1 %% NMS:non maximum suppression
 2 function pick = nms(boxes,threshold,type)
 3 % boxes: m x 5,表示有m个框，5列分别是[x1 y1 x2 y2 score]
 4 % threshold: IOU阈值
 5 % type：IOU阈值的定义类型
 6
 7     % 输入为空，则直接返回
 8     if isempty(boxes)
 9       pick = [];
10       return;
11     end
12
13     % 依次取出左上角和右下角坐标以及分类器得分(置信度)
14     x1 = boxes(:,1);
15     y1 = boxes(:,2);
16     x2 = boxes(:,3);
17     y2 = boxes(:,4);
18     s = boxes(:,5);
19
20     % 计算每一个框的面积
21     area = (x2-x1+1) .* (y2-y1+1);
22
23     %将得分升序排列
24     [vals, I] = sort(s);
25
26     %初始化
27     pick = s*0;
28     counter = 1;
29
30     % 循环直至所有框处理完成
31     while ~isempty(I)
32         last = length(I); %当前剩余框的数量
33         i = I(last);%选中最后一个，即得分最高的框
34         pick(counter) = i;
35         counter = counter + 1;
36
37         %计算相交面积
38         xx1 = max(x1(i), x1(I(1:last-1)));
39         yy1 = max(y1(i), y1(I(1:last-1)));
40         xx2 = min(x2(i), x2(I(1:last-1)));
41         yy2 = min(y2(i), y2(I(1:last-1)));
42         w = max(0.0, xx2-xx1+1);
43         h = max(0.0, yy2-yy1+1);
44         inter = w.*h;
45
46         %不同定义下的IOU
47         if strcmp(type,'Min')
48             %重叠面积与最小框面积的比值
49             o = inter ./ min(area(i),area(I(1:last-1)));
50         else
51             %交集/并集
52             o = inter ./ (area(i) + area(I(1:last-1)) - inter);
53         end
54
55         %保留所有重叠面积小于阈值的框，留作下次处理
56         I = I(find(o<=threshold));
57     end
58     pick = pick(1:(counter-1));
59 end