交併比IOU

交併比（Intersection-over-Union，IoU），目標檢測中使用的一個概念，是產生的候選框（candidate bound）與原標記框（ground truth bound）的交疊率，即它們的交集與並集的比值。最理想情況是完全重疊，即比值爲1。

計算公式：

Python實現代碼：

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的面積
    garea = (gx2 - gx1) * (gy2 - gy1) #G的面積

    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的面積
 iou = area / (carea + garea - area)
 return iou