch.cat(tensors, dim)


def cat_boxlist(bboxes):
    """
    Concatenates a list of BoxList (having the same image size) into a
    single BoxList

    Arguments:
        bboxes (list[BoxList])
    """
    assert isinstance(bboxes, (list, tuple))
    assert all(isinstance(bbox, BoxList) for bbox in bboxes)

    size = bboxes[0].size
    assert all(bbox.size == size for bbox in bboxes)

    mode = bboxes[0].mode
    assert all(bbox.mode == mode for bbox in bboxes)

    fields = set(bboxes[0].fields())
    assert all(set(bbox.fields()) == fields for bbox in bboxes)

    cat_boxes = BoxList(_cat([bbox.bbox for bbox in bboxes], dim=0), size, mode)

    for field in fields:
        data = _cat([bbox.get_field(field) for bbox in bboxes], dim=0)
        cat_boxes.add_field(field, data)

    return cat_boxes