原理介绍
HOG与SVM行人检测
HOG算法是在2005年由法国Dalal提出。HOG特征作为机器学习目标检测效果最好的特征,在其基础上发展来的DPM算法更是可以成为机器学习在目标检测领域的巅峰之作,连续三年横扫PASCAL VOC。HOG是一种在计算机视觉和图像处理中用来进行物体检测的描述子。通过计算和统计局部区域的梯度方向直方图来构成特征。其主要思想就是在一幅图像中,局部目标的表象和形状能够利用梯度或边缘的方向密度分布来进行描述。其本质是梯度的统计信息,而梯度主要存在于边缘所在的地方。HOG特征具有很多优点,比如它对图像的几何和光学形变都能保持很好的不变性,可以容许行人有一些细微的肢体动作,当然,更大的肢体动作或者别的视角的行人HOG特征的处理并不好,这时候要不增加训练模板,但这会带来更大的训练开销,要不就引入部件模型,变为DPM算法。
SVM 最早是由 Vladimir N. Vapnik 和 Alexey Ya. Chervonenkis 在1963年提出,目前的版本(soft margin)是由 Corinna Cortes 和 Vapnik 在1993年提出,并在1995年发表。深度学习(2012)出现之前,SVM 被认为机器学习中近十几年来最成功,表现最好的算法。
其算法步骤大致如下:
- 假设存在一个超平面 ,表示每个样本点到平面的距离为D
- 假设正样本为+1,负样本为-1。D<0,label = -1;D>0,label = +1
- 去掉第一步D的绝对值,根据第二步可知,D * label > 0
- 求解距离平面最小的点中,最大的那个。(每一次都会产生一个平面,也就是说每一次最小的点中,距离平面的值最大的那个点)
- 特征缩放 D *label >0,将其假设为 D *label > 1,便于计算
- 得到目标函数,利用拉格朗日乘子法,利用对偶性 ,求解问题。
- 分别对w,b求导,代入原式,然后代入数据后,对拉格朗日算子求导,然后令其为0。
- 求解算子,然后回算出w,b,得到该超平面。
关于HOG和SVM的详细介绍已经原理和数学推导部分,可以参考这些文章。
HOG特征介绍(1)
HOG特征介绍(2)
SVM算法介绍
NMS非最大值抑制
在目标检测中,常常会对同一个物体检测出多个目标框,而NMS的作用是删除重复框,保留置信度分数最大的框。传统的NMS首先根据类别置信度得分对所有的目标框进行降序排列建表,然后将每个类别中置信度最高的目标框作为可靠的目标框,并分别计算其与剩余目标框的IOU,仅保留IOU小于设定阈值的目标框,以此往复循环直到结束。IOU定义为两个目标框相交面积和面积总和之比。传统的NMS算法还有不同的变种,以适合不同的使用场景,如Soft-NMS,Weighted NMS等NMS算法。基本的NMS算法过程如下:
输入: 候选边界框集合TB(每个候选框都有一个置信度)、IoU阈值N
输出: 最终的边界框集合B(初始为空集合)
- 对集合TB中的候选边框根据置信度进行降序排序;
- 从集合TB中选择置信度最高的边框,把它放入集合B中并从集合TB中删除;
- 遍历集合TB中现有的每个候选框,分别计算其与最新加入B的边界框的IoU值。如果IoU值大于阈值N,那么就把它从集合TB中删除;
- 重复步骤2~3直到集合TB为空。
具体算法介绍可以参考下面的文章:
NMS算法介绍
数据集
数据集是INRIA 数据集,该数据集使用了软链接,需要在Linux系统或者wsl(适用于Windows的Linux的子系统)下解压。该数据集中训练集有正样本 614 张(包含 1237个行人),负样本 1218张;测试集有正样本 288张(包含 589个行人),负样本 453张。更详细的介绍可以看这里。同样,想要在Windows下使用的话,这里这位作者提供了自己整理的Windows版本。
算法实现
行人检测
首先需要提取图片的HOG特征
def hog_descriptor(image):
if (image.max()-image.min()) != 0:
image = (image - image.min()) / (image.max() - image.min())
image *= 255 #这两行是对图像做归一化
image = image.astype(np.uint8)
hog = cv2.HOGDescriptor((64, 128), (16, 16), (8, 8), (8, 8), 9)
hog_feature = hog.compute(image) #提取HOG特征
return hog_feature
在这里进行图像归一化是为了减小由于局部光照变化以及前景背景对比度变化带来的影响。
接下来就是正文内容了,先导入图像,我用的数据集上面介绍的那个Windows版本的。
#导入图像
poslist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/pos')
neglist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/neg')
testlist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/normalized_images/test/pos')
testnlist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/original_images/test/neg')
显然,poslist和neglist读取的是训练集,testlist和testnlist读取的是测试集。接下来,正式读取训练集的图像,将每一张图像的HOG特征都加入列表hog_list中,标签加入列表label_list中。并且,我将负样本每张图像都随机截取了10张标准大小的也就是64×128的图像。
for i in range(len(poslist)):
posimg = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/pos',poslist[i]))
posimg = cv2.cvtColor(posimg,cv2.COLOR_RGBA2BGR)
#所用图像已经经过标准化
posimg = cv2.resize(posimg, (64, 128), interpolation=cv2.INTER_NEAREST)
pos_hog = hog_descriptor(posimg)
hog_list.append(pos_hog)
label_list.append(1)
for i in range(len(neglist)):
negimg = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/neg',neglist[i]))
negimg = cv2.cvtColor(negimg, cv2.COLOR_RGBA2BGR)
#在每张negimg图像中截取10张标准大小的图片作为负样本
for j in range(10):
y = int(random.random() * (negimg.shape[0] - 128))
x = int(random.random() * (negimg.shape[1] - 64))
negimgs = negimg[y:y + 128, x:x + 64]
negimgs = cv2.resize(negimgs, (64, 128), interpolation=cv2.INTER_NEAREST)
neg_hog = hog_descriptor(negimgs)
hog_list.append(neg_hog)
label_list.append(0)
接下来就是训练SVM模型,这里换成别的,比如LogisticRegression模型也都是可以的。
#训练SVM
clf = SVC(C=1.0, gamma='auto', kernel='rbf', probability=True)
clf.fit(hog_list.squeeze(), label_list.squeeze())
joblib.dump(clf, "D:/python work/Hog+SVM行人检测/trained_svm.m")#保存训练好的模型
同样提取HOG特征和标签列表的制作也要对训练集中的图像来一次。这里就先不放了,完整代码在最后面给出。之后就是使用之前训练好的模型在测试集上测试,并绘制PR、ROC曲线计算AUC值,AP值。
clf = joblib.load("D:/python work/Hog+SVM行人检测/trained_svm.m")
#对训练集进行预测并绘制PR、ROC曲线计算AUC值
prob = clf.predict_proba(test_hog.squeeze())[:, 1]
precision, recall, thresholds_1 = metrics.precision_recall_curve(test_label.squeeze(), prob)
plt.figure(figsize=(20, 20), dpi=100)
plt.plot(precision, recall, c='red')
plt.scatter(precision, recall, c='blue')
plt.xlabel("precision", fontdict={'size': 16})
plt.ylabel("recall", fontdict={'size': 16})
plt.title("PR_curve", fontdict={'size': 20})
plt.savefig('D:/python work/Hog+SVM行人检测/PR.png',dpi=300)
Ap=metrics.average_precision_score(test_label.squeeze(), prob)
fpr, tpr, thresholds_2 = metrics.roc_curve(test_label.squeeze(), prob, pos_label=1)
plt.figure(figsize=(20, 20), dpi=100)
plt.plot(fpr, tpr, c='red')
plt.scatter(fpr, tpr, c='blue')
plt.xlabel("FPR", fontdict={'size': 16})
plt.ylabel("TPR", fontdict={'size': 16})
plt.title("ROC_curve", fontdict={'size': 20})
plt.savefig('D:/python work/Hog+SVM行人检测/ROC.png', dpi=300)
AUC=metrics.roc_auc_score(test_label.squeeze(), prob)
print(AUC)
print(Ap)
结果最后如下所示:
PR曲线 |
ROC曲线 |
在图像上给行人画框
首先是编写用于提取HOG特征的函数,这个已经在前文中讲述过了。再就是要通过原数据集的annotations文件夹中的关于训练集正样本图像中行人的大小计算适合的window大小。
#首先通过Train中的标准的box大小计算出适合的box大小
box_list = []
ANN = os.listdir('D:/tmp-from-ubt/INRIAPerson/Train/annotations')
flag = "(Xmax, Ymax)"
for i in range(len(ANN)):
for line in open('D:/tmp-from-ubt/INRIAPerson/Train/annotations/'+ANN[i],encoding="GBK"):
if flag in line:
boxsize = line.split(flag)
boxsize = str(boxsize[1])
boxsize = boxsize.replace("(","")
boxsize = boxsize.replace(",","")
boxsize = boxsize.replace(")","")
boxsize = boxsize.replace("-","")
boxsize = boxsize.replace(":","")
boxsize = boxsize.split()
box = (float(boxsize[2])-float(boxsize[0]) ,float(boxsize[3])-float(boxsize[1]))
box_list.append(box)
box_list = np.array(box_list)
minlist = np.min(box_list,axis=0)
maxlist = np.max(box_list,axis=0)
这里面的数据集INRIAPerson是原作者Dalal的那个用软链接的数据集,这是我当时为了练习WSL采用的,用Windows版本也是可以的。将所有行人大小提取出来后,算得最小的行人框和最大的行人框分别为(23,47)和(465,831)。因此,我设计的标准行人框是64×128的,scale的倍数应当从1变化到7,才是适合所有行人大小的目标框大小。将目标框在测试集正样本的原始图像上滑动,步长为20个像素。
对每张图像截取window,并将window中的图像用之前训练好的模型检测,将框的坐标(左上角和右下角)加入边框列表,注意最后只保留了概率prob大于0.99的边框,将这些边框都传入NMS算法中(这里是mynms)。注意到给图像画框是选择了从第101个样本到最后,这里推荐只对十几二十几张图片画框就可以了,因为代码运行时间比较长,所以我最后也在i=150的时候就跳出了。
clf = joblib.load("D:/python work/Hog+SVM行人检测/trained_svm.m")
imglist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/original_images/test/pos')
for i in range(101,len(imglist)):
img = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/original_images/test/pos', imglist[i]))
img = cv2.cvtColor(img, cv2.COLOR_RGBA2BGR)
h,w,c= img.shape
patch_list = []
hog_feature = []
box_list = []
for j in range(minscale,maxscale+1,1):
winsize = [j*64,j*128]
for m in range(0,h-winsize[1],20):
for n in range(0,w-winsize[0],20):
patch = img[m:m+winsize[1],n:n+winsize[0]]
patch = cv2.resize(patch, (64,128), interpolation = cv2.INTER_NEAREST)
boxcoord = (m,n,m+winsize[1],n+winsize[0])
hogfea = hog_descriptor(patch)
hog_feature.append(hogfea)
box_list.append(boxcoord)
patch_list.append(patch)
hog_feature = np.array(hog_feature).squeeze()
box_list = np.array(box_list)
prob = clf.predict_proba(hog_feature)[:, 1]
mask = (prob>= 0.99)
box_list = box_list[mask]
prob = prob[mask]
boxzhong = mynms(box_list,prob)
for k in range(len(boxzhong)):
cv2.rectangle(img, (boxzhong[k][1], boxzhong[k][0]), (boxzhong[k][3], boxzhong[k][2]),(0, 0, 255),3)
cv2.imwrite('D:/jupyterwork/result/'+imglist[i]+".jpg",img)
print(str(i))
if i == 150:
break
接下来展示一下具体的NMS算法如何实现。这里我阈值选择的是0.8。
def mynms(box_list,prob_list,threshold=0.8):
x1 = box_list[:,0]
y1 = box_list[:,1]
x2 = box_list[:,2]
y2 = box_list[:,3]
areas = (x2-x1+1)*(y2-y1+1)
box_result = []
flag = []
index = prob_list.argsort()[::-1] #想要从大到小排序
while index.size>0:
i = index[0] #第一个,也就是概率最大(得分最高)的那个框
flag.append(i)
x11 = np.maximum(x1[i], x1[index[1:]]) # calculate the points of overlap
y11 = np.maximum(y1[i], y1[index[1:]])
x22 = np.minimum(x2[i], x2[index[1:]])
y22 = np.minimum(y2[i], y2[index[1:]])
w = np.maximum(0, x22 - x11 + 1)
h = np.maximum(0, y22 - y11 + 1)
overlaps = w * h
ious = overlaps / (areas[i] + areas[index[1:]] - overlaps)
#idx = np.where(ious < threshold)[0]
index = np.delete(index,np.concatenate(([0],np.where(ious < threshold)[0])))
#index = index[idx + 1]
return box_list[flag].astype("int")
完整代码
注意一下,代码中间有些注释什么的是在调试过程中加的,加不加都无所谓。
目标检测
import cv2
import os
import numpy as np
import os.path as osp
from skimage import io
import random
from sklearn import metrics
from sklearn.svm import SVC
import matplotlib.pyplot as plt
import joblib
#对数据进行处理,提取正负样本的Hog特征
#计算传入图像的HOG特征
def hog_descriptor(image):
if (image.max()-image.min()) != 0:
image = (image - image.min()) / (image.max() - image.min())
image *= 255
image = image.astype(np.uint8)
hog = cv2.HOGDescriptor((64, 128), (16, 16), (8, 8), (8, 8), 9)
hog_feature = hog.compute(image)
return hog_feature
#导入图像
poslist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/pos')
neglist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/neg')
testlist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/normalized_images/test/pos')
testnlist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/original_images/test/neg')
#获得正样本和负样本的HOG特征,并标记
hog_list = []
label_list = []
print("正样本图像有"+str(len(poslist)))
print("负样本原始图像有"+str(len(neglist))+",每个原始图像提供十个负样本")
for i in range(len(poslist)):
posimg = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/pos',poslist[i]))
posimg = cv2.cvtColor(posimg,cv2.COLOR_RGBA2BGR)
#所用图像已经经过标准化
posimg = cv2.resize(posimg, (64, 128), interpolation=cv2.INTER_NEAREST)
pos_hog = hog_descriptor(posimg)
hog_list.append(pos_hog)
label_list.append(1)
for i in range(len(neglist)):
negimg = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/normalized_images/train/neg',neglist[i]))
negimg = cv2.cvtColor(negimg, cv2.COLOR_RGBA2BGR)
#在每张negimg图像中截取10张标准大小的图片作为负样本
for j in range(10):
y = int(random.random() * (negimg.shape[0] - 128))
x = int(random.random() * (negimg.shape[1] - 64))
negimgs = negimg[y:y + 128, x:x + 64]
negimgs = cv2.resize(negimgs, (64, 128), interpolation=cv2.INTER_NEAREST)
neg_hog = hog_descriptor(negimgs)
hog_list.append(neg_hog)
label_list.append(0)
print(type(hog_list[10]))
print(type(hog_list[-10]))
hog_list = np.float32(hog_list)
label_list = np.int32(label_list).reshape(len(label_list),1)
#训练SVM,并在Test上测试
clf = SVC(C=1.0, gamma='auto', kernel='rbf', probability=True)
clf.fit(hog_list.squeeze(), label_list.squeeze())
joblib.dump(clf, "D:/python work/Hog+SVM行人检测/trained_svm.m")
#提取训练集样本和标签
test_hog = []
test_label = []
for i in range(len(testlist)):
testimg = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/normalized_images/test/pos', testlist[i]))
testimg = cv2.cvtColor(testimg, cv2.COLOR_RGBA2BGR)
testimg = cv2.resize(testimg, (64, 128), interpolation=cv2.INTER_NEAREST)
testhog = hog_descriptor(testimg)
test_hog.append(testhog)
test_label.append(1)
for i in range(len(testnlist)):
testnegimg = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/original_images/test/neg',testnlist[i]))
testnegimg = cv2.cvtColor(testnegimg, cv2.COLOR_RGBA2BGR)
#在每张negimg图像中截取10张标准大小的图片作为负样本
for j in range(10):
y = int(random.random() * (testnegimg.shape[0] - 128))
x = int(random.random() * (testnegimg.shape[1] - 64))
testnegimgs = testnegimg[y:y + 128, x:x + 64]
testnegimgs = cv2.resize(testnegimgs, (64, 128), interpolation=cv2.INTER_NEAREST)
testneg_hog = hog_descriptor(testnegimgs)
test_hog.append(testneg_hog)
test_label.append(0)
test_hog = np.float32(test_hog)
test_label = np.int32(test_label).reshape(len(test_label),1)
#可以导入训练后的SVM
clf = joblib.load("D:/python work/Hog+SVM行人检测/trained_svm.m")
#对训练集进行预测并绘制PR、ROC曲线计算AUC值
prob = clf.predict_proba(test_hog.squeeze())[:, 1]
precision, recall, thresholds_1 = metrics.precision_recall_curve(test_label.squeeze(), prob)
plt.figure(figsize=(20, 20), dpi=100)
plt.plot(precision, recall, c='red')
plt.scatter(precision, recall, c='blue')
plt.xlabel("precision", fontdict={'size': 16})
plt.ylabel("recall", fontdict={'size': 16})
plt.title("PR_curve", fontdict={'size': 20})
plt.savefig('D:/python work/Hog+SVM行人检测/PR.png',dpi=300)
Ap=metrics.average_precision_score(test_label.squeeze(), prob)
fpr, tpr, thresholds_2 = metrics.roc_curve(test_label.squeeze(), prob, pos_label=1)
plt.figure(figsize=(20, 20), dpi=100)
plt.plot(fpr, tpr, c='red')
plt.scatter(fpr, tpr, c='blue')
plt.xlabel("FPR", fontdict={'size': 16})
plt.ylabel("TPR", fontdict={'size': 16})
plt.title("ROC_curve", fontdict={'size': 20})
plt.savefig('D:/python work/Hog+SVM行人检测/ROC.png', dpi=300)
AUC=metrics.roc_auc_score(test_label.squeeze(), prob)
print(AUC)
print(Ap)
给图像画框文章来源:https://www.toymoban.com/news/detail-419071.html
import cv2
import os
import numpy as np
import os.path as osp
from skimage import io
import random
from sklearn import metrics
from sklearn.svm import SVC
import matplotlib.pyplot as plt
import joblib
import math
def hog_descriptor(image):
if (image.max()-image.min()) != 0:
image = (image - image.min()) / (image.max() - image.min())
image *= 255
image = image.astype(np.uint8)
hog = cv2.HOGDescriptor((64, 128), (16, 16), (8, 8), (8, 8), 9)
hog_feature = hog.compute(image)
return hog_feature
def mynms(box_list,prob_list,threshold=0.8):
x1 = box_list[:,0]
y1 = box_list[:,1]
x2 = box_list[:,2]
y2 = box_list[:,3]
areas = (x2-x1+1)*(y2-y1+1)
box_result = []
flag = []
index = prob_list.argsort()[::-1] #想要从大到小排序
while index.size>0:
i = index[0]
flag.append(i)
x11 = np.maximum(x1[i], x1[index[1:]]) # calculate the points of overlap
y11 = np.maximum(y1[i], y1[index[1:]])
x22 = np.minimum(x2[i], x2[index[1:]])
y22 = np.minimum(y2[i], y2[index[1:]])
w = np.maximum(0, x22 - x11 + 1)
h = np.maximum(0, y22 - y11 + 1)
overlaps = w * h
ious = overlaps / (areas[i] + areas[index[1:]] - overlaps)
#idx = np.where(ious < threshold)[0]
index = np.delete(index,np.concatenate(([0],np.where(ious < threshold)[0])))
#index = index[idx + 1]
return box_list[flag].astype("int")
#首先通过Train中的标准的box大小计算出适合的box大小
box_list = []
ANN = os.listdir('D:/tmp-from-ubt/INRIAPerson/Train/annotations')
flag = "(Xmax, Ymax)"
for i in range(len(ANN)):
for line in open('D:/tmp-from-ubt/INRIAPerson/Train/annotations/'+ANN[i],encoding="GBK"):
if flag in line:
boxsize = line.split(flag)
boxsize = str(boxsize[1])
boxsize = boxsize.replace("(","")
boxsize = boxsize.replace(",","")
boxsize = boxsize.replace(")","")
boxsize = boxsize.replace("-","")
boxsize = boxsize.replace(":","")
boxsize = boxsize.split()
box = (float(boxsize[2])-float(boxsize[0]) ,float(boxsize[3])-float(boxsize[1]))
box_list.append(box)
box_list = np.array(box_list)
minlist = np.min(box_list,axis=0)
maxlist = np.max(box_list,axis=0)
"""
print(minlist)
print(maxlist)
"""
minscale = min(minlist[0]/64,minlist[1]/128)
maxscale = min(maxlist[0]/64,maxlist[1]/128)
"""
print(minscale)
print(maxscale)
"""
minscale = math.ceil(minscale)
maxscale = math.ceil(maxscale)
print(minscale)
print(maxscale)
clf = joblib.load("D:/python work/Hog+SVM行人检测/trained_svm.m")
imglist = os.listdir('D:/DataSet/INRIADATA/INRIADATA/original_images/test/pos')
for i in range(101,len(imglist)):
img = io.imread(osp.join('D:/DataSet/INRIADATA/INRIADATA/original_images/test/pos', imglist[i]))
img = cv2.cvtColor(img, cv2.COLOR_RGBA2BGR)
h,w,c= img.shape
patch_list = []
hog_feature = []
box_list = []
for j in range(minscale,maxscale+1,1):
winsize = [j*64,j*128]
for m in range(0,h-winsize[1],20):
for n in range(0,w-winsize[0],20):
patch = img[m:m+winsize[1],n:n+winsize[0]]
patch = cv2.resize(patch, (64,128), interpolation = cv2.INTER_NEAREST)
boxcoord = (m,n,m+winsize[1],n+winsize[0])
hogfea = hog_descriptor(patch)
hog_feature.append(hogfea)
box_list.append(boxcoord)
patch_list.append(patch)
hog_feature = np.array(hog_feature).squeeze()
box_list = np.array(box_list)
prob = clf.predict_proba(hog_feature)[:, 1]
mask = (prob>= 0.99)
box_list = box_list[mask]
prob = prob[mask]
boxzhong = mynms(box_list,prob)
for k in range(len(boxzhong)):
cv2.rectangle(img, (boxzhong[k][1], boxzhong[k][0]), (boxzhong[k][3], boxzhong[k][2]),(0, 0, 255),3)
cv2.imwrite('D:/jupyterwork/result/'+imglist[i]+".jpg",img)
print(str(i))
if i == 150:
break
print("结束")
Reference
https://blog.csdn.net/weixin_44505390/article/details/107161828
https://zhuanlan.zhihu.com/p/40960756
https://zhuanlan.zhihu.com/p/74591258
https://zhuanlan.zhihu.com/p/405527616
https://blog.csdn.net/c2250645962/article/details/106476147文章来源地址https://www.toymoban.com/news/detail-419071.html
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