深度学习入门基础教程(三) CNN做MNIST数据集图像分类 pytorch版代码

短命女 2022-01-22 15:39 372阅读 0赞

### 一.  原理解读 ###

这个和上一篇教程一样，都是简单的图像分类，只是针对的数据集不同。鉴于是入门教程，再仔细写一遍

分享一篇我觉得非常适合新手理解CNN的博文 [https://blog.csdn.net/XYlittlework/article/details/79903225][https_blog.csdn.net_XYlittlework_article_details_79903225]

MNIST数据集(训练集6万张，测试集1万张，每张灰度图28\*28\*1(单通道)，数字0-9对应标签值0-9)如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5OTM4NjY2_size_16_color_FFFFFF_t_70][]

### 二.  pytorch版完整代码复现 ###

**1. 全代码名称展示**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5OTM4NjY2_size_16_color_FFFFFF_t_70 1][]

因为是最简单的一个手写体数据集，随便跑个几十轮，在测试集上的准确率就到了99%以上

**2. 代码**

import torch
    import torch.nn as nn
    from torchvision.datasets import MNIST
    from torchvision import transforms
    from torch.utils.data import DataLoader,Dataset
    from torch.optim import Adam
    import os
    import shutil
    
    """
    torch.nn是专门为神经网络设计的模块化接口。nn构建于autograd之上，可以用来定义和运行神经网络。
    nn.Module是nn中十分重要的类,包含网络各层的定义及forward方法。
    
    定义自已的网络：
        需要继承nn.Module类，并实现forward方法。
        一般把网络中具有可学习参数的层放在构造函数__init__()中，
        不具有可学习参数的层(如ReLU)可放在构造函数中，也可不放在构造函数中(而在forward中使用nn.functional来代替)。    
        只要在nn.Module的子类中定义了forward函数，backward函数就会被自动实现(利用Autograd)。
    
    注：Pytorch基于nn.Module构建的模型中，只支持mini-batch的Variable输入方式，
        比如，只有一张输入图片，也需要变成 N x C x H x W 的形式：    
        input_image = torch.FloatTensor(1, 28, 28)   
        input_image = input_image.unsqueeze(0)   # 1 x 1 x 28 x 28
    """
    class Unit(nn.Module):#以上解释了这里为什么必须写出继承类nn.Module
        def __init__(self,inc,ouc):
            super(Unit,self).__init__()
            self.unit_net = nn.Sequential(nn.Conv2d(inc,ouc,kernel_size=3,padding=1),
                          nn.BatchNorm2d(ouc),
                          nn.ReLU())
        def forward(self, x):
            return self.unit_net(x)
    
    class Net(nn.Module):
        def __init__(self):
            super(Net,self).__init__()
            self.net = nn.Sequential(Unit(1,32),#32*32
                                     Unit(32,32),
                                     Unit(32,32),
    
                                     nn.MaxPool2d(2),#16
    
                                     Unit(32,64),
                                     Unit(64,64),
                                     Unit(64,64),
                                     Unit(64,64),
    
                                     nn.MaxPool2d(2),#8
    
                                     Unit(64, 128),
                                     Unit(128, 128),
                                     Unit(128, 128),
                                     Unit(128, 128),
    
                                     nn.MaxPool2d(2),#4
    
                                     Unit(128,128),
                                     Unit(128,128),
                                     Unit(128,128),
    
                                     nn.AvgPool2d(4)#1
                                     )
            self.fc = nn.Linear(128, 10)
    
        def forward(self, x):
            y = self.net(x)
            y = y.view(-1,128)
            return self.fc(y)
    
    '训练集转换'
    train_transforms = transforms.Compose([
        transforms.RandomHorizontalFlip(),#随机翻转
        transforms.ToTensor(),
        transforms.Normalize((0.5,0.5,0.5), (0.5,0.5,0.5))])
    'train=True加载训练集'
    train_set = MNIST('./data/',train=True,transform=train_transforms,download=True)
    train_dataloader = DataLoader(train_set,batch_size=512,shuffle=True)
    
    '测试集转换'
    test_transforms = transforms.Compose([
        transforms.ToTensor(),
        transforms.Normalize((0.5,0.5,0.5), (0.5,0.5,0.5))])
    'train=False加载测试集'
    test_set = MNIST('./data/',train=False,transform=test_transforms,download=True)
    test_dataloader = DataLoader(test_set,batch_size=512,shuffle=False)
    
    param_path = r'./param/mnist_cnn.pkl'
    tmp_param_path = r'./param/mnist_cnn_temp.pkl'
    
    CUDA = torch.cuda.is_available()
    # print(CUDA)
    module = Net()
    if CUDA:
        module.cuda()
    optimizer = Adam(module.parameters(),lr=0.001,weight_decay=0.0001)
    loss_f = nn.CrossEntropyLoss()#分类用交叉熵
    
    '创建一个学习率调整函数，每30个周期将学习率除以10'
    def adjust_lr_rate(epoch):
        lr = 0.001
        if epoch>180:
            lr = lr / 1000000
        elif epoch>150:
            lr = lr / 100000
        elif epoch>120:
            lr = lr / 10000
        elif epoch>90:
            lr = lr / 1000
        elif epoch>60:
            lr = lr / 100
        elif epoch>30:
            lr = lr / 10
        for param_group in optimizer.param_groups:
            param_group['lr'] = lr
    
    def test():#测试集1万张
        test_acc = 0
        module.eval()
        for j,(imgs, labels) in enumerate(test_dataloader):#每次处理512张
            if CUDA:
                imgs = imgs.cuda()
                labels = labels.cuda()
            outs = module(imgs)
            #训练求loss是为了做权重更新，测试里不需要
            _, prediction = torch.max(outs, 1)
            test_acc += torch.sum(prediction == labels)
        test_acc = test_acc.cpu().item() / 10000
        return test_acc
    
    def train(num_epoch):#训练集6万张
        if os.path.exists(param_path):
            module.load_state_dict(torch.load(param_path))
        for epoch in range(num_epoch):
            train_loss = 0
            train_acc = 0
            module.train()
            for i, (imgs, labels) in enumerate(train_dataloader):#每次处理512张
                # print('labels:',labels)#每个标签对应一个0-9的数字
                if CUDA:
                    imgs = imgs.cuda()
                    labels = labels.cuda()
                outs = module(imgs)
                # print(outs.shape)
                # print('outs:',outs)
                loss = loss_f(outs, labels)
    
                optimizer.zero_grad()
                loss.backward()
                optimizer.step()
    
                # print('1111',loss)
                # print('2222',loss.data)#tensor且GPU
                # print('3333',loss.cpu())
                # print('4444',loss.cpu().data)#tensor且CPU
                # # print('5555',loss.cpu().data[0])#报错 IndexError: invalid index of a 0-dim tensor. Use tensor.item() to convert a 0-dim tensor to a Python number
                # # print('6666',loss.cpu().numpy())#报错 RuntimeError: Can't call numpy() on Variable that requires grad. Use var.detach().numpy() instead.
                # print('7777',loss.cpu().detach().numpy())
                # print('8888',loss.cpu().data.numpy())
                # print('9999',loss.cpu().item())
                # print('aaaa',loss.item())#后四者一样，都是把数值取出来
                train_loss += loss.cpu().item() * imgs.size(0)#imgs.size(0)批次
                '分类问题，常用torch.max(outs,1)得到索引来表示类别'
                _, prediction = torch.max(outs,1)#prediction对应每行最大值所在位置的索引值，即0-9
                train_acc += torch.sum(prediction == labels)
                # print(train_acc.cpu().item())
    
            adjust_lr_rate(epoch)
            train_loss = train_loss / 60000
            train_acc = train_acc.cpu().item() / 60000 #此处求概率必须用item()把数值取出，否则求出的不是小数
    
            '每训练完一个epoch，用测试集做一遍评估'
            test_acc = test()
            best_acc = 0
            if test_acc > best_acc:
                best_acc = test_acc
                if os.path.exists(tmp_param_path):
                    shutil.copyfile(tmp_param_path, param_path)#防权重损坏
                torch.save(module.state_dict(),tmp_param_path)
            print('Epoch:',epoch,'Train_Loss:',train_loss,'Train_Acc:',train_acc,'Test_Acc:',test_acc)
    
    train(1000)

**3. 扩展 **

用如上训练好的模型做推断

import torch
    import torch.nn as nn
    from torchvision import transforms
    from torchvision.models import squeezenet1_1
    from PIL import Image
    
    class Unit(nn.Module):#以上解释了这里为什么必须写出继承类nn.Module
        def __init__(self,inc,ouc):
            super(Unit,self).__init__()
            self.unit_net = nn.Sequential(nn.Conv2d(inc,ouc,kernel_size=3,padding=1),
                          nn.BatchNorm2d(ouc),
                          nn.ReLU())
        def forward(self, x):
            return self.unit_net(x)
    
    class Net(nn.Module):
        def __init__(self):
            super(Net,self).__init__()
            self.net = nn.Sequential(Unit(1,32),#32*32
                                     Unit(32,32),
                                     Unit(32,32),
    
                                     nn.MaxPool2d(2),#16
    
                                     Unit(32,64),
                                     Unit(64,64),
                                     Unit(64,64),
                                     Unit(64,64),
    
                                     nn.MaxPool2d(2),#8
    
                                     Unit(64, 128),
                                     Unit(128, 128),
                                     Unit(128, 128),
                                     Unit(128, 128),
    
                                     nn.MaxPool2d(2),#4
    
                                     Unit(128,128),
                                     Unit(128,128),
                                     Unit(128,128),
    
                                     nn.AvgPool2d(4)#1
                                     )
            self.fc = nn.Linear(128, 10)
    
        def forward(self, x):
            y = self.net(x)
            y = y.view(-1,128)
            return self.fc(y)
    
    CUDA = torch.cuda.is_available()
    # module = squeezenet1_1(pretrained=True)#torchvision官方内置模型直接调用
    module = Net()#自己的模型调用
    module.load_state_dict(torch.load(r'./param/mnist_cnn.pkl'))
    module.eval()
    if CUDA:
        module.cuda()
    
    def predict_img(img_path):
        img = Image.open(img_path)
        img2data = transforms.Compose([
                            transforms.Resize(28),#因为这个模型是专门针对32*32的CIFAR10
                            transforms.ToTensor(),
                            transforms.Normalize((0.5,0.5,0.5),(0.5,0.5,0.5))])
        data = img2data(img)
        '因为PyTorch将所有的图像当做批次,默认只处理四维数据'
        data = data.unsqueeze_(0)
        if CUDA:
            data = data.cuda()
        out = module(data)
        # print(out)
        _,index = torch.max(out,1)
        return index.item()
    
    if __name__ == '__main__':
        index = predict_img(r'C:\Users\87419\Desktop/00.jpg')
        print(index)

随便拿一张灰度图测试一下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5OTM4NjY2_size_16_color_FFFFFF_t_70 2][]

注：测试图也需是灰度图

RGB图转灰度图代码

from PIL import Image
    
    I = Image.open(r'C:\Users\87419\Desktop/0.jpg').convert('L')
    I.save(r'C:\Users\87419\Desktop/00.jpg')#灰度图

[https_blog.csdn.net_XYlittlework_article_details_79903225]: https://blog.csdn.net/XYlittlework/article/details/79903225
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5OTM4NjY2_size_16_color_FFFFFF_t_70]: /images/20220122/42e0a3b4c25e49fbb7223455c422dfbc.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5OTM4NjY2_size_16_color_FFFFFF_t_70 1]: /images/20220122/a60d14b1c8024f33899745bec5d4eb8a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5OTM4NjY2_size_16_color_FFFFFF_t_70 2]: /images/20220122/9d8e3dbf5cef44228646c062e5e6dde6.png