這篇文章主要介紹了Pytorch寫數(shù)字識別LeNet模型，LeNet-5是一個較簡單的卷積神經(jīng)網(wǎng)絡，??LeNet-5?這個網(wǎng)絡雖然很小，但是它包含了深度學習的基本模塊：卷積層，池化層，全連接層。是其他深度學習模型的基礎，?這里我們對LeNet-5進行深入分析,需要的朋友可以參考下

LeNet網(wǎng)絡

LeNet網(wǎng)絡過卷積層時候保持分辨率不變，過池化層時候分辨率變小。實現(xiàn)如下

from PIL import Image
import cv2
import matplotlib.pyplot as plt
import torchvision
from torchvision import transforms
import torch
from torch.utils.data import DataLoader
import torch.nn as nn
import numpy as np
import tqdm as tqdm

class LeNet(nn.Module):
? ? def __init__(self) -> None:
? ? ? ? super().__init__()
? ? ? ? self.sequential = nn.Sequential(nn.Conv2d(1,6,kernel_size=5,padding=2),nn.Sigmoid(),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.AvgPool2d(kernel_size=2,stride=2),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.Conv2d(6,16,kernel_size=5),nn.Sigmoid(),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.AvgPool2d(kernel_size=2,stride=2),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.Flatten(),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.Linear(16*25,120),nn.Sigmoid(),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.Linear(120,84),nn.Sigmoid(),
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? nn.Linear(84,10))
? ? ? ??
? ??
? ? def forward(self,x):
? ? ? ? return self.sequential(x)

class MLP(nn.Module):
? ? def __init__(self) -> None:
? ? ? ? super().__init__()
? ? ? ? self.sequential = nn.Sequential(nn.Flatten(),
? ? ? ? ? ? ? ? ? ? ? ? ? nn.Linear(28*28,120),nn.Sigmoid(),
? ? ? ? ? ? ? ? ? ? ? ? ? nn.Linear(120,84),nn.Sigmoid(),
? ? ? ? ? ? ? ? ? ? ? ? ? nn.Linear(84,10))
? ? ? ??
? ??
? ? def forward(self,x):
? ? ? ? return self.sequential(x)

epochs = 15
batch = 32
lr=0.9
loss = nn.CrossEntropyLoss()
model = LeNet()
optimizer = torch.optim.SGD(model.parameters(),lr)
device = torch.device('cuda')
root = r"./"
trans_compose ?= transforms.Compose([transforms.ToTensor(),
? ? ? ? ? ? ? ? ? ? ])
train_data = torchvision.datasets.MNIST(root,train=True,transform=trans_compose,download=True)
test_data = torchvision.datasets.MNIST(root,train=False,transform=trans_compose,download=True)
train_loader = DataLoader(train_data,batch_size=batch,shuffle=True)
test_loader = DataLoader(test_data,batch_size=batch,shuffle=False)

model.to(device)
loss.to(device)
# model.apply(init_weights)
for epoch in range(epochs):
? train_loss = 0
? test_loss = 0
? correct_train = 0
? correct_test = 0
? for index,(x,y) in enumerate(train_loader):
? ? x = x.to(device)
? ? y = y.to(device)
? ? predict = model(x)
? ? L = loss(predict,y)
? ? optimizer.zero_grad()
? ? L.backward()
? ? optimizer.step()
? ? train_loss = train_loss + L
? ? correct_train += (predict.argmax(dim=1)==y).sum()
? acc_train = correct_train/(batch*len(train_loader))
? with torch.no_grad():
? ? for index,(x,y) in enumerate(test_loader):
? ? ? [x,y] = [x.to(device),y.to(device)]
? ? ? predict = model(x)
? ? ? L1 = loss(predict,y)
? ? ? test_loss = test_loss + L1
? ? ? correct_test += (predict.argmax(dim=1)==y).sum()
? ? acc_test = correct_test/(batch*len(test_loader))
? print(f'epoch:{epoch},train_loss:{train_loss/batch},test_loss:{test_loss/batch},acc_train:{acc_train},acc_test:{acc_test}')

訓練結果

epoch:12,train_loss:2.235553741455078,test_loss:0.3947642743587494,acc_train:0.9879833459854126,acc_test:0.9851238131523132
epoch:13,train_loss:2.028963804244995,test_loss:0.3220392167568207,acc_train:0.9891499876976013,acc_test:0.9875199794769287
epoch:14,train_loss:1.8020273447036743,test_loss:0.34837451577186584,acc_train:0.9901833534240723,acc_test:0.98702073097229

泛化能力測試

找了一張圖片，將其分割成只含一個數(shù)字的圖片進行測試

images_np = cv2.imread("/content/R-C.png",cv2.IMREAD_GRAYSCALE)
h,w = images_np.shape
images_np = np.array(255*torch.ones(h,w))-images_np#圖片反色
images = Image.fromarray(images_np)
plt.figure(1)
plt.imshow(images)
test_images = []
for i in range(10):
? for j in range(16):
? ? test_images.append(images_np[h//10*i:h//10+h//10*i,w//16*j:w//16*j+w//16])
sample = test_images[77]
sample_tensor = torch.tensor(sample).unsqueeze(0).unsqueeze(0).type(torch.FloatTensor).to(device)
sample_tensor = torch.nn.functional.interpolate(sample_tensor,(28,28))
predict = model(sample_tensor)
output = predict.argmax()
print(output)
plt.figure(2)
plt.imshow(np.array(sample_tensor.squeeze().to('cpu')))

此時預測結果為4，預測正確。從這段代碼中可以看到有一個反色的步驟，若不反色，結果會受到影響，如下圖所示，預測為0，錯誤。
模型用于輸入的圖片是單通道的黑白圖片，這里由于可視化出現(xiàn)了黃色，但實際上是黑白色，反色操作說明了數(shù)據(jù)的預處理十分的重要，很多數(shù)據(jù)如果是不清理過是無法直接用于推理的。

將所有用來泛化性測試的圖片進行準確率測試：

correct = 0
i = 0
cnt = 1
for sample in test_images:
? sample_tensor = torch.tensor(sample).unsqueeze(0).unsqueeze(0).type(torch.FloatTensor).to(device)
? sample_tensor = torch.nn.functional.interpolate(sample_tensor,(28,28))
? predict = model(sample_tensor)
? output = predict.argmax()
? if(output==i):
? ? correct+=1
? if(cnt%16==0):
? ? i+=1
? cnt+=1
acc_g = correct/len(test_images)
print(f'acc_g:{acc_g}')

如果不反色，acc_g=0.15