MNS(非极大值抑制)python实现

布满荆棘的人生 2022-12-26 00:48 124阅读 0赞

理论参考：[https://blog.csdn.net/a1103688841/article/details/89711120][https_blog.csdn.net_a1103688841_article_details_89711120]

源码：

import numpy as np
     
    def py_cpu_nms(dets, thresh):
        
        # 单独获取各个参数，以下参数shape = (5,)
        x1 = dets[:,0]
        y1 = dets[:,1]
        x2 = dets[:,2]
        y2 = dets[:,3]
        scores = dets[:,4]
        areas = (y2-y1+1) * (x2-x1+1)
        print("areas.shape: {}".format(areas.shape))
        print("areas: {}".format(areas))
    
        keep = []
    
        # 得分按照由高到低排序的索引, index.shape = (6,)
        index = scores.argsort()[::-1]
        print("index.shape: {}".format(index.shape))
        print("index: {}".format(index))
    
        while index.size >0:
            # i为得分最高的索引
            i = index[0]      
    
            # 将得分最高的索引追加到列表中
            keep.append(i)
    
            # 计算两个box左上角点坐标的最大值x11、y11和右下角坐标的最小值x22、y22
            # x11、y11、x22、y22 shape = (5,)
            x11 = np.maximum(x1[i], x1[index[1:]])
            y11 = np.maximum(y1[i], y1[index[1:]])
            x22 = np.minimum(x2[i], x2[index[1:]])
            y22 = np.minimum(y2[i], y2[index[1:]])
            print("index[1:]: {}".format(index[1:]))
            print("x1[index[1:]]: {}".format(x1[index[1:]]))
            print("x11: {}".format(x11))
            print("x11.shape: {}".format(x11.shape))
    
            # 当两个方框相交时，22-11最后得到w,h是正值
            # 当两个方框不相交的时候，22-11最后得到w,h是负值，则设置为0
            # w、h shape = (5,)
            w = np.maximum(0, x22-x11+1)
            h = np.maximum(0, y22-y11+1)
            print("w: {}".format(w))
            print("w.shape: {}".format(w.shape))
    
            # 计算交集面积
            # overlaps.shape = (5,)
            overlaps = w * h
            print("overlaps: {}".format(overlaps))
            print("overlaps.shape: {}".format(overlaps.shape))
    
            # 计算交并比
            # ious.shape = (5,)
            ious = overlaps / (areas[i] + areas[index[1:]] - overlaps)
            print("ious.shape: {}".format(ious.shape))
            print("ious: {}".format(ious))
    
            # 得到满足阈值条件的ious中的索引(ious相比index缺少第一个最大值)
            ious_idx = np.where(ious<=thresh)[0]
            print("ious<=thres idx: {}".format(ious_idx))
            # ious_idx+1得到在index中的索引
            index = index[ious_idx + 1]   # because index start from 1
            print("index: {}".format(index))
     
        return keep
     
    if __name__ == "__main__":
    
        boxes=np.array([[100,100,210,210,0.72], # 0
                        [250,250,420,420,0.8],  # 1
                        [220,220,320,330,0.92], # 2
                        [100,100,210,210,0.72], # 3
                        [230,240,325,330,0.81], # 4
                        [220,230,315,340,0.9]]) # 5
    
        keep = py_cpu_nms(boxes, thresh=0.7)
        print("keep: {}".format(keep))

输出：

areas.shape: (6,)
    areas: [ 12321.  29241.  11211.  12321.   8736.  10656.]
    index.shape: (6,)
    index: [2 5 4 1 3 0]
    index[1:]: [5 4 1 3 0]
    x1[index[1:]]: [ 220.  230.  250.  100.  100.]
    x11: [ 220.  230.  250.  220.  220.]
    x11.shape: (5,)
    w: [ 96.  91.  71.   0.   0.]
    w.shape: (5,)
    overlaps: [ 9696.  8281.  5751.     0.     0.]
    overlaps.shape: (5,)
    ious.shape: (5,)
    ious: [ 0.79664777  0.70984056  0.16573009  0.          0.        ]
    ious<=thres idx: [2 3 4]
    index: [1 3 0]
    index[1:]: [3 0]
    x1[index[1:]]: [ 100.  100.]
    x11: [ 250.  250.]
    x11.shape: (2,)
    w: [ 0.  0.]
    w.shape: (2,)
    overlaps: [ 0.  0.]
    overlaps.shape: (2,)
    ious.shape: (2,)
    ious: [ 0.  0.]
    ious<=thres idx: [0 1]
    index: [3 0]
    index[1:]: [0]
    x1[index[1:]]: [ 100.]
    x11: [ 100.]
    x11.shape: (1,)
    w: [ 111.]
    w.shape: (1,)
    overlaps: [ 12321.]
    overlaps.shape: (1,)
    ious.shape: (1,)
    ious: [ 1.]
    ious<=thres idx: []
    index: []
    keep: [2, 1, 3]

[https_blog.csdn.net_a1103688841_article_details_89711120]: https://blog.csdn.net/a1103688841/article/details/89711120