python实现交并比IOU

    交并比（Intersection-over-Union，IoU），目标检测中使用的一个概念，是产生的候选框（candidate bound）与原标记框（ground truth bound）的交叠率，即它们的交集与并集的比值。最理想情况是完全重叠，即比值为1。

计算公式：

def cal_iou(box1, box2):
    """
    :param box1: = [xmin1, ymin1, xmax1, ymax1]
    :param box2: = [xmin2, ymin2, xmax2, ymax2]
    :return: 
    """
    xmin1, ymin1, xmax1, ymax1 = box1
    xmin2, ymin2, xmax2, ymax2 = box2
    # 计算每个矩形的面积
    s1 = (xmax1 - xmin1) * (ymax1 - ymin1)  # C的面积
    s2 = (xmax2 - xmin2) * (ymax2 - ymin2)  # G的面积

    # 计算相交矩形
    xmin = max(xmin1, xmin2)
    ymin = max(ymin1, ymin2)
    xmax = min(xmax1, xmax2)
    ymax = min(ymax1, ymax2)

    w = max(0, xmax - xmin)
    h = max(0, ymax - ymin)
    area = w * h  # C∩G的面积
    iou = area / (s1 + s2 - area)
    return iou      

# -*-coding: utf-8 -*-
"""
    @Project: IOU
    @File   : IOU.py
    @Author : panjq
    @E-mail : [email protected]
    @Date   : 2018-10-14 10:44:06
"""
def calIOU_V1(rec1, rec2):
    """
    computing IoU
    :param rec1: (y0, x0, y1, x1), which reflects
            (top, left, bottom, right)
    :param rec2: (y0, x0, y1, x1)
    :return: scala value of IoU
    """
    # 计算每个矩形的面积
    S_rec1 = (rec1[2] - rec1[0]) * (rec1[3] - rec1[1])
    S_rec2 = (rec2[2] - rec2[0]) * (rec2[3] - rec2[1])

    # computing the sum_area
    sum_area = S_rec1 + S_rec2

    # find the each edge of intersect rectangle
    left_line = max(rec1[1], rec2[1])
    right_line = min(rec1[3], rec2[3])
    top_line = max(rec1[0], rec2[0])
    bottom_line = min(rec1[2], rec2[2])

    # judge if there is an intersect
    if left_line >= right_line or top_line >= bottom_line:
        return 0
    else:
        intersect = (right_line - left_line) * (bottom_line - top_line)
        return intersect/(sum_area - intersect)

def calIOU_V2(rec1, rec2):
    """
    computing IoU
    :param rec1: (y0, x0, y1, x1), which reflects
            (top, left, bottom, right)
    :param rec2: (y0, x0, y1, x1)
    :return: scala value of IoU
    """
    # cx1 = rec1[0]
    # cy1 = rec1[1]
    # cx2 = rec1[2]
    # cy2 = rec1[3]
    # gx1 = rec2[0]
    # gy1 = rec2[1]
    # gx2 = rec2[2]
    # gy2 = rec2[3]
    cx1,cy1,cx2,cy2=rec1
    gx1,gy1,gx2,gy2=rec2
    # 计算每个矩形的面积
    S_rec1 = (cx2 - cx1) * (cy2 - cy1)  # C的面积
    S_rec2 = (gx2 - gx1) * (gy2 - gy1)  # G的面积

    # 计算相交矩形
    x1 = max(cx1, gx1)
    y1 = max(cy1, gy1)
    x2 = min(cx2, gx2)
    y2 = min(cy2, gy2)

    w = max(0, x2 - x1)
    h = max(0, y2 - y1)
    area = w * h  # C∩G的面积

    iou = area / (S_rec1 + S_rec2 - area)
    return iou

if __name__=='__main__':
    rect1 = (661, 27, 679, 47)
    # (top, left, bottom, right)
    rect2 = (662, 27, 682, 47)
    iou1 = calIOU_V1(rect1, rect2)
    iou2 = calIOU_V2(rect1, rect2)
    print(iou1)
    print(iou2)