图像处理的交并比（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：

Python实现代码：

def calculateIoU(candidateBound, groundTruthBound):
cx1 = candidateBound[0]
cy1 = candidateBound[1]
cx2 = candidateBound[2]
cy2 = candidateBound[3]

gx1 = groundTruthBound[0]
gy1 = groundTruthBound[1]
gx2 = groundTruthBound[2]
gy2 = groundTruthBound[3]

carea = (cx2 - cx1) * (cy2 - cy1) #C的面积
garea = (gx2 - gx1) * (gy2 - gy1) #G的面积

x1 = max(cx1, gx1)
y1 = min(cy1, gy1)
x2 = min(cx2, gx2)
y2 = max(cy2, gy2)
w = max(0, x2 - x1)
h = max(0, y2 - y1)
area = w * h #C∩G的面积

iou = area / (carea + garea - area)

return iou