论文原文：《Learning a Similarity Metric Discriminatively, with Application to Face
Verification》
http://yann.lecun.com/exdb/publis/pdf/chopra-05.pdf
1. 数据集
数据采用的是AT&T人脸数据。共40个人，每个人有10张脸。数据集下载：AT&T
2. Imports
All the imports are defined here
import torchvision
import torchvision.datasets as dset
import torchvision.transforms as transforms
from torch.utils.data import DataLoader,Dataset
import matplotlib.pyplot as plt
import torchvision.utils
import numpy as np
import random
from PIL import Image
import torch
from torch.autograd import Variable
import PIL.ImageOps
import torch.nn as nn
from torch import optim
import torch.nn.functional as F3. Helper functions
Set of helper functions
def imshow(img,text=None,should_save=False):
npimg = img.numpy()
plt.axis("off")
if text:
plt.text(75, 8, text, style='italic',fontweight='bold',
bbox={'facecolor':'white', 'alpha':0.8, 'pad':10})
plt.imshow(np.transpose(npimg, (1, 2, 0)))
plt.show()
def show_plot(iteration,loss):
plt.plot(iteration,loss)
plt.show()4. Configuration Class
A simple class to manage configuration
class Config():
training_dir = "./data/faces/training/"
testing_dir = "./data/faces/testing/"
train_batch_size = 64
train_number_epochs = 1005. Custom Dataset Class
This dataset generates a pair of images. 0 for geniune pair and 1 for imposter pair
class SiameseNetworkDataset(Dataset):
def __init__(self,imageFolderDataset,transform=None,should_invert=True):
self.imageFolderDataset = imageFolderDataset
self.transform = transform
self.should_invert = should_invert
def __getitem__(self,index):
img0_tuple = random.choice(self.imageFolderDataset.imgs)
#we need to make sure approx 50% of images are in the same class
should_get_same_class = random.randint(0,1)
if should_get_same_class:
while True:
#keep looping till the same class image is found
img1_tuple = random.choice(self.imageFolderDataset.imgs)
if img0_tuple[1]==img1_tuple[1]:
break
else:
while True:
#keep looping till a different class image is found
img1_tuple = random.choice(self.imageFolderDataset.imgs)
if img0_tuple[1] !=img1_tuple[1]:
break
img0 = Image.open(img0_tuple[0])
img1 = Image.open(img1_tuple[0])
img0 = img0.convert("L")
img1 = img1.convert("L")
if self.should_invert:
img0 = PIL.ImageOps.invert(img0)
img1 = PIL.ImageOps.invert(img1)
if self.transform is not None:
img0 = self.transform(img0)
img1 = self.transform(img1)
return img0, img1 , torch.from_numpy(np.array([int(img1_tuple[1]!=img0_tuple[1])],dtype=np.float32))
def __len__(self):
return len(self.imageFolderDataset.imgs)6. Using Image Folder Dataset
folder_dataset = dset.ImageFolder(root=Config.training_dir)
siamese_dataset = SiameseNetworkDataset(imageFolderDataset=folder_dataset,
transform=transforms.Compose([transforms.Resize((100,100)),
transforms.ToTensor()
])
,should_invert=False)7. Visualising some of the data
The top row and the bottom row of any column is one pair. The 0s and 1s correspond to the column of the image. 1 indiciates dissimilar, and 0 indicates similar.
vis_dataloader = DataLoader(siamese_dataset,
shuffle=True,
num_workers=8,
batch_size=8)
dataiter = iter(vis_dataloader)
example_batch = next(dataiter)
concatenated = torch.cat((example_batch[0],example_batch[1]),0)
imshow(torchvision.utils.make_grid(concatenated))
print(example_batch[2].numpy())
[[1.]
[1.]
[0.]
[0.]
[1.]
[1.]
[1.]
[1.]]
8. Neural Net Definition
We will use a standard convolutional neural network
class SiameseNetwork(nn.Module):
def __init__(self):
super(SiameseNetwork, self).__init__()
self.cnn1 = nn.Sequential(
nn.ReflectionPad2d(1),
nn.Conv2d(1, 4, kernel_size=3),
nn.ReLU(inplace=True),
nn.BatchNorm2d(4),
nn.ReflectionPad2d(1),
nn.Conv2d(4, 8, kernel_size=3),
nn.ReLU(inplace=True),
nn.BatchNorm2d(8),
nn.ReflectionPad2d(1),
nn.Conv2d(8, 8, kernel_size=3),
nn.ReLU(inplace=True),
nn.BatchNorm2d(8),
)
self.fc1 = nn.Sequential(
nn.Linear(8*100*100, 500),
nn.ReLU(inplace=True),
nn.Linear(500, 500),
nn.ReLU(inplace=True),
nn.Linear(500, 5))
def forward_once(self, x):
output = self.cnn1(x)
output = output.view(output.size()[0], -1)
output = self.fc1(output)
return output
def forward(self, input1, input2):
output1 = self.forward_once(input1)
output2 = self.forward_once(input2)
return output1, output29. Contrastive Loss
class ContrastiveLoss(torch.nn.Module):
"""
Contrastive loss function.
Based on: http://yann.lecun.com/exdb/publis/pdf/hadsell-chopra-lecun-06.pdf
"""
def __init__(self, margin=2.0):
super(ContrastiveLoss, self).__init__()
self.margin = margin
def forward(self, output1, output2, label):
euclidean_distance = F.pairwise_distance(output1, output2, keepdim = True)
loss_contrastive = torch.mean((1-label) * torch.pow(euclidean_distance, 2) +
(label) * torch.pow(torch.clamp(self.margin - euclidean_distance, min=0.0), 2))
return loss_contrastive10. Training Time!
train_dataloader = DataLoader(siamese_dataset,
shuffle=True,
num_workers=8,
batch_size=Config.train_batch_size)
net = SiameseNetwork().cuda()
criterion = ContrastiveLoss()
optimizer = optim.Adam(net.parameters(),lr = 0.0005 )
counter = []
loss_history = []
iteration_number= 0
for epoch in range(0,Config.train_number_epochs):
for i, data in enumerate(train_dataloader,0):
img0, img1 , label = data
img0, img1 , label = img0.cuda(), img1.cuda() , label.cuda()
optimizer.zero_grad()
output1,output2 = net(img0,img1)
loss_contrastive = criterion(output1,output2,label)
loss_contrastive.backward()
optimizer.step()
if i %10 == 0 :
print("Epoch number {}\n Current loss {}\n".format(epoch,loss_contrastive.item()))
iteration_number +=10
counter.append(iteration_number)
loss_history.append(loss_contrastive.item())
show_plot(counter,loss_history)
参考
https://blog.csdn.net/yukai08008/article/details/108236724
https://www.cnblogs.com/king-lps/p/8342452.html
https://github.com/harveyslash/Facial-Similarity-with-Siamese-Networks-in-Pytorch/
