PyTorch复现VGG学习笔记

PyTorch复现ResNet学习笔记

一篇简单的学习笔记，实现五类花分类，这里只介绍复现的一些细节

如果想了解更多有关网络的细节，请去看论文《VERY DEEP CONVOLUTIONAL NETWORKS FOR LARGE-SCALE IMAGE RECOGNITION》

简单说明下数据集，下载链接,这里用的数据与AlexNet的那篇是一样的所以不在说明

一、环境准备

可以去看之前的一篇博客，里面写的很详细了，并且推荐了一篇炮哥的环境搭建环境

• Anaconda3（建议使用）
• python=3.6/3.7/3.8
• pycharm (IDE)
• pytorch=1.11.0 (pip package)
• torchvision=0.12.0 (pip package)
• cudatoolkit=11.3

二、模型搭建、训练

1.整体框图

模型输入为224*224，采用的预处理方式：从每个像素中减去在训练集上计算的RGB均值

vgg11层到19层的结构

其中最常用的是VGG-16，在本文中用的也是16层的D网络，全是步长为3的卷积

计算层数：只计算有参数的层，池化层没参数不计入这里16=13(卷积层)+3(全连接)

 总结：

1.局部相应归一化LRN对模型没有改善，A与A-LRN比较

2.1×1的卷积核带来非线性函数有帮助(C优于B)，但也可以用(non-trivial receptive fields)来代替，非平凡，无法证明

3.具有小滤波器的深层网络优于具有较大滤波器的浅层网络。

4.深度越深效果越好(A 与 B, C, D, E 比较),19层饱和(需要更多的数据集)

2.net.py

网络整体结构代码

 1 #迁移学习，使用vgg与训练权重vgg16.pth
 2 import torch.nn as nn
 3 import torch
 4
 5 # official pretrain weights
 6 model_urls = {
 7     'vgg11': 'https://download.pytorch.org/models/vgg11-bbd30ac9.pth',
 8     'vgg13': 'https://download.pytorch.org/models/vgg13-c768596a.pth',
 9     'vgg16': 'https://download.pytorch.org/models/vgg16-397923af.pth',
10     'vgg19': 'https://download.pytorch.org/models/vgg19-dcbb9e9d.pth'
11 }
12
13 class VGG(nn.Module):
14     def __init__(self, features, num_classes=1000, init_weights=False):
15         super(VGG, self).__init__()
16         self.features = features
17         self.classifier = nn.Sequential(
18             nn.Linear(512*7*7, 4096),
19             nn.ReLU(True),
20             nn.Dropout(p=0.5),
21             nn.Linear(4096, 4096),
22             nn.ReLU(True),
23             nn.Dropout(p=0.5),
24             nn.Linear(4096, num_classes)
25         )
26         if init_weights:
27             self._initialize_weights()
28
29     def forward(self, x):
30         # N x 3 x 224 x 224
31         x = self.features(x)
32         # N x 512 x 7 x 7
33         x = torch.flatten(x, start_dim=1)
34         # N x 512*7*7
35         x = self.classifier(x)
36         return x
37
38     def _initialize_weights(self):
39         for m in self.modules():
40             if isinstance(m, nn.Conv2d):
41                 # nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
42                 nn.init.xavier_uniform_(m.weight)
43                 if m.bias is not None:
44                     nn.init.constant_(m.bias, 0)
45             elif isinstance(m, nn.Linear):
46                 nn.init.xavier_uniform_(m.weight)
47                 # nn.init.normal_(m.weight, 0, 0.01)
48                 nn.init.constant_(m.bias, 0)
49
50
51 def make_features(cfg: list):
52     layers = []
53     in_channels = 3
54     for v in cfg:
55         if v == "M":
56             layers += [nn.MaxPool2d(kernel_size=2, stride=2)]
57         else:
58             conv2d = nn.Conv2d(in_channels, v, kernel_size=3, padding=1)
59             layers += [conv2d, nn.ReLU(True)]
60             in_channels = v
61     return nn.Sequential(*layers)
62
63
64 cfgs = {
65     'vgg11': [64, 'M', 128, 'M', 256, 256, 'M', 512, 512, 'M', 512, 512, 'M'],
66     'vgg13': [64, 64, 'M', 128, 128, 'M', 256, 256, 'M', 512, 512, 'M', 512, 512, 'M'],
67     'vgg16': [64, 64, 'M', 128, 128, 'M', 256, 256, 256, 'M', 512, 512, 512, 'M', 512, 512, 512, 'M'],
68     'vgg19': [64, 64, 'M', 128, 128, 'M', 256, 256, 256, 256, 'M', 512, 512, 512, 512, 'M', 512, 512, 512, 512, 'M'],
69 }
70
71
72 def vgg(model_name="vgg16", **kwargs):
73     assert model_name in cfgs, "Warning: model number {} not in cfgs dict!".format(model_name)
74     cfg = cfgs[model_name]
75
76     model = VGG(make_features(cfg), **kwargs)
77     return model
78 if __name__ =="__main__":
79     x = torch.rand([1, 3, 224, 224])
80     model = vgg(num_classes=5)
81     y = model(x)
82     #print(y)
83
84     #统计模型参数
85     sum = 0
86     for name, param in model.named_parameters():
87         num = 1
88         for size in param.shape:
89             num *= size
90         sum += num
91         #print("{:30s} : {}".format(name, param.shape))
92     print("total param num {}".format(sum))#total param num 134,281,029

net.py

写完后保存，运行可以检查是否报错

如果需要打印模型参数，将代码注释去掉即可，得到googlenet的参数为134,281,029,有一亿多的参数，可以说是很多了

3.数据划分

这里与AlexNet用的一样

分好后的数据集

运行下面代码将数据按一定比例，划分为训练集和验证集

数据划分的代码

4.train.py

这里训练我们使用迁移学习，来减少训练时间

因为要自己训练的话不仅要花大量时间，而且博主也尝试了训练大概有50个epoch，发现模型一直没在训练

可以看到训练集和验证集的准确率一直在24%左右跳动

所以我们加载vgg的预训练权重，这里给上vgg16的预训练权重

链接：https://pan.baidu.com/s/1U-fOe2Hll368CQIFLS-SNw?pwd=gfxp
提取码：gfxp

  1 import torch
  2 from torch import nn
  3 from torchvision import transforms,datasets
  4 from torch import optim
  5 from torch.optim import lr_scheduler
  6 from net import vgg
  7 import os
  8 import sys
  9 import json
 10 from torch.utils.data import DataLoader
 11 from tqdm import tqdm#用于画进度条
 12 import matplotlib.pyplot as plt
 13 from matplotlib.ticker import MaxNLocator
 14
 15 # 如果显卡可用，则用显卡进行训练
 16 device = 'cuda' if torch.cuda.is_available() else 'cpu'
 17 print("using {} device".format(device))
 18 print(device)
 19
 20 data_transform = {
 21     "train":transforms.Compose([
 22         transforms.RandomResizedCrop(224),#随机裁剪
 23         transforms.RandomVerticalFlip(),#随机垂直翻转
 24         transforms.ToTensor(),#转换为tensor格式
 25         transforms.Normalize((0.5, 0.5, 0.5),(0.5, 0.5, 0.5))#RGB三通道
 26                                 ]),
 27     "val":transforms.Compose([
 28         transforms.Resize((224,224)),
 29         transforms.ToTensor(),
 30         transforms.Normalize((0.5, 0.5, 0.5),(0.5, 0.5, 0.5))
 31     ])
 32 }
 33 #数据集路径
 34 ROOT_TRAIN = 'data/train'
 35 ROOT_TEST = 'data/val'
 36
 37 batch_size = 16
 38
 39 train_dataset = datasets.ImageFolder(ROOT_TRAIN,transform=data_transform["train"])
 40 val_dataset = datasets.ImageFolder(ROOT_TEST,transform=data_transform["val"])
 41
 42 train_dataloader = DataLoader(train_dataset,batch_size=batch_size,shuffle=True)
 43 val_dataloader = DataLoader(val_dataset,batch_size=batch_size,shuffle=True)
 44
 45 train_num = len(train_dataset)#计数
 46 val_num = len(val_dataset)
 47 print("using {} images for training, {} images for validation.".format(train_num,val_num))
 48
 49 #将#{'daisy':0, 'dandelion':1, 'roses':2, 'sunflower':3, 'tulips':4}键值对值反转，并保存
 50 flower_list = train_dataset.class_to_idx
 51 cla_dict = dict((val, key) for key, val in flower_list.items())
 52 # write dict into json file
 53 json_str = json.dumps(cla_dict, indent=4)
 54 with open('class_indices.json', 'w') as json_file:
 55     json_file.write(json_str)#保存json文件(好处，方便转换为其它类型数据)用于预测用
 56
 57 model_name = "vgg16"
 58 model = vgg(model_name,num_classes=5,init_weights=True)
 59
 60 # 加载预训练模型
 61 model_weights_path = './vgg16.pth'
 62 ckpt = torch.load(model_weights_path)
 63 ckpt.pop('classifier.6.weight')
 64 ckpt.pop('classifier.6.bias')
 65 missing_keys, unexpected_keys = model.load_state_dict(ckpt, strict=False)
 66
 67 model.to(device)
 68
 69 loss_fn = nn.CrossEntropyLoss()
 70 #定义优化器
 71 optimizer = optim.SGD(model.parameters(),lr=0.003)
 72 #学习率每隔10epoch变为原来的0.1
 73 lr_s = lr_scheduler.StepLR(optimizer, step_size=10, gamma=0.5)
 74
 75 #定义训练函数
 76     def train(dataloader,model,loss_fn,optimizer):
 77         model.train()
 78         loss,acc,n = 0.0,0.0,0
 79         train_bar = tqdm(dataloader,file=sys.stdout)
 80         for batch,(x,y) in enumerate(train_bar):
 81             #前向传播
 82             x,y = x.to(device),y.to(device)
 83             output = model(x)
 84             cur_loss = loss_fn(output,y)
 85             _,pred = torch.max(output,axis=-1)
 86             cur_acc = torch.sum(y==pred)/output.shape[0]
 87             #反向传播
 88             optimizer.zero_grad()#梯度清零
 89             cur_loss.backward()
 90             optimizer.step()
 91             loss += cur_loss
 92             acc += cur_acc
 93             n += 1
 94             train_bar.desc = "train epoch[{}/{}] loss:{:.3f}".format(i+1,epoch,cur_loss)
 95         train_loss = loss / n
 96         train_acc = acc / n
 97         print(f"train_loss:{train_loss}")
 98         print(f"train_acc:{train_acc}")
 99         return train_loss,train_acc
100
101 def val(dataloader,model,loss_fn):
102     #验证模式
103     model.eval()
104     loss, current,n = 0.0, 0.0,0
105     with torch.no_grad():
106         val_bar = tqdm(dataloader, file=sys.stdout)
107         for batch, (x, y) in enumerate(val_bar):
108             # 前向传播
109             image, y = x.to(device), y.to(device)
110             output = model(image)
111             cur_loss = loss_fn(output, y)
112             _, pred = torch.max(output, axis=-1)
113             cur_acc = torch.sum(y == pred) / output.shape[0]
114             loss += cur_loss
115             current += cur_acc
116             n += 1
117             val_bar.desc = "val epoch[{}/{}] loss:{:.3f}".format(i + 1, epoch, cur_loss)
118         val_loss = loss / n
119         val_acc = current / n
120         print(f"val_loss:{val_loss}")
121         print(f"val_acc:{val_acc}")
122         return val_loss,val_acc
123
124 # 解决中文显示问题
125 plt.rcParams['font.sans-serif'] = ['SimHei']
126 plt.rcParams['axes.unicode_minus'] = False
127
128 #画图函数
129 def matplot_loss(train_loss,val_loss):
130     plt.figure()  # 声明一个新画布，这样两张图像的结果就不会出现重叠
131     plt.plot(train_loss,label='train_loss')#画图
132     plt.plot(val_loss, label='val_loss')
133     plt.legend(loc='best')#图例
134     plt.gca().xaxis.set_major_locator(MaxNLocator(integer=True))
135     plt.ylabel('loss',fontsize=12)
136     plt.xlabel('epoch',fontsize=12)
137     plt.title("训练集和验证集loss对比图")
138     folder = 'result'
139     if not os.path.exists(folder):
140         os.mkdir('result')
141     plt.savefig('result/loss.jpg')
142
143 def matplot_acc(train_acc,val_acc):
144     plt.figure()  # 声明一个新画布，这样两张图像的结果就不会出现重叠
145     plt.plot(train_acc, label='train_acc')  # 画图
146     plt.plot(val_acc, label='val_acc')
147     plt.legend(loc='best')  # 图例
148     plt.gca().xaxis.set_major_locator(MaxNLocator(integer=True))
149     plt.ylabel('acc', fontsize=12)
150     plt.xlabel('epoch', fontsize=12)
151     plt.title("训练集和验证集acc对比图")
152     plt.savefig('result/acc.jpg')
153
154 #开始训练
155 train_loss_list = []
156 val_loss_list = []
157 train_acc_list = []
158 val_acc_list = []
159
160 epoch = 20
161
162 max_acc = 0
163
164 for i in range(epoch):
165     lr_s.step()#学习率迭代，10epoch变为原来的0.1
166     train_loss,train_acc=train(train_dataloader,model,loss_fn,optimizer)
167     val_loss,val_acc=val(val_dataloader,model,loss_fn)
168
169     train_loss_list.append(train_loss)
170     train_acc_list.append(train_acc)
171     val_loss_list.append(val_loss)
172     val_acc_list.append(val_acc)
173     # 保存最好的模型权重
174     if val_acc > max_acc:
175         folder = 'save_model'
176         if not os.path.exists(folder):
177             os.mkdir('save_model')
178         max_acc = val_acc
179         print(f'save best model,第{i + 1}轮')
180         torch.save(model.state_dict(), 'save_model/best_model.pth')  # 保存网络权重
181     # 保存最后一轮
182     if i == epoch - 1:
183         torch.save(model.state_dict(), 'save_model/last_model.pth')  # 保存
184 print("done")
185
186 # 画图
187 matplot_loss(train_loss_list, val_loss_list)
188 matplot_acc(train_acc_list, val_acc_list)

train.py

训练结束后可以得到训练集和验证集的loss，acc对比图

简单的评估下：可以看到加载预训练权重后，即使只训练20轮，验证集的准确率高达90%多，这足以证明迁移学习的强大之处。

总结

VGG-16除了参数很多，需要较长的训练时间外，模型相比AlexNet还是进步挺大的

自己敲一下代码，会学到很多不懂的东西

最后，多看，多学，多试，总有一天你会称为大佬！