本文共 3218 字，大约阅读时间需要 10 分钟。

理论参考：

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]

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