kmeans_for_anchors.py

#-------------------------------------------------------------------------------------------------------#
#   kmeans虽然会对数据集中的框进行聚类，但是很多数据集由于框的大小相近，聚类出来的9个框相差不大，
#   这样的框反而不利于模型的训练。因为不同的特征层适合不同大小的先验框，shape越小的特征层适合越大的先验框
#   原始网络的先验框已经按大中小比例分配好了，不进行聚类也会有非常好的效果。
#-------------------------------------------------------------------------------------------------------#
import glob
import xml.etree.ElementTree as ET

import matplotlib.pyplot as plt
import numpy as np
from tqdm import tqdm


def cas_ratio(box,cluster):
    ratios_of_box_cluster = box / cluster
    ratios_of_cluster_box = cluster / box
    ratios = np.concatenate([ratios_of_box_cluster, ratios_of_cluster_box], axis = -1)

    return np.max(ratios, -1)

def avg_ratio(box,cluster):
    return np.mean([np.min(cas_ratio(box[i],cluster)) for i in range(box.shape[0])])

def kmeans(box,k):
    #-------------------------------------------------------------#
    #   取出一共有多少框
    #-------------------------------------------------------------#
    row = box.shape[0]
    
    #-------------------------------------------------------------#
    #   每个框各个点的位置
    #-------------------------------------------------------------#
    distance = np.empty((row,k))
    
    #-------------------------------------------------------------#
    #   最后的聚类位置
    #-------------------------------------------------------------#
    last_clu = np.zeros((row,))

    np.random.seed()

    #-------------------------------------------------------------#
    #   随机选5个当聚类中心
    #-------------------------------------------------------------#
    cluster = box[np.random.choice(row,k,replace = False)]

    iter = 0
    while True:
        #-------------------------------------------------------------#
        #   计算当前框和先验框的宽高比例
        #-------------------------------------------------------------#
        for i in range(row):
            distance[i] = cas_ratio(box[i],cluster)
        
        #-------------------------------------------------------------#
        #   取出最小点
        #-------------------------------------------------------------#
        near = np.argmin(distance,axis=1)

        if (last_clu == near).all():
            break
        
        #-------------------------------------------------------------#
        #   求每一个类的中位点
        #-------------------------------------------------------------#
        for j in range(k):
            cluster[j] = np.median(
                box[near == j],axis=0)

        last_clu = near
        if iter % 5 == 0:
            print('iter: {:d}. avg_ratio:{:.2f}'.format(iter, avg_ratio(box,cluster)))
        iter += 1

    return cluster, near

def load_data(path):
    data = []
    #-------------------------------------------------------------#
    #   对于每一个xml都寻找box
    #-------------------------------------------------------------#
    for xml_file in tqdm(glob.glob('{}/*xml'.format(path))):
        tree = ET.parse(xml_file)
        height = int(tree.findtext('./size/height'))
        width = int(tree.findtext('./size/width'))
        if height<=0 or width<=0:
            continue
        
        #-------------------------------------------------------------#
        #   对于每一个目标都获得它的宽高
        #-------------------------------------------------------------#
        for obj in tree.iter('object'):
            xmin = int(float(obj.findtext('bndbox/xmin'))) / width
            ymin = int(float(obj.findtext('bndbox/ymin'))) / height
            xmax = int(float(obj.findtext('bndbox/xmax'))) / width
            ymax = int(float(obj.findtext('bndbox/ymax'))) / height

            xmin = np.float64(xmin)
            ymin = np.float64(ymin)
            xmax = np.float64(xmax)
            ymax = np.float64(ymax)
            # 得到宽高
            data.append([xmax-xmin,ymax-ymin])
    return np.array(data)

if __name__ == '__main__':
    np.random.seed(0)
    #-------------------------------------------------------------#
    #   运行该程序会计算'./VOCdevkit/VOC2007/Annotations'的xml
    #   会生成yolo_anchors.txt
    #-------------------------------------------------------------#
    input_shape = [640, 640]
    anchors_num = 9
    #-------------------------------------------------------------#
    #   载入数据集，可以使用VOC的xml
    #-------------------------------------------------------------#
    path        = 'VOCdevkit/VOC2007/Annotations'
    
    #-------------------------------------------------------------#
    #   载入所有的xml
    #   存储格式为转化为比例后的width,height
    #-------------------------------------------------------------#
    print('Load xmls.')
    data = load_data(path)
    print('Load xmls done.')
    
    #-------------------------------------------------------------#
    #   使用k聚类算法
    #-------------------------------------------------------------#
    print('K-means boxes.')
    cluster, near   = kmeans(data, anchors_num)
    print('K-means boxes done.')
    data            = data * np.array([input_shape[1], input_shape[0]])
    cluster         = cluster * np.array([input_shape[1], input_shape[0]])

    #-------------------------------------------------------------#
    #   绘图
    #-------------------------------------------------------------#
    for j in range(anchors_num):
        plt.scatter(data[near == j][:,0], data[near == j][:,1])
        plt.scatter(cluster[j][0], cluster[j][1], marker='x', c='black')
    plt.savefig("kmeans_for_anchors.jpg")
    plt.show()
    print('Save kmeans_for_anchors.jpg in root dir.')

    cluster = cluster[np.argsort(cluster[:, 0] * cluster[:, 1])]
    print('avg_ratio:{:.2f}'.format(avg_ratio(data, cluster)))
    print(cluster)

    f = open("yolo_anchors.txt", 'w')
    row = np.shape(cluster)[0]
    for i in range(row):
        if i == 0:
            x_y = "%d,%d" % (cluster[i][0], cluster[i][1])
        else:
            x_y = ", %d,%d" % (cluster[i][0], cluster[i][1])
        f.write(x_y)
    f.close()