【Detectron2】代码库学习-5.标注格式- 矩形框， 旋转框，关键点， mask， 实例标注，IOU计算， 旋转框IOU计算，

Detectron2 内置的标注格式

• Boxes
• RotatedBoxes
• BitMasks
• PolygonMasks
• ROIMasks
• Keypoints
• Instances
• ImageList

BoxMode 表示方式

• XYXY_ABS
• XYWH_ABS
• XYXY_REL # 相对模式
• XYWH_REL # 相对模式
• XYWHA_ABS # 带角度的旋转框 xc, yc 中心点坐标； A， 逆时针度数

实用API

成对Boxes 交集计算

def pairwise_intersection(boxes1: Boxes, boxes2: Boxes) -> torch.Tensor:
    """
    Given two lists of boxes of size N and M,
    compute the intersection area between __all__ N x M pairs of boxes.
    The box order must be (xmin, ymin, xmax, ymax)

    Args:
        boxes1,boxes2 (Boxes): two `Boxes`. Contains N & M boxes, respectively.

    Returns:
        Tensor: intersection, sized [N,M].
    """
    boxes1, boxes2 = boxes1.tensor, boxes2.tensor
    width_height = torch.min(boxes1[:, None, 2:], boxes2[:, 2:]) - torch.max(
        boxes1[:, None, :2], boxes2[:, :2]
    )  # [N,M,2]

    width_height.clamp_(min=0)  # [N,M,2]
    intersection = width_height.prod(dim=2)  # [N,M]
    return intersection
    ```

成对Boxes IOU 计算
```python
def pairwise_iou(boxes1: Boxes, boxes2: Boxes) -> torch.Tensor:
    """
    Given two lists of boxes of size N and M, compute the IoU
    (intersection over union) between **all** N x M pairs of boxes.
    The box order must be (xmin, ymin, xmax, ymax).

    Args:
        boxes1,boxes2 (Boxes): two `Boxes`. Contains N & M boxes, respectively.

    Returns:
        Tensor: IoU, sized [N,M].
    """
    area1 = boxes1.area()  # [N]
    area2 = boxes2.area()  # [M]
    inter = pairwise_intersection(boxes1, boxes2)

    # handle empty boxes
    iou = torch.where(
        inter > 0,
        inter / (area1[:, None] + area2 - inter),
        torch.zeros(1, dtype=inter.dtype, device=inter.device),
    )
    return iou
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RotatedBoxes

旋转框 表示 N x 5， N个 框， cx, cy, w,h, angle 。 旋转框角度 无范围限制， 推荐 在 [-180, 180)
旋转角表示法：

def inside_box(self, box_size: Tuple[int, int], boundary_threshold: int = 0) -> torch.Tensor:
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支持旋转框尺度放缩，

    def scale(self, scale_x: float, scale_y: float) -> None:
        """
        Scale the rotated box with horizontal and vertical scaling factors
        Note: when scale_factor_x != scale_factor_y,
        the rotated box does not preserve the rectangular shape when the angle
        is not a multiple of 90 degrees under resize transformation.
        Instead, the shape is a parallelogram (that has skew)
        Here we make an approximation by fitting a rotated rectangle to the parallelogram.
        """
        self.tensor[:, 0] *= scale_x
        self.tensor[:, 1] *= scale_y
        theta = self.tensor[:, 4] * math.pi / 180.0
        c = torch.cos(theta)
        s = torch.sin(theta)

        # In image space, y is top->down and x is left->right
        # Consider the local coordintate system for the rotated box,
        # where the box center is located at (0, 0), and the four vertices ABCD are
        # A(-w / 2, -h / 2), B(w / 2, -h / 2), C(w / 2, h / 2), D(-w / 2, h / 2)
        # the midpoint of the left edge AD of the rotated box E is:
        # E = (A+D)/2 = (-w / 2, 0)
        # the midpoint of the top edge AB of the rotated box F is:
        # F(0, -h / 2)
        # To get the old coordinates in the global system, apply the rotation transformation
        # (Note: the right-handed coordinate system for image space is yOx):
        # (old_x, old_y) = (s * y + c * x, c * y - s * x)
        # E(old) = (s * 0 + c * (-w/2), c * 0 - s * (-w/2)) = (-c * w / 2, s * w / 2)
        # F(old) = (s * (-h / 2) + c * 0, c * (-h / 2) - s * 0) = (-s * h / 2, -c * h / 2)
        # After applying the scaling factor (sfx, sfy):
        # E(new) = (-sfx * c * w / 2, sfy * s * w / 2)
        # F(new) = (-sfx * s * h / 2, -sfy * c * h / 2)
        # The new width after scaling tranformation becomes:

        # w(new) = |E(new) - O| * 2
        #        = sqrt[(sfx * c * w / 2)^2 + (sfy * s * w / 2)^2] * 2
        #        = sqrt[(sfx * c)^2 + (sfy * s)^2] * w
        # i.e., scale_factor_w = sqrt[(sfx * c)^2 + (sfy * s)^2]
        #
        # For example,
        # when angle = 0 or 180, |c| = 1, s = 0, scale_factor_w == scale_factor_x;
        # when |angle| = 90, c = 0, |s| = 1, scale_factor_w == scale_factor_y
        self.tensor[:, 2] *= torch.sqrt((scale_x * c) ** 2 + (scale_y * s) ** 2)

        # h(new) = |F(new) - O| * 2
        #        = sqrt[(sfx * s * h / 2)^2 + (sfy * c * h / 2)^2] * 2
        #        = sqrt[(sfx * s)^2 + (sfy * c)^2] * h
        # i.e., scale_factor_h = sqrt[(sfx * s)^2 + (sfy * c)^2]
        #
        # For example,
        # when angle = 0 or 180, |c| = 1, s = 0, scale_factor_h == scale_factor_y;
        # when |angle| = 90, c = 0, |s| = 1, scale_factor_h == scale_factor_x
        self.tensor[:, 3] *= torch.sqrt((scale_x * s) ** 2 + (scale_y * c) ** 2)

        # The angle is the rotation angle from y-axis in image space to the height
        # vector (top->down in the box's local coordinate system) of the box in CCW.
        #
        # angle(new) = angle_yOx(O - F(new))
        #            = angle_yOx( (sfx * s * h / 2, sfy * c * h / 2) )
        #            = atan2(sfx * s * h / 2, sfy * c * h / 2)
        #            = atan2(sfx * s, sfy * c)
        #
        # For example,
        # when sfx == sfy, angle(new) == atan2(s, c) == angle(old)
        self.tensor[:, 4] = torch.atan2(scale_x * s, scale_y * c) * 180 / math.pi
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支持计算成对旋转框 IOU 计算，

def pairwise_iou(boxes1: RotatedBoxes, boxes2: RotatedBoxes) -> None:
    """
    Given two lists of rotated boxes of size N and M,
    compute the IoU (intersection over union)
    between **all** N x M pairs of boxes.
    The box order must be (x_center, y_center, width, height, angle).

    Args:
        boxes1, boxes2 (RotatedBoxes):
            two `RotatedBoxes`. Contains N & M rotated boxes, respectively.

    Returns:
        Tensor: IoU, sized [N,M].
    """
    return pairwise_iou_rotated(boxes1.tensor, boxes2.tensor)

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Instances 实例标注

Instances数据结构包含一个图像的所有实例，如Boxes， Masks,可通过域操作设置和获取值。所有属性对应的实例数量许保持一致。

instances=Instances((640,640), ...) 
instances.gt_boxes= Boxes(...)
pred_boxes=instances.pred_masks
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可以通过python 语法判断是否包含特定结果。

assert "gt_mask" in instances
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可以通过len获取实例个数

print(len(instances))
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可以通过 index 获取特定实例

# 获取得分大于0.9 的 实例
confident_detections = instances[instances.scores > 0.9]

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Keypoints

存储关键点标注数据，

gt_points= keypoints.gt_keypoints # (N, K，3)
# N 个实例，每个实例K 个点， 每个点  x,y, visible
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可将 keypoint 转为 方形heatmap 格式。

heatmaps= keypoints.to_heatmap(boxes, heatmap_size)
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可将预测heatmap 转换为 keypoint 格式

Masks

通过COCO API 将多边形转为 Masks

def polygons_to_bitmask(polygons: List[np.ndarray], height: int, width: int) -> np.ndarray:
    """
    Args:
        polygons (list[ndarray]): each array has shape (Nx2,)
        height, width (int)

    Returns:
        ndarray: a bool mask of shape (height, width)
    """
    if len(polygons) == 0:
        # COCOAPI does not support empty polygons
        return np.zeros((height, width)).astype(np.bool)
    rles = mask_util.frPyObjects(polygons, height, width)
    rle = mask_util.merge(rles)
    return mask_util.decode(rle).astype(np.bool)
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BitMasks 标注

PolygonMasks

ROI Masks

均支持 get_bounding box 和 计算面积。

结语

detectron2 提供了多种标注类型的标准数据结构和丰富多样的API， 方便直接使用或者在其他项目中使用。