深度学习基础--ResNet网络的讲解，ResNet50的复现(pytorch)以及用复现的ResNet50做鸟类图像分类

• 🍨 本文为🔗365天深度学习训练营 中的学习记录博客
• 🍖 原作者：K同学啊

前言

• 如果说最经典的神经网络，ResNet肯定是一个，这篇文章是本人学习ResNet的学习笔记，并且用pytorch复现了ResNet50，后面用它做了一个鸟类图像分类demo；
• 欢迎收藏 + 关注，本人将会持续更新

文章目录

• ResNet网络讲解
• • 什么是ResNet？
  • ResNet神经网络突出点
  • 为什么采用残差连接
  • • 模型退化、梯度消失、梯度爆炸
    • 解决方法
  • 残差网络
• ResNet-50复现
• • 1、导入数据
  • • 1、导入库
    • 2、查看数据信息和导入数据
    • 3、展示数据
    • 4、数据导入
    • 5、数据划分
    • 6、动态加载数据
  • 2、构建ResNet-50网络
  • 3、模型训练
  • • 1、构建训练集
    • 2、构建测试集
    • 3、设置超参数
  • 4、模型训练
  • 5、结果可视化
• 参考资料

ResNet网络讲解

什么是ResNet？

ResNet网络是CNN的经典网络架构，是有大神何凯明提出的，主要为了解决随着网络的加深而引起的“ 退化 ”问题，主要用于图像分类。

可以说在如今的CV领域里面，大部分网络结构都有参考ResNet网络思想，无论是在图像分类、目标检测、图像识别上，甚至在Transformer网络模型中，也融合了ResNet网络的思想。

ResNet神经网络突出点

• 网络结构超过1000层：
  • ❔ ❔ 超过1000层网络结构不是很容易么？ 小编在学习深度学习的时候，曾经遇到过这样一个问题，有时候加深网络结构，反而在准确率、损失率上更差，这种现象称为模型“ 退化 ”现象，而ResNet的残差连接可以保证下一层的输出不会比输入差，从而可以加深网络结构。
• 提出残差模块(residual)：这个是ResNet的核心；
• 采用大量的归一化在卷积层与激活函数之间.

为什么采用残差连接

模型退化、梯度消失、梯度爆炸

• 👉 模型退化：指随着网络层数的加深，其效果出现下降趋势，不如层数少的情况。如论文中图示，56层效果不如20层效果；

• 👉 梯度消失：这个是指随着网络层数的增加，反向传播，梯度更新的时候可能会造成前面几层的梯度很小、接近于0，这就会导致权重的更新会特别慢，效率低下。
• 👉 梯度爆炸：指随着网络层数的增加，在反向传播的时候，梯度变得非常大，从而在更新权重的时候，权重值发生大幅度变化，这可能导致网络不稳定，甚至是无法收敛。

解决方法

• 梯度消失、梯度爆炸：在数据预处理和网络层之间加入：BN层(Batch Normalization)，从而对数据进行归一化；
• 模型退化：采用残差连接，如论文图，随着网络层数的增加，损失率更低了。

残差网络

在讲述前，这里先讲述一下恒等映射的概念：

• 恒等映射核心是复制，就是复制网络层，什么也不干。

➿ 可以这么理解：假设在一种网络A的后面添加几层形成新的网络B，如果A的输出经过新的层级变成B的输出没有发送变化，那么就可以说网络A和网络B的错误率是相等的，这样就确保了加深的网络层不会比之前的网络层效果差。

resent网络说明了，更深的网络结构可以有更好的效果，而解决这个的核心就是残差连接，网络结果如图所示：

上图就是何凯明提出的残差结构，这种结构实现了恒等映射，网络层的输出由两大模块组成：

• 其一：正常的卷积层；
• 其二：有一个分支输出到连接上，这个输出值就是输入的值；

最终结果就是：卷积层输出+分支输出，数学公式如下：

其中F(x)是卷积层的输出，x是分支的输入值。

极端情况：F(x)的网络层中，所有参数都为0，那么H(x)就是恒等映射。这样就确保了最后的错误率不会因为网络层的增加而导致变大。

在ResNet中有两个不同的ResNet模块，如图所示：

左边：

• 有两层残差单元，输出通道都是3*3
• 使用情况：用于较浅的ResNet网络。

右边：

• 三层残差单元，称为blottlenck模块，作用是：现用1*1卷积进行降维，后用3*3卷积进行特征特权，最后用1*1卷积恢复原来的维度，这个可以很好的减少参数个数，用于较深的神经网络。

下图参考一个csdn大神笔记图：

CNN参数计算公式：卷积核尺寸 * 卷积核速度 * 卷积核组数 == 卷积核尺寸 * 输入特征矩阵深度 * 输出矩阵深度。

ResNet经典的网络结构有ResNet-50，ResNet-101等，本文将用pytorch复现ResNet-50，并用其做一个简单的实验–鸟类图片分类。

ResNet-50网络结果如下：

ResNet-50复现

1、导入数据

1、导入库

import torch  
import torch.nn as nn
import torchvision 
import numpy as np 
import os, PIL, pathlib 

# 设置设备
device = "cuda" if torch.cuda.is_available() else "cpu"

device 

'cuda'

2、查看数据信息和导入数据

数据目录有两个文件：一个数据文件，一个权重。

data_dir = "./data/bird_photos"

data_dir = pathlib.Path(data_dir)

# 类别数量
classnames = [str(path).split('/')[0] for path in os.listdir(data_dir)]

classnames

['Bananaquit', 'Black Skimmer', 'Black Throated Bushtiti', 'Cockatoo']

3、展示数据

import matplotlib.pylab as plt  
from PIL import Image 

# 获取文件名称
data_path_name = "./data/bird_photos/Bananaquit/"
data_path_list = [f for f in os.listdir(data_path_name) if f.endswith(('jpg', 'png'))]

# 创建画板
fig, axes = plt.subplots(2, 8, figsize=(16, 6))

for ax, img_file in zip(axes.flat, data_path_list):
    path_name = os.path.join(data_path_name, img_file)
    img = Image.open(path_name) # 打开
    # 显示
    ax.imshow(img)
    ax.axis('off')
    
plt.show()

​

​

4、数据导入

from torchvision import transforms, datasets 

# 数据统一格式
img_height = 224
img_width = 224 

data_tranforms = transforms.Compose([
    transforms.Resize([img_height, img_width]),
    transforms.ToTensor(),
    transforms.Normalize(   # 归一化
        mean=[0.485, 0.456, 0.406],
        std=[0.229, 0.224, 0.225] 
    )
])

# 加载所有数据
total_data = datasets.ImageFolder(root="./data/bird_photos", transform=data_tranforms)

5、数据划分

# 大小 8 : 2
train_size = int(len(total_data) * 0.8)
test_size = len(total_data) - train_size 

train_data, test_data = torch.utils.data.random_split(total_data, [train_size, test_size])

6、动态加载数据

batch_size = 32 

train_dl = torch.utils.data.DataLoader(
    train_data,
    batch_size=batch_size,
    shuffle=True
)

test_dl = torch.utils.data.DataLoader(
    test_data,
    batch_size=batch_size,
    shuffle=False
)

# 查看数据维度
for data, labels in train_dl:
    print("data shape[N, C, H, W]: ", data.shape)
    print("labels: ", labels)
    break

data shape[N, C, H, W]:  torch.Size([32, 3, 224, 224])
labels:  tensor([0, 1, 0, 1, 2, 1, 1, 0, 2, 2, 1, 2, 1, 3, 1, 2, 2, 2, 2, 1, 2, 1, 2, 2,
        0, 3, 3, 3, 3, 2, 3, 3])

2、构建ResNet-50网络

import torch.nn.functional as F

# 定义残差模块一，这个用于处理输入和输出通道一样的情况
'''  
卷积核大小：1       3       1
核心特点：
    尺寸不变：输入和输出的尺寸保持一致。 
    没有下采样：没有使用步长大于1的卷积操作，因此没有改变特征图的空间尺寸
'''
class Identity_block(nn.Module):
    def __init__(self, in_channels, kernel_size, filters):
        super(Identity_block, self).__init__()
        
        # 输出通道
        filter1, filter2, filter3 = filters
        
        # 卷积层一
        self.conv1 = nn.Conv2d(in_channels, filter1, kernel_size=1, stride=1)
        self.bn1 = nn.BatchNorm2d(filter1)
        
        # 卷积层2
        self.conv2 = nn.Conv2d(filter1, filter2, kernel_size=kernel_size, padding=1)   # 通过卷积输入输出公式发现，padding=1，可以保证输入和输出尺寸相同
        self.bn2 = nn.BatchNorm2d(filter2)
        
        # 卷积层3
        self.conv3 = nn.Conv2d(filter2, filter3, kernel_size=1, stride=1)
        self.bn3 = nn.BatchNorm2d(filter3)
        
    def forward(self, x):
        # 记录原始值
        xx = x
        x = F.relu(self.bn1(self.conv1(x)))
        x = F.relu(self.bn2(self.conv2(x)))
        x = self.bn3(self.conv3(x))
        # 残差连接，输入、输出维度不变
        x += xx
        x = F.relu(x)
        
        return x 
    
# 定义卷积模块二：用于处理输入和输出不一样的情况
'''  
* 卷积核还是：1 3 1
* stride=2
* 这里的分支是采用一个Conv2D，和一个归一化BN层，也是为了处理数据维度吧, 这种维度的变化，可以用ai举例子

核心特点：
    尺寸变化，stride=2降维
'''
class ConvBlock(nn.Module):
    def __init__(self, in_channels, kernel_size, filters, stride=2):
        super(ConvBlock, self).__init__()
        
        filter1, filter2, filter3= filters
        
        # 卷积层1
        self.conv1 = nn.Conv2d(in_channels, filter1, kernel_size=1, stride=stride)
        self.bn1 = nn.BatchNorm2d(filter1)
        
        # 卷积2
        self.conv2 = nn.Conv2d(filter1, filter2, kernel_size=kernel_size, padding=1) # 需要维持维度不变
        self.bn2 = nn.BatchNorm2d(filter2)
        
        # 卷积3
        self.conv3 = nn.Conv2d(filter2, filter3, kernel_size=1, stride=1)  # stride = 1，维持通道不变
        self.bn3 = nn.BatchNorm2d(filter3)
        
        # 用于匹配维度的shortcut卷积，这个就是上面Identity_block的x分支
        self.shortcut = nn.Conv2d(in_channels, filter3, kernel_size=1, stride=stride)
        self.shortcut_bn = nn.BatchNorm2d(filter3)
        
    def forward(self, x):
        xx = x
        x = F.relu(self.bn1(self.conv1(x)))
        x = F.relu(self.bn2(self.conv2(x)))
        x = self.bn3(self.conv3(x))
        
        temp = self.shortcut_bn(self.shortcut(xx))
        
        x += temp
        
        x = F.relu(x)
        
        return x 
        
# 定义ResNet50
class ResNet50(nn.Module):
    def __init__(self, classes):   # 类别数量
        super().__init__()
        
        # 头顶
        self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3)
        self.bn1 = nn.BatchNorm2d(64)
        self.max_pool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
        
        # 第一部分
        self.part1_1 = ConvBlock(64, 3, [64, 64, 256], stride=1)
        self.part1_2 = Identity_block(256, 3, [64, 64, 256])
        self.part1_3 = Identity_block(256, 3, [64, 64, 256])
        
        # 第二部分
        self.part2_1 = ConvBlock(256, 3, [128, 128, 512])
        self.part2_2 = Identity_block(512, 3, [128, 128, 512])
        self.part2_3 = Identity_block(512, 3, [128, 128, 512])
        self.part2_4 = Identity_block(512, 3, [128, 128, 512])
        
        # 第三部分
        self.part3_1 = ConvBlock(512, 3, [256, 256, 1024])
        self.part3_2 = Identity_block(1024, 3, [256, 256, 1024])
        self.part3_3 = Identity_block(1024, 3, [256, 256, 1024])
        self.part3_4 = Identity_block(1024, 3, [256, 256, 1024])
        self.part3_5 = Identity_block(1024, 3, [256, 256, 1024])
        self.part3_6 = Identity_block(1024, 3, [256, 256, 1024])
        
        # 第四部分
        self.part4_1 = ConvBlock(1024, 3, [512, 512, 2048])
        self.part4_2 = Identity_block(2048, 3, [512, 512, 2048])
        self.part4_3 = Identity_block(2048, 3, [512, 512, 2048])
        
        # 平均池化
        self.avg_pool = nn.AvgPool2d(kernel_size=7)
        
        # 全连接
        self.fn1 = nn.Linear(2048, classes)
        
    def forward(self, x):
        # 头部
        x = F.relu(self.bn1(self.conv1(x)))
        x = self.max_pool(x)
        
        x = self.part1_1(x)
        x = self.part1_2(x)
        x = self.part1_3(x)
        
        x = self.part2_1(x)
        x = self.part2_2(x)
        x = self.part2_3(x)
        x = self.part2_4(x)
        
        x = self.part3_1(x)
        x = self.part3_2(x)
        x = self.part3_3(x)
        x = self.part3_4(x)
        x = self.part3_5(x)
        x = self.part3_6(x)
        
        x = self.part4_1(x)
        x = self.part4_2(x)
        x = self.part4_3(x)
        
        x = self.avg_pool(x)
        
        x = x.view(x.size(0), -1)  # 扁平化
        x = self.fn1(x)
        
        return x 
        
model = ResNet50(classes=len(classnames)).to(device)

model

ResNet50(
  (conv1): Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3))
  (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  (max_pool): MaxPool2d(kernel_size=3, stride=2, padding=1, dilation=1, ceil_mode=False)
  (part1_1): ConvBlock(
    (conv1): Conv2d(64, 64, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(64, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (shortcut): Conv2d(64, 256, kernel_size=(1, 1), stride=(1, 1))
    (shortcut_bn): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part1_2): Identity_block(
    (conv1): Conv2d(256, 64, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(64, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part1_3): Identity_block(
    (conv1): Conv2d(256, 64, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(64, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part2_1): ConvBlock(
    (conv1): Conv2d(256, 128, kernel_size=(1, 1), stride=(2, 2))
    (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(128, 512, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (shortcut): Conv2d(256, 512, kernel_size=(1, 1), stride=(2, 2))
    (shortcut_bn): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part2_2): Identity_block(
    (conv1): Conv2d(512, 128, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(128, 512, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part2_3): Identity_block(
    (conv1): Conv2d(512, 128, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(128, 512, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part2_4): Identity_block(
    (conv1): Conv2d(512, 128, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(128, 512, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part3_1): ConvBlock(
    (conv1): Conv2d(512, 256, kernel_size=(1, 1), stride=(2, 2))
    (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(256, 1024, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (shortcut): Conv2d(512, 1024, kernel_size=(1, 1), stride=(2, 2))
    (shortcut_bn): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part3_2): Identity_block(
    (conv1): Conv2d(1024, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(256, 1024, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part3_3): Identity_block(
    (conv1): Conv2d(1024, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(256, 1024, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part3_4): Identity_block(
    (conv1): Conv2d(1024, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(256, 1024, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part3_5): Identity_block(
    (conv1): Conv2d(1024, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(256, 1024, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part3_6): Identity_block(
    (conv1): Conv2d(1024, 256, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(256, 1024, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part4_1): ConvBlock(
    (conv1): Conv2d(1024, 512, kernel_size=(1, 1), stride=(2, 2))
    (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(512, 2048, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (shortcut): Conv2d(1024, 2048, kernel_size=(1, 1), stride=(2, 2))
    (shortcut_bn): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part4_2): Identity_block(
    (conv1): Conv2d(2048, 512, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(512, 2048, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (part4_3): Identity_block(
    (conv1): Conv2d(2048, 512, kernel_size=(1, 1), stride=(1, 1))
    (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (conv3): Conv2d(512, 2048, kernel_size=(1, 1), stride=(1, 1))
    (bn3): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  )
  (avg_pool): AvgPool2d(kernel_size=7, stride=7, padding=0)
  (fn1): Linear(in_features=2048, out_features=4, bias=True)
)

model(torch.randn(32, 3, 224, 224).to(device)).shape

torch.Size([32, 4])

3、模型训练

1、构建训练集

def train(dataloader, model, loss_fn, optimizer):
    size = len(dataloader.dataset)
    batch_size = len(dataloader)
    
    train_acc, train_loss = 0, 0 
    
    for X, y in dataloader:
        X, y = X.to(device), y.to(device)
        
        # 训练
        pred = model(X)
        loss = loss_fn(pred, y)
        
        # 梯度下降法
        optimizer.zero_grad()
        loss.backward()
        optimizer.step()
        
        # 记录
        train_loss += loss.item()
        train_acc += (pred.argmax(1) == y).type(torch.float).sum().item()
        
    train_acc /= size
    train_loss /= batch_size
    
    return train_acc, train_loss

2、构建测试集

def test(dataloader, model, loss_fn):
    size = len(dataloader.dataset)
    batch_size = len(dataloader)
    
    test_acc, test_loss = 0, 0 
    
    with torch.no_grad():
        for X, y in dataloader:
            X, y = X.to(device), y.to(device)
        
            pred = model(X)
            loss = loss_fn(pred, y)
        
            test_loss += loss.item()
            test_acc += (pred.argmax(1) == y).type(torch.float).sum().item()
        
    test_acc /= size
    test_loss /= batch_size
    
    return test_acc, test_loss

3、设置超参数

loss_fn = nn.CrossEntropyLoss()  # 损失函数     
learn_lr = 1e-4             # 超参数
optimizer = torch.optim.Adam(model.parameters(), lr=learn_lr)   # 优化器

4、模型训练

train_acc = []
train_loss = []
test_acc = []
test_loss = []

epoches = 80

for i in range(epoches):
    model.train()
    epoch_train_acc, epoch_train_loss = train(train_dl, model, loss_fn, optimizer)
    
    model.eval()
    epoch_test_acc, epoch_test_loss = test(test_dl, model, loss_fn)
    
    train_acc.append(epoch_train_acc)
    train_loss.append(epoch_train_loss)
    test_acc.append(epoch_test_acc)
    test_loss.append(epoch_test_loss)
    
    # 输出
    template = ('Epoch:{:2d}, Train_acc:{:.1f}%, Train_loss:{:.3f}, Test_acc:{:.1f}%, Test_loss:{:.3f}')
    print(template.format(i + 1, epoch_train_acc*100, epoch_train_loss, epoch_test_acc*100, epoch_test_loss))
    
print("Done")

5、结果可视化

import matplotlib.pyplot as plt
#隐藏警告
import warnings
warnings.filterwarnings("ignore")               #忽略警告信息

epochs_range = range(epoches)

plt.figure(figsize=(12, 3))
plt.subplot(1, 2, 1)

plt.plot(epochs_range, train_acc, label='Training Accuracy')
plt.plot(epochs_range, test_acc, label='Test Accuracy')
plt.legend(loc='lower right')
plt.title('Training Accuracy')

plt.subplot(1, 2, 2)
plt.plot(epochs_range, train_loss, label='Training Loss')
plt.plot(epochs_range, test_loss, label='Test Loss')
plt.legend(loc='upper right')
plt.title('Training= Loss')
plt.show()

​

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参考资料

【深度学习】ResNet网络讲解-CSDN博客

K同学啊，训练营文档