从零开始学Pytorch（十八）之kaggle图像分类
【摘要】
我们将运用在前面几节中学到的知识来参加Kaggle竞赛，该竞赛解决了CIFAR-10图像分类问题。比赛网址是https://www.kaggle.com/c/cifar-10.
import numpy as npimport torchimport torch.nn as nnimport torch.optim as optimi...
我们将运用在前面几节中学到的知识来参加Kaggle竞赛，该竞赛解决了CIFAR-10图像分类问题。比赛网址是https://www.kaggle.com/c/cifar-10.
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import numpy as np
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import torch
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import torch.nn as nn
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import torch.optim as optim
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import torchvision
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import torchvision.transforms as transforms
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import torch.nn.functional as F
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import torch.optim as optim
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from torchvision import datasets, transforms
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import os
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import time
获取和组织数据集
比赛数据分为训练集和测试集。训练集包含 50,000 图片。测试集包含 300,000 图片。两个数据集中的图像格式均为PNG，高度和宽度均为32像素，并具有三个颜色通道（RGB）。图像涵盖10个类别：飞机，汽车，鸟类，猫，鹿，狗，青蛙，马，船和卡车。 为了更容易上手，我们提供了上述数据集的小样本。“ train_tiny.zip”包含 80 训练样本，而“ test_tiny.zip”包含100个测试样本。它们的未压缩文件夹名称分别是“ train_tiny”和“ test_tiny”。
图像增强
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data_transform = transforms.Compose([
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transforms.Resize(40),
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transforms.RandomHorizontalFlip(),
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transforms.RandomCrop(32),
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transforms.ToTensor()
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])
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trainset = torchvision.datasets.ImageFolder(root='/home/kesci/input/CIFAR102891/cifar-10/train'
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, transform=data_transform)
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data = [d[0].data.cpu().numpy() for d in trainset]
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# 图像增强
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transform_train = transforms.Compose([
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transforms.RandomCrop(32, padding=4), #先四周填充0，再把图像随机裁剪成32*32
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transforms.RandomHorizontalFlip(), #图像一半的概率翻转，一半的概率不翻转
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transforms.ToTensor(),
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transforms.Normalize((0.4731, 0.4822, 0.4465), (0.2212, 0.1994, 0.2010)), #R,G,B每层的归一化用到的均值和方差
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])
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transform_test = transforms.Compose([
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transforms.ToTensor(),
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transforms.Normalize((0.4731, 0.4822, 0.4465), (0.2212, 0.1994, 0.2010)),
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])
导入数据集
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train_dir = '/home/kesci/input/CIFAR102891/cifar-10/train'
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test_dir = '/home/kesci/input/CIFAR102891/cifar-10/test'
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trainset = torchvision.datasets.ImageFolder(root=train_dir, transform=transform_train)
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trainloader = torch.utils.data.DataLoader(trainset, batch_size=256, shuffle=True)
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testset = torchvision.datasets.ImageFolder(root=test_dir, transform=transform_test)
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testloader = torch.utils.data.DataLoader(testset, batch_size=256, shuffle=False)
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classes = ['airplane', 'automobile', 'bird', 'cat', 'deer', 'dog', 'forg', 'horse', 'ship', 'truck']
定义模型
ResNet-18网络结构：ResNet全名Residual Network残差网络。Kaiming He 的《Deep Residual Learning for Image Recognition》获得了CVPR最佳论文。他提出的深度残差网络在2015年可以说是洗刷了图像方面的各大比赛，以绝对优势取得了多个比赛的冠军。而且它在保证网络精度的前提下，将网络的深度达到了152层，后来又进一步加到1000的深度。
Image Name
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class ResidualBlock(nn.Module): # 我们定义网络时一般是继承的torch.nn.Module创建新的子类
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def __init__(self, inchannel, outchannel, stride=1):
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super(ResidualBlock, self).__init__()
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#torch.nn.Sequential是一个Sequential容器，模块将按照构造函数中传递的顺序添加到模块中。
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self.left = nn.Sequential(
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nn.Conv2d(inchannel, outchannel, kernel_size=3, stride=stride, padding=1, bias=False),
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# 添加第一个卷积层,调用了nn里面的Conv2d（）
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nn.BatchNorm2d(outchannel), # 进行数据的归一化处理
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nn.ReLU(inplace=True), # 修正线性单元，是一种人工神经网络中常用的激活函数
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nn.Conv2d(outchannel, outchannel, kernel_size=3, stride=1, padding=1, bias=False),
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nn.BatchNorm2d(outchannel)
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)
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self.shortcut = nn.Sequential()
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if stride != 1 or inchannel != outchannel:
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self.shortcut = nn.Sequential(
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nn.Conv2d(inchannel, outchannel, kernel_size=1, stride=stride, bias=False),
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nn.BatchNorm2d(outchannel)
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)
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# 便于之后的联合,要判断Y = self.left(X)的形状是否与X相同
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def forward(self, x): # 将两个模块的特征进行结合，并使用ReLU激活函数得到最终的特征。
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out = self.left(x)
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out += self.shortcut(x)
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out = F.relu(out)
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return out
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class ResNet(nn.Module):
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def __init__(self, ResidualBlock, num_classes=10):
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super(ResNet, self).__init__()
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self.inchannel = 64
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self.conv1 = nn.Sequential( # 用3个3x3的卷积核代替7x7的卷积核，减少模型参数
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nn.Conv2d(3, 64, kernel_size=3, stride=1, padding=1, bias=False),
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nn.BatchNorm2d(64),
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nn.ReLU(),
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)
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self.layer1 = self.make_layer(ResidualBlock, 64, 2, stride=1)
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self.layer2 = self.make_layer(ResidualBlock, 128, 2, stride=2)
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self.layer3 = self.make_layer(ResidualBlock, 256, 2, stride=2)
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self.layer4 = self.make_layer(ResidualBlock, 512, 2, stride=2)
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self.fc = nn.Linear(512, num_classes)
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def make_layer(self, block, channels, num_blocks, stride):
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strides = [stride] + [1] * (num_blocks - 1) #第一个ResidualBlock的步幅由make_layer的函数参数stride指定
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# ，后续的num_blocks-1个ResidualBlock步幅是1
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layers = []
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for stride in strides:
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layers.append(block(self.inchannel, channels, stride))
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self.inchannel = channels
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return nn.Sequential(*layers)
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def forward(self, x):
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out = self.conv1(x)
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out = self.layer1(out)
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out = self.layer2(out)
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out = self.layer3(out)
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out = self.layer4(out)
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out = F.avg_pool2d(out, 4)
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out = out.view(out.size(0), -1)
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out = self.fc(out)
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return out
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def ResNet18():
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return ResNet(ResidualBlock)
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训练和测试
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# 定义是否使用GPU
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device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
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# 超参数设置
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EPOCH = 20 #遍历数据集次数
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pre_epoch = 0 # 定义已经遍历数据集的次数
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LR = 0.1 #学习率
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# 模型定义-ResNet
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net = ResNet18().to(device)
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# 定义损失函数和优化方式
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criterion = nn.CrossEntropyLoss() #损失函数为交叉熵，多用于多分类问题
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optimizer = optim.SGD(net.parameters(), lr=LR, momentum=0.9, weight_decay=5e-4)
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#优化方式为mini-batch momentum-SGD，并采用L2正则化（权重衰减）
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# 训练
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if __name__ == "__main__":
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print("Start Training, Resnet-18!")
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num_iters = 0
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for epoch in range(pre_epoch, EPOCH):
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print('\nEpoch: %d' % (epoch + 1))
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net.train()
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sum_loss = 0.0
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correct = 0.0
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total = 0
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for i, data in enumerate(trainloader, 0):
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#用于将一个可遍历的数据对象(如列表、元组或字符串)组合为一个索引序列，同时列出数据和数据下标，
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#下标起始位置为0，返回 enumerate(枚举) 对象。
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num_iters += 1
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inputs, labels = data
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inputs, labels = inputs.to(device), labels.to(device)
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optimizer.zero_grad() # 清空梯度
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# forward + backward
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outputs = net(inputs)
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loss = criterion(outputs, labels)
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loss.backward()
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optimizer.step()
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sum_loss += loss.item() * labels.size(0)
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_, predicted = torch.max(outputs, 1) #选出每一列中最大的值作为预测结果
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total += labels.size(0)
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correct += (predicted == labels).sum().item()
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# 每20个batch打印一次loss和准确率
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if (i + 1) % 20 == 0:
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print('[epoch:%d, iter:%d] Loss: %.03f | Acc: %.3f%% '
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% (epoch + 1, num_iters, sum_loss / (i + 1), 100. * correct / total))
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print("Training Finished, TotalEPOCH=%d" % EPOCH)
文章来源: blog.csdn.net，作者：小小谢先生，版权归原作者所有，如需转载，请联系作者。
原文链接：blog.csdn.net/xiewenrui1996/article/details/105131001
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