Pytorch实现Fashion-mnist分类任务全过程
作者：LGDDDDDD
这篇文章主要介绍了Pytorch实现Fashion-mnist分类任务全过程，具有很好的参考价值，希望对大家有所帮助。如有错误或未考虑完全的地方，望不吝赐教
数据概况
Fashion-mnist
经典的MNIST数据集包含了大量的手写数字。十几年来，来自机器学习、机器视觉、人工智能、深度学习领域的研究员们把这个数据集作为衡量算法的基准之一。
你会在很多的会议，期刊的论文中发现这个数据集的身影。实际上，MNIST数据集已经成为算法作者的必测的数据集之一。
类别标注
在Fashion-mnist数据集中，每个训练样本都按照以下类别进行了标注：
数据处理
对输入进行归一化
归一化时需要统一进行 x = (x - mean) / std
train_trans = transforms.Compose([
transforms.RandomCrop(28, padding=2),#数据增强
transforms.RandomHorizontalFlip(),
transforms.ToTensor(),
normalize
])
test_trans = transforms.Compose([
transforms.ToTensor(),
normalize
])
mnist_train = torchvision.datasets.FashionMNIST(root='../data',train=True,download=True,transform=train_trans)
mnist_test = torchvision.datasets.FashionMNIST(root='../data',train=False,download=True,transform=test_trans)
train_iter = torch.utils.data.DataLoader(mnist_train, batch_size=batch_size, shuffle=True)
test_iter = torch.utils.data.DataLoader(mnist_test, batch_size=batch_size, shuffle=False)
# 求整个数据集的均值
temp_sum = 0
cnt = 0
for X, y in train_iter:
if y.shape[0] != batch_size:
break # 最后一个batch不足batch_size,这里就忽略了
channel_mean = torch.mean(X, dim=(0,2,3)) # 按channel求均值(不过这里只有1个channel)
cnt += 1 # cnt记录的是batch的个数，不是图像
temp_sum += channel_mean[0].item()
dataset_global_mean = temp_sum / cnt
print('整个数据集的像素均值:{}'.format(dataset_global_mean))
# 求整个数据集的标准差
cnt = 0
temp_sum = 0
for X, y in train_iter:
if y.shape[0] != batch_size:
break # 最后一个batch不足batch_size,这里就忽略了
residual = (X - dataset_global_mean) ** 2
channel_var_mean = torch.mean(residual, dim=(0,2,3))
cnt += 1 # cnt记录的是batch的个数，不是图像
temp_sum += math.sqrt(channel_var_mean[0].item())
dataset_global_std = temp_sum / cnt
print('整个数据集的像素标准差:{}'.format(dataset_global_std))
整个数据集的像素均值:0.2860366729433025
整个数据集的像素标准差:0.35288708155778725
数据增强
加入随机裁剪和翻转
============================ step 1/6 数据 ============================
batch_size = 64
normalize = transforms.Normalize(mean=[0.286], std=[0.352])#对像素值归一化
train_trans = transforms.Compose([
transforms.RandomCrop(28, padding=2),
transforms.RandomHorizontalFlip(),
transforms.ToTensor(),
normalize
])
test_trans = transforms.Compose([
transforms.ToTensor(),
normalize
])
mnist_train = torchvision.datasets.FashionMNIST(root='../data',train=True,download=True,transform=train_trans)
mnist_test = torchvision.datasets.FashionMNIST(root='../data',train=False,download=True,transform=test_trans)
train_iter = torch.utils.data.DataLoader(mnist_train, batch_size=batch_size, shuffle=True)
test_iter = torch.utils.data.DataLoader(mnist_test, batch_size=batch_size, shuffle=False)
定义Resnet网络
class GlobalAvgPool2d(nn.Module):
"""
全局平均池化层
可通过将普通的平均池化的窗口形状设置成输入的高和宽实现
"""
def __init__(self):
super(GlobalAvgPool2d, self).__init__()
def forward(self, x):
return F.avg_pool2d(x, kernel_size=x.size()[2:])
class FlattenLayer(torch.nn.Module):
def __init__(self):
super(FlattenLayer, self).__init__()
def forward(self, x): # x shape: (batch, *, *, ...)
return x.view(x.shape[0], -1)
class Residual(nn.Module):
def __init__(self, in_channels, out_channels, use_1x1conv=False, stride=1):
"""
use_1×1conv: 是否使用额外的1x1卷积层来修改通道数
stride: 卷积层的步幅, resnet使用步长为2的卷积来替代pooling的作用，是个很赞的idea
"""
super(Residual, self).__init__()
self.conv1 = nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1, stride=stride)
self.conv2 = nn.Conv2d(out_channels, out_channels, kernel_size=3, padding=1)
if use_1x1conv:
self.conv3 = nn.Conv2d(in_channels, out_channels, kernel_size=1, stride=stride)
else:
self.conv3 = None
self.bn1 = nn.BatchNorm2d(out_channels)
self.bn2 = nn.BatchNorm2d(out_channels)
def forward(self, X):
Y = F.relu(self.bn1(self.conv1(X)))
Y = self.bn2(self.conv2(Y))
if self.conv3:
X = self.conv3(X)
return F.relu(Y + X)
def resnet_block(in_channels, out_channels, num_residuals, first_block=False):
'''
resnet block
num_residuals: 当前block包含多少个残差块
first_block: 是否为第一个block
一个resnet block由num_residuals个残差块组成
其中第一个残差块起到了通道数的转换和pooling的作用
后面的若干残差块就是完成正常的特征提取
'''
if first_block:
assert in_channels == out_channels # 第一个模块的输出通道数同输入通道数一致
blk = []
for i in range(num_residuals):
if i == 0 and not first_block:
blk.append(Residual(in_channels, out_channels, use_1x1conv=True, stride=2))
else:
blk.append(Residual(out_channels, out_channels))
return nn.Sequential(*blk)
# 定义resnet模型结构
net = nn.Sequential(
nn.Conv2d(1, 32, kernel_size=3, stride=1, padding=1), # TODO: 缩小感受野, 缩channel
nn.BatchNorm2d(32),
nn.ReLU())
# nn.ReLU(),
# nn.MaxPool2d(kernel_size=2, stride=2)) # TODO：去掉maxpool缩小感受野
# 然后是连续4个block
net.add_module("resnet_block1", resnet_block(32, 32, 2, first_block=True)) # TODO: channel统一减半
net.add_module("resnet_block2", resnet_block(32, 64, 2))
net.add_module("resnet_block3", resnet_block(64, 128, 2))
net.add_module("resnet_block4", resnet_block(128, 256, 2))
# global average pooling
net.add_module("global_avg_pool", GlobalAvgPool2d())
# fc layer
net.add_module("fc", nn.Sequential(FlattenLayer(), nn.Linear(256, 10)))
训练与测试
def evaluate_accuracy(data_iter, net, device=None):
#评估模型在测试集的准确率
if device is None and isinstance(net, torch.nn.Module):
# 如果没指定device就使用net的device
device = list(net.parameters())[0].device
net.eval()
acc_sum, n = 0.0, 0
with torch.no_grad():
for X, y in data_iter:
acc_sum += (net(X.to(device)).argmax(dim=1) == y.to(device)).float().sum().cpu().item()
n += y.shape[0]
net.train() # 改回训练模式
return acc_sum / n
def train_model(net, train_iter, test_iter, batch_size, optimizer, device, num_epochs):
net = net.to(device)
print("training on ", device)
loss = torch.nn.CrossEntropyLoss()
best_test_acc = 0
for epoch in range(num_epochs):
train_l_sum, train_acc_sum, n, batch_count, start = 0.0, 0.0, 0, 0, time.time()
for X, y in train_iter:
X = X.to(device)
y = y.to(device)
y_hat = net(X)
l = loss(y_hat, y)
optimizer.zero_grad()
l.backward()
optimizer.step()
train_l_sum += l.cpu().item()
train_acc_sum += (y_hat.argmax(dim=1) == y).sum().cpu().item()
n += y.shape[0]
batch_count += 1
test_acc = evaluate_accuracy(test_iter, net)
print('epoch %d, loss %.4f, train acc %.3f, test acc %.3f, time %.1f sec'
% (epoch + 1, train_l_sum / batch_count, train_acc_sum / n, test_acc, time.time() - start))
if test_acc > best_test_acc:
print('find best! save at model/best.pth')
best_test_acc = test_acc
torch.save(net.state_dict(), 'model/best.pth')
lr, num_epochs = 0.01, 10
optimizer = torch.optim.Adam(net.parameters(), lr=lr)
device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')
train_model(net, train_iter, test_iter, batch_size, optimizer, device, num_epochs)
完整代码
import os
import sys
import time
import torch
from torch import nn, optim
import torch.nn.functional as F
import torchvision
from torchvision import transforms
class GlobalAvgPool2d(nn.Module):
"""
全局平均池化层
可通过将普通的平均池化的窗口形状设置成输入的高和宽实现
"""
def __init__(self):
super(GlobalAvgPool2d, self).__init__()
def forward(self, x):
return F.avg_pool2d(x, kernel_size=x.size()[2:])
class FlattenLayer(torch.nn.Module):
def __init__(self):
super(FlattenLayer, self).__init__()
def forward(self, x): # x shape: (batch, *, *, ...)
return x.view(x.shape[0], -1)
class Residual(nn.Module):
def __init__(self, in_channels, out_channels, use_1x1conv=False, stride=1):
"""
use_1×1conv: 是否使用额外的1x1卷积层来修改通道数
stride: 卷积层的步幅, resnet使用步长为2的卷积来替代pooling的作用，是个很赞的idea
"""
super(Residual, self).__init__()
self.conv1 = nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1, stride=stride)
self.conv2 = nn.Conv2d(out_channels, out_channels, kernel_size=3, padding=1)
if use_1x1conv:
self.conv3 = nn.Conv2d(in_channels, out_channels, kernel_size=1, stride=stride)
else:
self.conv3 = None
self.bn1 = nn.BatchNorm2d(out_channels)
self.bn2 = nn.BatchNorm2d(out_channels)
def forward(self, X):
Y = F.relu(self.bn1(self.conv1(X)))
Y = self.bn2(self.conv2(Y))
if self.conv3:
X = self.conv3(X)
return F.relu(Y + X)
def resnet_block(in_channels, out_channels, num_residuals, first_block=False):
'''
resnet block
num_residuals: 当前block包含多少个残差块
first_block: 是否为第一个block
一个resnet block由num_residuals个残差块组成
其中第一个残差块起到了通道数的转换和pooling的作用
后面的若干残差块就是完成正常的特征提取
'''
if first_block:
assert in_channels == out_channels # 第一个模块的输出通道数同输入通道数一致
blk = []
for i in range(num_residuals):
if i == 0 and not first_block:
blk.append(Residual(in_channels, out_channels, use_1x1conv=True, stride=2))
else:
blk.append(Residual(out_channels, out_channels))
return nn.Sequential(*blk)
# 定义resnet模型结构
net = nn.Sequential(
nn.Conv2d(1, 32, kernel_size=3, stride=1, padding=1), # TODO: 缩小感受野, 缩channel
nn.BatchNorm2d(32),
nn.ReLU())
# nn.ReLU(),
# nn.MaxPool2d(kernel_size=2, stride=2)) # TODO：去掉maxpool缩小感受野
# 然后是连续4个block
net.add_module("resnet_block1", resnet_block(32, 32, 2, first_block=True)) # TODO: channel统一减半
net.add_module("resnet_block2", resnet_block(32, 64, 2))
net.add_module("resnet_block3", resnet_block(64, 128, 2))
net.add_module("resnet_block4", resnet_block(128, 256, 2))
# global average pooling
net.add_module("global_avg_pool", GlobalAvgPool2d())
# fc layer
net.add_module("fc", nn.Sequential(FlattenLayer(), nn.Linear(256, 10)))
def load_data_fashion_mnist(batch_size, root='../data'):
"""Download the fashion mnist dataset and then load into memory."""
normalize = transforms.Normalize(mean=[0.28], std=[0.35])
train_augs = transforms.Compose([
transforms.RandomCrop(28, padding=2),
transforms.RandomHorizontalFlip(),
transforms.ToTensor(),
normalize
])
test_augs = transforms.Compose([
transforms.ToTensor(),
normalize
])
mnist_train = torchvision.datasets.FashionMNIST(root=root, train=True, download=True, transform=train_augs)
mnist_test = torchvision.datasets.FashionMNIST(root=root, train=False, download=True, transform=test_augs)
if sys.platform.startswith('win'):
num_workers = 0 # 0表示不用额外的进程来加速读取数据
else:
num_workers = 4
train_iter = torch.utils.data.DataLoader(mnist_train, batch_size=batch_size, shuffle=True, num_workers=num_workers)
test_iter = torch.utils.data.DataLoader(mnist_test, batch_size=batch_size, shuffle=False, num_workers=num_workers)
return train_iter, test_iter
print('训练...')
batch_size = 64
train_iter, test_iter = load_data_fashion_mnist(batch_size, root='../data')
def evaluate_accuracy(data_iter, net, device=None):
if device is None and isinstance(net, torch.nn.Module):
# 如果没指定device就使用net的device
device = list(net.parameters())[0].device
net.eval()
acc_sum, n = 0.0, 0
with torch.no_grad():
for X, y in data_iter:
acc_sum += (net(X.to(device)).argmax(dim=1) == y.to(device)).float().sum().cpu().item()
n += y.shape[0]
net.train() # 改回训练模式
return acc_sum / n
def train_model(net, train_iter, test_iter, batch_size, optimizer, device, num_epochs, lr, lr_period, lr_decay):
net = net.to(device)
print("training on ", device)
loss = torch.nn.CrossEntropyLoss()
best_test_acc = 0
for epoch in range(num_epochs):
train_l_sum, train_acc_sum, n, batch_count, start = 0.0, 0.0, 0, 0, time.time()
if epoch > 0 and epoch % lr_period == 0: # 每lr_period个epoch，学习率衰减一次
lr = lr * lr_decay
for param_group in optimizer.param_groups:
param_group['lr'] = lr
for X, y in train_iter:
X = X.to(device)
y = y.to(device)
y_hat = net(X)
l = loss(y_hat, y)
optimizer.zero_grad()
l.backward()
optimizer.step()
train_l_sum += l.cpu().item()
train_acc_sum += (y_hat.argmax(dim=1) == y).sum().cpu().item()
n += y.shape[0]
batch_count += 1
test_acc = evaluate_accuracy(test_iter, net)
print('epoch %d, loss %.4f, train acc %.3f, test acc %.3f, time %.1f sec'
% (epoch + 1, train_l_sum / batch_count, train_acc_sum / n, test_acc, time.time() - start))
if test_acc > best_test_acc:
print('find best! save at model/best.pth')
best_test_acc = test_acc
torch.save(net.state_dict(), 'model/best.pth')
# utils.save_model({
# 'arch': args.model,
# 'state_dict': net.state_dict()
# }, 'saved-models/{}-run-{}.pth.tar'.format(args.model, run))
lr, num_epochs, lr_period, lr_decay = 0.01, 50, 5, 0.1
#optimizer = optim.Adam(net.parameters(), lr=lr)
optimizer = optim.SGD(net.parameters(), lr=lr, momentum=0.9, weight_decay=5e-4)
device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')
train_model(net, train_iter, test_iter, batch_size, optimizer, device, num_epochs, lr, lr_period, lr_decay)
print('加载最优模型')
net.load_state_dict(torch.load('model/best.pth'))
net = net.to(device)
print('inference测试集')
net.eval()
id = 0
preds_list = []
with torch.no_grad():
for X, y in test_iter:
batch_pred = list(net(X.to(device)).argmax(dim=1).cpu().numpy())
for y_pred in batch_pred:
preds_list.append((id, y_pred))
id += 1
print('生成测试集评估文件')
with open('result.csv', 'w') as f:
f.write('ID,Prediction\n')
for id, pred in preds_list:
f.write('{},{}\n'.format(id, pred))
总结
以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。