[深度应用]·实战掌握PyTorch图片分类简明教程

[深度应用]·实战掌握PyTorch图片分类简明教程

个人网站--> http://www.yansongsong.cn/

项目GitHub地址--> https://github.com/xiaosongshine/image_classifier_PyTorch/

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。

2.数据介绍

数据 下载地址

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。

​

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：

​

我从中打开一个文件间，把里面图片展示出来：

​

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

import torch as t
import torchvision as tv
import os
import time
import numpy as np
from tqdm import tqdm

class DefaultConfigs(object):

    data_dir = "./traffic-sign/"
    data_list = ["train","test"]

    lr = 0.001
    epochs = 10
    num_classes = 62
    image_size = 224
    batch_size = 40
    channels = 3
    gpu = "0"
    train_len = 4572
    test_len = 2520
    use_gpu = t.cuda.is_available()

config = DefaultConfigs()

　　

2.数据准备，采用PyTorch提供的读取方式（具体内容参考[PyTorch小试牛刀]实战六·准备自己的数据集用于训练）

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

normalize = tv.transforms.Normalize(mean = [0.485, 0.456, 0.406],
                                    std = [0.229, 0.224, 0.225]
                                    )

transform = {
    config.data_list[0]:tv.transforms.Compose(
        [tv.transforms.Resize([224,224]),tv.transforms.CenterCrop([224,224]),
        tv.transforms.ToTensor(),normalize]#tv.transforms.Resize 用于重设图片大小
    ) ,
    config.data_list[1]:tv.transforms.Compose(
        [tv.transforms.Resize([224,224]),tv.transforms.ToTensor(),normalize]
    )
}

datasets = {
    x:tv.datasets.ImageFolder(root = os.path.join(config.data_dir,x),transform=transform[x])
    for x in config.data_list
}

dataloader = {
    x:t.utils.data.DataLoader(dataset= datasets[x],
        batch_size=config.batch_size,
        shuffle=True
    )
    for x in config.data_list
}

　　

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)） 

def get_model(num_classes):

    model = tv.models.resnet18(pretrained=True)
    for parma in model.parameters():
        parma.requires_grad = False
    model.fc = t.nn.Sequential(
        t.nn.Dropout(p=0.3),
        t.nn.Linear(512,num_classes)
    )
    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。

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

　　

模型输出

ResNet(
  (conv1): Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)
  (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
  (relu): ReLU(inplace)
  (maxpool): MaxPool2d(kernel_size=3, stride=2, padding=1, dilation=1, ceil_mode=False)
  (layer1): Sequential(
    (0): BasicBlock(
      (conv1): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    )
    (1): BasicBlock(
      (conv1): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    )
  )
  (layer2): Sequential(
    (0): BasicBlock(
      (conv1): Conv2d(64, 128, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (downsample): Sequential(
        (0): Conv2d(64, 128, kernel_size=(1, 1), stride=(2, 2), bias=False)
        (1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      )
    )
    (1): BasicBlock(
      (conv1): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    )
  )
  (layer3): Sequential(
    (0): BasicBlock(
      (conv1): Conv2d(128, 256, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (downsample): Sequential(
        (0): Conv2d(128, 256, kernel_size=(1, 1), stride=(2, 2), bias=False)
        (1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      )
    )
    (1): BasicBlock(
      (conv1): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    )
  )
  (layer4): Sequential(
    (0): BasicBlock(
      (conv1): Conv2d(256, 512, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (downsample): Sequential(
        (0): Conv2d(256, 512, kernel_size=(1, 1), stride=(2, 2), bias=False)
        (1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      )
    )
    (1): BasicBlock(
      (conv1): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (relu): ReLU(inplace)
      (conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
      (bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    )
  )
  (avgpool): AvgPool2d(kernel_size=7, stride=1, padding=0)
  (fc): Sequential(
    (0): Dropout(p=0.3)
    (1): Linear(in_features=512, out_features=62, bias=True)
  )
)

　　

4.训练模型（支持自动GPU加速，GPU使用教程参考：[开发技巧]·PyTorch如何使用GPU加速）

def train(epochs):

    model = get_model(config.num_classes)
    print(model)
    loss_f = t.nn.CrossEntropyLoss()
    if(config.use_gpu):
        model = model.cuda()
        loss_f = loss_f.cuda()

    opt = t.optim.Adam(model.fc.parameters(),lr = config.lr)
    time_start = time.time()

    for epoch in range(epochs):
        train_loss = []
        train_acc = []
        test_loss = []
        test_acc = []
        model.train(True)
        print("Epoch {}/{}".format(epoch+1,epochs))
        for batch, datas in tqdm(enumerate(iter(dataloader["train"]))):
            x,y = datas
            if (config.use_gpu):
                x,y = x.cuda(),y.cuda()
            y_ = model(x)
            #print(x.shape,y.shape,y_.shape)
            _, pre_y_ = t.max(y_,1)
            pre_y = y
            #print(y_.shape)
            loss = loss_f(y_,pre_y)
            #print(y_.shape)
            acc = t.sum(pre_y_ == pre_y)

            loss.backward()
            opt.step()
            opt.zero_grad()
            if(config.use_gpu):
                loss = loss.cpu()
                acc = acc.cpu()
            train_loss.append(loss.data)
            train_acc.append(acc)
            #if((batch+1)%5 ==0):
        time_end = time.time()
        print("Batch {}, Train loss:{:.4f}, Train acc:{:.4f}, Time: {}"\
            .format(batch+1,np.mean(train_loss)/config.batch_size,np.mean(train_acc)/config.batch_size,(time_end-time_start)))
        time_start = time.time()

        model.train(False)
        for batch, datas in tqdm(enumerate(iter(dataloader["test"]))):
            x,y = datas
            if (config.use_gpu):
                x,y = x.cuda(),y.cuda()
            y_ = model(x)
            #print(x.shape,y.shape,y_.shape)
            _, pre_y_ = t.max(y_,1)
            pre_y = y
            #print(y_.shape)
            loss = loss_f(y_,pre_y)
            acc = t.sum(pre_y_ == pre_y)

            if(config.use_gpu):
                loss = loss.cpu()
                acc = acc.cpu()

            test_loss.append(loss.data)
            test_acc.append(acc)
        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))

        t.save(model,str(epoch+1)+"ttmodel.pkl")

if __name__ == "__main__":
    train(config.epochs)

　　

训练结果如下：

def train(epochs):

    model = get_model(config.num_classes)
    print(model)
    loss_f = t.nn.CrossEntropyLoss()
    if(config.use_gpu):
        model = model.cuda()
        loss_f = loss_f.cuda()

    opt = t.optim.Adam(model.fc.parameters(),lr = config.lr)
    time_start = time.time()

    for epoch in range(epochs):
        train_loss = []
        train_acc = []
        test_loss = []
        test_acc = []
        model.train(True)
        print("Epoch {}/{}".format(epoch+1,epochs))
        for batch, datas in tqdm(enumerate(iter(dataloader["train"]))):
            x,y = datas
            if (config.use_gpu):
                x,y = x.cuda(),y.cuda()
            y_ = model(x)
            #print(x.shape,y.shape,y_.shape)
            _, pre_y_ = t.max(y_,1)
            pre_y = y
            #print(y_.shape)
            loss = loss_f(y_,pre_y)
            #print(y_.shape)
            acc = t.sum(pre_y_ == pre_y)

            loss.backward()
            opt.step()
            opt.zero_grad()
            if(config.use_gpu):
                loss = loss.cpu()
                acc = acc.cpu()
            train_loss.append(loss.data)
            train_acc.append(acc)
            #if((batch+1)%5 ==0):
        time_end = time.time()
        print("Batch {}, Train loss:{:.4f}, Train acc:{:.4f}, Time: {}"\
            .format(batch+1,np.mean(train_loss)/config.batch_size,np.mean(train_acc)/config.batch_size,(time_end-time_start)))
        time_start = time.time()

        model.train(False)
        for batch, datas in tqdm(enumerate(iter(dataloader["test"]))):
            x,y = datas
            if (config.use_gpu):
                x,y = x.cuda(),y.cuda()
            y_ = model(x)
            #print(x.shape,y.shape,y_.shape)
            _, pre_y_ = t.max(y_,1)
            pre_y = y
            #print(y_.shape)
            loss = loss_f(y_,pre_y)
            acc = t.sum(pre_y_ == pre_y)

            if(config.use_gpu):
                loss = loss.cpu()
                acc = acc.cpu()

            test_loss.append(loss.data)
            test_acc.append(acc)
        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))

        t.save(model,str(epoch+1)+"ttmodel.pkl")

if __name__ == "__main__":
    train(config.epochs)

　　

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。