deeplearning.ai 总结 - 交并比（Intersection-over-Union，IoU）

deeplearning.ai 总结 - 交并比（Intersection-over-Union，IoU）

flyfish

C++代码实现

we define a box using its two corners (upper left and lower right): (x1, y1, x2, y2) rather than the midpoint and height/width.
To calculate the area of a rectangle you need to multiply its height (y2 - y1) by its width (x2 - x1).

按照描述 坐标是这样的，x1, y1, x2, y2，分别是向量的下标，0,1,2,3

最后IoU的计算是这样的

C++代码实现

//函数定义 交并比（Intersection-over-Union，IoU）
double iou(std::vector<int>& box1, std::vector<int>& box2){

    int xi1 = std::max(box1[0],box2[0]);
    int yi1 = std::max(box1[1], box2[1]); 
    int xi2 = std::min(box1[2], box2[2]);
    int yi2 = std::min(box1[3], box2[3]);

    //交集 ,注意的地方在两个矩形不相交时，xi2 - xi1 会产生负数，yi2 - yi1 同理
    int inter_area = std::max(0, xi2 - xi1)*std::max(0, yi2 - yi1);
    int box1_area = (box1[2] - box1[0])*(box1[3] - box1[1]);//矩形1的面积
    int box2_area = (box2[2] - box2[0])*(box2[3] - box2[1]);//矩形2的面积

    int union_area = box1_area + box2_area - inter_area; //并集

    double r = static_cast<double>(inter_area) / static_cast<double>(union_area);

    return r;
}

 //调用
std::vector<int> box1 = { 2, 1, 4, 3 };
std::vector<int> box2 = { 1, 2, 3, 4 };
double d = iou(box1, box2);