假设两个矩形框A和B的位置分别为：
如果二者有相交部分，则相交部分左上角坐标为：
相交部分右下角坐标为：
计算先交部分面积：
矩形框A和B的面积分别是：
计算相并部分面积：
计算交并比：
# 计算IoU，矩形框的坐标形式为xyxy，这个函数会被保存在box_utils.py文件中
def box_iou_xyxy(box1, box2):
# 获取box1左上角和右下角的坐标
x1min, y1min, x1max, y1max = box1[0], box1[1], box1[2], box1[3]
# 计算box1的面积
s1 = (y1max - y1min + 1.) * (x1max - x1min + 1.)
# 获取box2左上角和右下角的坐标
x2min, y2min, x2max, y2max = box2[0], box2[1], box2[2], box2[3]
# 计算box2的面积
s2 = (y2max - y2min + 1.) * (x2max - x2min + 1.)
# 计算相交矩形框的坐标
xmin = np.maximum(x1min, x2min)
ymin = np.maximum(y1min, y2min)
xmax = np.minimum(x1max, x2max)
ymax = np.minimum(y1max, y2max)
# 计算相交矩形行的高度、宽度、面积
inter_h = np.maximum(ymax - ymin + 1., 0.)
inter_w = np.maximum(xmax - xmin + 1., 0.)
intersection = inter_h * inter_w
# 计算相并面积
union = s1 + s2 - intersection
# 计算交并比
iou = intersection / union
return iou
bbox1 = [100., 100., 200., 200.]
bbox2 = [120., 120., 220., 220.]
iou = box_iou_xyxy(bbox1, bbox2)
print('IoU is {}'.format(iou))
