掌握PyTorch图片分类的简明教程

WpOh_rgznai100 2019-07-18 3207

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描述

1.引文

深度学习的比赛中，图片分类是很常见的比赛，同时也是很难取得特别高名次的比赛，因为图片分类已经被大家研究的很透彻，一些开源的网络很容易取得高分。如果大家还掌握不了使用开源的网络进行训练，再慢慢去模型调优，很难取得较好的成绩。

我们在[PyTorch小试牛刀]实战六·准备自己的数据集用于训练讲解了如何制作自己的数据集用于训练，这个教程在此基础上，进行训练与应用。

（实战六链接：

https://blog.csdn.net/xiaosongshine/article/details/85225873）

2.数据介绍

数据下载地址：

https://download.csdn.net/download/xiaosongshine/11128410

这次的实战使用的数据是交通标志数据集，共有62类交通标志。其中训练集数据有4572张照片（每个类别大概七十个），测试数据集有2520张照片（每个类别大概40个）。数据包含两个子目录分别train与test：

为什么还需要测试数据集呢？这个测试数据集不会拿来训练，是用来进行模型的评估与调优。

pytorch

train与test每个文件夹里又有62个子文件夹，每个类别在同一个文件夹内：

pytorch

我从中打开一个文件间，把里面图片展示出来：

pytorch

其中每张照片都类似下面的例子，100*100*3的大小。100是照片的照片的长和宽，3是什么呢？这其实是照片的色彩通道数目，RGB。彩色照片存储在计算机里就是以三维数组的形式。我们送入网络的也是这些数组。

3.网络构建

1.导入Python包，定义一些参数

1import torch as t 2import torchvision as tv 3import os 4import time 5import numpy as np 6from tqdm import tqdm 7 8 9class DefaultConfigs(object):1011 data_dir = "./traffic-sign/"12 data_list = ["train","test"]1314 lr = 0.00115 epochs = 1016 num_classes = 6217 image_size = 22418 batch_size = 4019 channels = 320 gpu = "0"21 train_len = 457222 test_len = 252023 use_gpu = t.cuda.is_available()2425config = DefaultConfigs()

2.数据准备，采用PyTorch提供的读取方式

注意一点Train数据需要进行随机裁剪，Test数据不要进行裁剪了

1normalize = tv.transforms.Normalize(mean = [0.485, 0.456, 0.406], 2 std = [0.229, 0.224, 0.225] 3 ) 4 5transform = { 6 config.data_list[0]:tv.transforms.Compose( 7 [tv.transforms.Resize([224,224]),tv.transforms.CenterCrop([224,224]), 8 tv.transforms.ToTensor(),normalize]#tv.transforms.Resize 用于重设图片大小 9 ) ,10 config.data_list[1]:tv.transforms.Compose(11 [tv.transforms.Resize([224,224]),tv.transforms.ToTensor(),normalize]12 ) 13}1415datasets = {16 x:tv.datasets.ImageFolder(root = os.path.join(config.data_dir,x),transform=transform[x])17 for x in config.data_list18}1920dataloader = {21 x:t.utils.data.DataLoader(dataset= datasets[x],22 batch_size=config.batch_size,23 shuffle=True24 ) 25 for x in config.data_list26}

3.构建网络模型（使用resnet18进行迁移学习，训练参数为最后一个全连接层 t.nn.Linear(512,num_classes)）

1def get_model(num_classes): 2 3 model = tv.models.resnet18(pretrained=True) 4 for parma in model.parameters(): 5 parma.requires_grad = False 6 model.fc = t.nn.Sequential( 7 t.nn.Dropout(p=0.3), 8 t.nn.Linear(512,num_classes) 9 )10 return(model)

如果电脑硬件支持，可以把下述代码屏蔽，则训练整个网络，最终准确率会上升，训练数据会变慢。

1for parma in model.parameters():2 parma.requires_grad = False

模型输出

1ResNet( 2 (conv1): Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False) 3 (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True) 4 (relu): ReLU(inplace) 5 (maxpool): MaxPool2d(kernel_size=3, stride=2, padding=1, dilation=1, ceil_mode=False) 6 (layer1): Sequential( 7 (0): BasicBlock( 8 (conv1): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False) 9 (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)10 (relu): ReLU(inplace)11 (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)12 (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)13 )14 (1): BasicBlock(15 (conv1): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)16 (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)17 (relu): ReLU(inplace)18 (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)19 (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)20 )21 )22 (layer2): Sequential(23 (0): BasicBlock(24 (conv1): Conv2d(64, 128, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)25 (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)26 (relu): ReLU(inplace)27 (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)28 (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)29 (downsample): Sequential(30 (0): Conv2d(64, 128, kernel_size=(1, 1), stride=(2, 2), bias=False)31 (1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)32 )33 )34 (1): BasicBlock(35 (conv1): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)36 (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)37 (relu): ReLU(inplace)38 (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)39 (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)40 )41 )42 (layer3): Sequential(43 (0): BasicBlock(44 (conv1): Conv2d(128, 256, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)45 (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)46 (relu): ReLU(inplace)47 (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)48 (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)49 (downsample): Sequential(50 (0): Conv2d(128, 256, kernel_size=(1, 1), stride=(2, 2), bias=False)51 (1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)52 )53 )54 (1): BasicBlock(55 (conv1): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)56 (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)57 (relu): ReLU(inplace)58 (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)59 (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)60 )61 )62 (layer4): Sequential(63 (0): BasicBlock(64 (conv1): Conv2d(256, 512, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)65 (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)66 (relu): ReLU(inplace)67 (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)68 (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)69 (downsample): Sequential(70 (0): Conv2d(256, 512, kernel_size=(1, 1), stride=(2, 2), bias=False)71 (1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)72 )73 )74 (1): BasicBlock(75 (conv1): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)76 (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)77 (relu): ReLU(inplace)78 (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)79 (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)80 )81 )82 (avgpool): AvgPool2d(kernel_size=7, stride=1, padding=0)83 (fc): Sequential(84 (0): Dropout(p=0.3)85 (1): Linear(in_features=512, out_features=62, bias=True)86 )87)

4.训练模型（支持自动GPU加速）

1def train(epochs): 2 3 model = get_model(config.num_classes) 4 print(model) 5 loss_f = t.nn.CrossEntropyLoss() 6 if(config.use_gpu): 7 model = model.cuda() 8 loss_f = loss_f.cuda() 910 opt = t.optim.Adam(model.fc.parameters(),lr = config.lr)11 time_start = time.time()1213 for epoch in range(epochs):14 train_loss = []15 train_acc = []16 test_loss = []17 test_acc = []18 model.train(True)19 print("Epoch {}/{}".format(epoch+1,epochs))20 for batch, datas in tqdm(enumerate(iter(dataloader["train"]))):21 x,y = datas22 if (config.use_gpu):23 x,y = x.cuda(),y.cuda()24 y_ = model(x)25 #print(x.shape,y.shape,y_.shape)26 _, pre_y_ = t.max(y_,1)27 pre_y = y28 #print(y_.shape)29 loss = loss_f(y_,pre_y)30 #print(y_.shape)31 acc = t.sum(pre_y_ == pre_y)3233 loss.backward()34 opt.step()35 opt.zero_grad()36 if(config.use_gpu):37 loss = loss.cpu()38 acc = acc.cpu()39 train_loss.append(loss.data)40 train_acc.append(acc)41 #if((batch+1)%5 ==0):42 time_end = time.time()43 print("Batch {}, Train loss:{:.4f}, Train acc:{:.4f}, Time: {}"\44 .format(batch+1,np.mean(train_loss)/config.batch_size,np.mean(train_acc)/config.batch_size,(time_end-time_start)))45 time_start = time.time()4647 model.train(False)48 for batch, datas in tqdm(enumerate(iter(dataloader["test"]))):49 x,y = datas50 if (config.use_gpu):51 x,y = x.cuda(),y.cuda()52 y_ = model(x)53 #print(x.shape,y.shape,y_.shape)54 _, pre_y_ = t.max(y_,1)55 pre_y = y56 #print(y_.shape)57 loss = loss_f(y_,pre_y)58 acc = t.sum(pre_y_ == pre_y)5960 if(config.use_gpu):61 loss = loss.cpu()62 acc = acc.cpu()6364 test_loss.append(loss.data)65 test_acc.append(acc)66 print("Batch {}, Test loss:{:.4f}, Test acc:{:.4f}".format(batch+1,np.mean(test_loss)/config.batch_size,np.mean(test_acc)/config.batch_size))6768 t.save(model,str(epoch+1)+"ttmodel.pkl")69707172if __name__ == "__main__":73 train(config.epochs)

训练结果如下：

1Epoch 1/10 2115it [00:48, 2.63it/s] 3Batch 115, Train loss:0.0590, Train acc:0.4635, Time: 48.985504150390625 463it [00:24, 2.62it/s] 5Batch 63, Test loss:0.0374, Test acc:0.6790, Time :24.648272275924683 6Epoch 2/10 7115it [00:45, 3.22it/s] 8Batch 115, Train loss:0.0271, Train acc:0.7576, Time: 45.68823838233948 963it [00:23, 2.62it/s]10Batch 63, Test loss:0.0255, Test acc:0.7524, Time :23.27178287506103511Epoch 3/1012115it [00:45, 3.19it/s]13Batch 115, Train loss:0.0181, Train acc:0.8300, Time: 45.926485061645511463it [00:23, 2.60it/s]15Batch 63, Test loss:0.0212, Test acc:0.7861, Time :23.8078927993774416Epoch 4/1017115it [00:45, 3.28it/s]18Batch 115, Train loss:0.0138, Train acc:0.8767, Time: 45.275250196456911963it [00:23, 2.57it/s]20Batch 63, Test loss:0.0173, Test acc:0.8385, Time :23.73632144927978521Epoch 5/1022115it [00:44, 3.22it/s]23Batch 115, Train loss:0.0112, Train acc:0.8950, Time: 44.9836382865905762463it [00:22, 2.69it/s]25Batch 63, Test loss:0.0156, Test acc:0.8520, Time :22.79007434844970726Epoch 6/1027115it [00:44, 3.19it/s]28Batch 115, Train loss:0.0095, Train acc:0.9159, Time: 45.104269504547122963it [00:22, 2.77it/s]30Batch 63, Test loss:0.0158, Test acc:0.8214, Time :22.8041245937347431Epoch 7/1032115it [00:45, 2.95it/s]33Batch 115, Train loss:0.0081, Train acc:0.9280, Time: 45.304390430450443463it [00:23, 2.66it/s]35Batch 63, Test loss:0.0139, Test acc:0.8528, Time :23.12237954139709536Epoch 8/1037115it [00:44, 3.23it/s]38Batch 115, Train loss:0.0073, Train acc:0.9300, Time: 44.3047628402709963963it [00:22, 2.74it/s]40Batch 63, Test loss:0.0142, Test acc:0.8496, Time :22.80183553695678741Epoch 9/1042115it [00:43, 3.19it/s]43Batch 115, Train loss:0.0068, Train acc:0.9361, Time: 44.084140300750734463it [00:23, 2.44it/s]45Batch 63, Test loss:0.0142, Test acc:0.8437, Time :23.60441923141479546Epoch 10/1047115it [00:46, 3.12it/s]48Batch 115, Train loss:0.0063, Train acc:0.9337, Time: 46.765970468521124963it [00:24, 2.65it/s]50Batch 63, Test loss:0.0130, Test acc:0.8591, Time :24.64351773262024

训练10个Epoch，测试集准确率可以到达0.86，已经达到不错效果。通过修改参数，增加训练，可以达到更高的准确率。

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