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CNN 网络适用于图片识别，卷积神经网络主要用于图片的处理识别。卷积神经网络，包括一下几部分，输入层、卷积层、池化层、全链接层和输出层。
使用 CIFAR-10 进行训练， CIFAR-10 中图片尺寸为 32 * 32。卷积层通过卷积核移动进行计算最终生成特征图。
通过池化层进行降维度
卷积网络结构从输入到输出， 3* 32*32 --> 10：
| 类型 | Weight | BIAS |
|---|---|---|
| 卷积(3, 12, 5) | (12, 3, 5, 5) | 12 |
| 卷积(12, 12, 5) | (12, 12, 5, 5) | 12 |
| Norm | 12 | 12 |
| 卷积(12, 24, 5) | (24, 12, 5, 5) | 24 |
| 卷积(24 24, 5) | (24, 24, 5, 5) | 24 |
| Norm | 24 | 24 |
| Linear | (10, 2400) | 10 |
训练分类模型
准备数据
from torchvision.datasets import CIFAR10
from torchvision.transforms import transforms
from torch.utils.data import DataLoader# Loading and normalizing the data.
# Define transformations for the training and test sets
transformations = transforms.Compose([transforms.ToTensor(),transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))
])# CIFAR10 dataset consists of 50K training images. We define the batch size of 10 to load 5,000 batches of images.
batch_size = 10
number_of_labels = 10 # Create an instance for training.
# When we run this code for the first time, the CIFAR10 train dataset will be downloaded locally.
train_set =CIFAR10(root="./data",train=True,transform=transformations,download=True)# Create a loader for the training set which will read the data within batch size and put into memory.
train_loader = DataLoader(train_set, batch_size=batch_size, shuffle=True, num_workers=0)
print("The number of images in a training set is: ", len(train_loader)*batch_size)# Create an instance for testing, note that train is set to False.
# When we run this code for the first time, the CIFAR10 test dataset will be downloaded locally.
test_set = CIFAR10(root="./data", train=False, transform=transformations, download=True)# Create a loader for the test set which will read the data within batch size and put into memory.
# Note that each shuffle is set to false for the test loader.
test_loader = DataLoader(test_set, batch_size=batch_size, shuffle=False, num_workers=0)
print("The number of images in a test set is: ", len(test_loader)*batch_size)print("The number of batches per epoch is: ", len(train_loader))
classes = ('plane', 'car', 'bird', 'cat', 'deer', 'dog', 'frog', 'horse', 'ship', 'truck')
创建网络
import torch
import torch.nn as nn
import torchvision
import torch.nn.functional as F# Define a convolution neural network
class Network(nn.Module):def __init__(self):super(Network, self).__init__()self.conv1 = nn.Conv2d(in_channels=3, out_channels=12, kernel_size=5, stride=1, padding=1)self.bn1 = nn.BatchNorm2d(12)self.conv2 = nn.Conv2d(in_channels=12, out_channels=12, kernel_size=5, stride=1, padding=1)self.bn2 = nn.BatchNorm2d(12)self.pool = nn.MaxPool2d(2,2)self.conv4 = nn.Conv2d(in_channels=12, out_channels=24, kernel_size=5, stride=1, padding=1)self.bn4 = nn.BatchNorm2d(24)self.conv5 = nn.Conv2d(in_channels=24, out_channels=24, kernel_size=5, stride=1, padding=1)self.bn5 = nn.BatchNorm2d(24)self.fc1 = nn.Linear(24*10*10, 10)def forward(self, input):output = F.relu(self.bn1(self.conv1(input))) output = F.relu(self.bn2(self.conv2(output))) output = self.pool(output) output = F.relu(self.bn4(self.conv4(output))) output = F.relu(self.bn5(self.conv5(output))) output = output.view(-1, 24*10*10)output = self.fc1(output)return output# Instantiate a neural network model
model = Network()
定义损失函数
使用交叉熵函数作为损失函数，交叉熵分为两种
- 二分类交叉熵函数
- 多分类交叉熵函数
loss_fn = nn.CrossEntropyLoss()
optimizer = Adam(model.parameters(), lr=0.001, weight_decay=0.0001)
模型训练
from torch.autograd import Variable# Function to save the model
def saveModel():path = "./myFirstModel.pth"torch.save(model.state_dict(), path)# Function to test the model with the test dataset and print the accuracy for the test images
def testAccuracy():model.eval()accuracy = 0.0total = 0.0device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")with torch.no_grad():for data in test_loader:images, labels = data# run the model on the test set to predict labelsoutputs = model(images.to(device))# the label with the highest energy will be our prediction_, predicted = torch.max(outputs.data, 1)total += labels.size(0)accuracy += (predicted == labels.to(device)).sum().item()# compute the accuracy over all test imagesaccuracy = (100 * accuracy / total)return(accuracy)# Training function. We simply have to loop over our data iterator and feed the inputs to the network and optimize.
def train(num_epochs):best_accuracy = 0.0# Define your execution devicedevice = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")print("The model will be running on", device, "device")# Convert model parameters and buffers to CPU or Cudamodel.to(device)for epoch in range(num_epochs): # loop over the dataset multiple timesrunning_loss = 0.0running_acc = 0.0for i, (images, labels) in enumerate(train_loader, 0):# get the inputsimages = Variable(images.to(device))labels = Variable(labels.to(device))# zero the parameter gradientsoptimizer.zero_grad()# predict classes using images from the training setoutputs = model(images)# compute the loss based on model output and real labelsloss = loss_fn(outputs, labels)# backpropagate the lossloss.backward()# adjust parameters based on the calculated gradientsoptimizer.step()# Let's print statistics for every 1,000 imagesrunning_loss += loss.item() # extract the loss valueif i % 1000 == 999: # print every 1000 (twice per epoch) print('[%d, %5d] loss: %.3f' %(epoch + 1, i + 1, running_loss / 1000))# zero the lossrunning_loss = 0.0# Compute and print the average accuracy fo this epoch when tested over all 10000 test imagesaccuracy = testAccuracy()print('For epoch', epoch+1,'the test accuracy over the whole test set is %d %%' % (accuracy))# we want to save the model if the accuracy is the bestif accuracy > best_accuracy:saveModel()best_accuracy = accuracy
测试模型
import matplotlib.pyplot as plt
import numpy as np# Function to show the images
def imageshow(img):img = img / 2 + 0.5 # unnormalizenpimg = img.numpy()plt.imshow(np.transpose(npimg, (1, 2, 0)))plt.show()# Function to test the model with a batch of images and show the labels predictions
def testBatch():# get batch of images from the test DataLoader images, labels = next(iter(test_loader))# show all images as one image gridimageshow(torchvision.utils.make_grid(images))# Show the real labels on the screen print('Real labels: ', ' '.join('%5s' % classes[labels[j]] for j in range(batch_size)))# Let's see what if the model identifiers the labels of those exampleoutputs = model(images)# We got the probability for every 10 labels. The highest (max) probability should be correct label_, predicted = torch.max(outputs, 1)# Let's show the predicted labels on the screen to compare with the real onesprint('Predicted: ', ' '.join('%5s' % classes[predicted[j]] for j in range(batch_size)))
执行模型
if __name__ == "__main__":# Let's build our modeltrain(5)print('Finished Training')# Test which classes performed welltestAccuracy()# Let's load the model we just created and test the accuracy per labelmodel = Network()path = "myFirstModel.pth"model.load_state_dict(torch.load(path))# Test with batch of imagestestBatch()
总结
pytorch 搭建一个 CNN 模型比较简单，5 轮训练之后，效果就可以达到 60%，10 张图片中预测对了 6 张。