pytorch finetuning 自己的圖片進行訓練操作
一、pytorch finetuning 自己的圖片進行訓練
這種讀取圖片的方式用的是torch自帶的 ImageFolder,讀取的文件夾必須在一個大的子文件下,按類別歸好類。
就像我現在要區分三個類別。
#perpare data set #train data train_data=torchvision.datasets.ImageFolder('F:/eyeDataSet/trainData',transform=transforms.Compose( [ transforms.Scale(256), transforms.CenterCrop(224), transforms.ToTensor() ])) print(len(train_data)) train_loader=DataLoader(train_data,batch_size=20,shuffle=True)
然後就是fine tuning自己的網絡,在torch中可以對整個網絡修改後,訓練全部的參數也可以隻訓練其中的一部分,我這裡就隻訓練最後一個全連接層。
torchvision中提供瞭很多常用的模型,比如resnet ,Vgg,Alexnet等等
# prepare model mode1_ft_res18=torchvision.models.resnet18(pretrained=True) for param in mode1_ft_res18.parameters(): param.requires_grad=False num_fc=mode1_ft_res18.fc.in_features mode1_ft_res18.fc=torch.nn.Linear(num_fc,3)
定義自己的優化器,註意這裡的參數隻傳入最後一層的
#loss function and optimizer criterion=torch.nn.CrossEntropyLoss() #parameters only train the last fc layer optimizer=torch.optim.Adam(mode1_ft_res18.fc.parameters(),lr=0.001)
然後就可以開始訓練瞭,定義好各種參數。
#start train #label not one-hot encoder EPOCH=1 for epoch in range(EPOCH): train_loss=0. train_acc=0. for step,data in enumerate(train_loader): batch_x,batch_y=data batch_x,batch_y=Variable(batch_x),Variable(batch_y) #batch_y not one hot #out is the probability of eatch class # such as one sample[-1.1009 0.1411 0.0320],need to calculate the max index # out shape is batch_size * class out=mode1_ft_res18(batch_x) loss=criterion(out,batch_y) train_loss+=loss.data[0] # pred is the expect class #batch_y is the true label pred=torch.max(out,1)[1] train_correct=(pred==batch_y).sum() train_acc+=train_correct.data[0] optimizer.zero_grad() loss.backward() optimizer.step() if step%14==0: print('Epoch: ',epoch,'Step',step, 'Train_loss: ',train_loss/((step+1)*20),'Train acc: ',train_acc/((step+1)*20))
測試部分和訓練部分類似這裡就不一一說明。
這樣就完整瞭對自己網絡的訓練測試,完整代碼如下:
import torch import numpy as np import torchvision from torchvision import transforms,utils from torch.utils.data import DataLoader from torch.autograd import Variable #perpare data set #train data train_data=torchvision.datasets.ImageFolder('F:/eyeDataSet/trainData',transform=transforms.Compose( [ transforms.Scale(256), transforms.CenterCrop(224), transforms.ToTensor() ])) print(len(train_data)) train_loader=DataLoader(train_data,batch_size=20,shuffle=True) #test data test_data=torchvision.datasets.ImageFolder('F:/eyeDataSet/testData',transform=transforms.Compose( [ transforms.Scale(256), transforms.CenterCrop(224), transforms.ToTensor() ])) test_loader=DataLoader(test_data,batch_size=20,shuffle=True) # prepare model mode1_ft_res18=torchvision.models.resnet18(pretrained=True) for param in mode1_ft_res18.parameters(): param.requires_grad=False num_fc=mode1_ft_res18.fc.in_features mode1_ft_res18.fc=torch.nn.Linear(num_fc,3) #loss function and optimizer criterion=torch.nn.CrossEntropyLoss() #parameters only train the last fc layer optimizer=torch.optim.Adam(mode1_ft_res18.fc.parameters(),lr=0.001) #start train #label not one-hot encoder EPOCH=1 for epoch in range(EPOCH): train_loss=0. train_acc=0. for step,data in enumerate(train_loader): batch_x,batch_y=data batch_x,batch_y=Variable(batch_x),Variable(batch_y) #batch_y not one hot #out is the probability of eatch class # such as one sample[-1.1009 0.1411 0.0320],need to calculate the max index # out shape is batch_size * class out=mode1_ft_res18(batch_x) loss=criterion(out,batch_y) train_loss+=loss.data[0] # pred is the expect class #batch_y is the true label pred=torch.max(out,1)[1] train_correct=(pred==batch_y).sum() train_acc+=train_correct.data[0] optimizer.zero_grad() loss.backward() optimizer.step() if step%14==0: print('Epoch: ',epoch,'Step',step, 'Train_loss: ',train_loss/((step+1)*20),'Train acc: ',train_acc/((step+1)*20)) #print('Epoch: ', epoch, 'Train_loss: ', train_loss / len(train_data), 'Train acc: ', train_acc / len(train_data)) # test model mode1_ft_res18.eval() eval_loss=0 eval_acc=0 for step ,data in enumerate(test_loader): batch_x,batch_y=data batch_x,batch_y=Variable(batch_x),Variable(batch_y) out=mode1_ft_res18(batch_x) loss = criterion(out, batch_y) eval_loss += loss.data[0] # pred is the expect class # batch_y is the true label pred = torch.max(out, 1)[1] test_correct = (pred == batch_y).sum() eval_acc += test_correct.data[0] optimizer.zero_grad() loss.backward() optimizer.step() print( 'Test_loss: ', eval_loss / len(test_data), 'Test acc: ', eval_acc / len(test_data))
二、PyTorch 利用預訓練模型進行Fine-tuning
在Deep Learning領域,很多子領域的應用,比如一些動物識別,食物的識別等,公開的可用的數據庫相對於ImageNet等數據庫而言,其規模太小瞭,無法利用深度網絡模型直接train from scratch,容易引起過擬合,這時就需要把一些在大規模數據庫上已經訓練完成的模型拿過來,在目標數據庫上直接進行Fine-tuning(微調),這個已經經過訓練的模型對於目標數據集而言,隻是一種相對較好的參數初始化方法而已,尤其是大數據集與目標數據集結構比較相似的話,經過在目標數據集上微調能夠得到不錯的效果。
Fine-tune預訓練網絡的步驟:
1. 首先更改預訓練模型分類層全連接層的數目,因為一般目標數據集的類別數與大規模數據庫的類別數不一致,更改為目標數據集上訓練集的類別數目即可,一致的話則無需更改;
2. 把分類器前的網絡的所有層的參數固定,即不讓它們參與學習,不進行反向傳播,隻訓練分類層的網絡,這時學習率可以設置的大一點,如是原來初始學習率的10倍或幾倍或0.01等,這時候網絡訓練的比較快,因為除瞭分類層,其它層不需要進行反向傳播,可以多嘗試不同的學習率設置。
3.接下來是設置相對較小的學習率,對整個網絡進行訓練,這時網絡訓練變慢啦。
下面對利用PyTorch深度學習框架Fine-tune預訓練網絡的過程中涉及到的固定可學習參數,對不同的層設置不同的學習率等進行詳細講解。
1. PyTorch對某些層固定網絡的可學習參數的方法:
class Net(nn.Module): def __init__(self, num_classes=546): super(Net, self).__init__() self.features = nn.Sequential( nn.Conv2d(1, 64, kernel_size=3, stride=2, padding=1), nn.BatchNorm2d(64), nn.ReLU(inplace=True), nn.Conv2d(64, 64, kernel_size=3, stride=1, padding=1), nn.BatchNorm2d(64), nn.ReLU(inplace=True), ) self.Conv1_1 = nn.Sequential( nn.Conv2d(64, 64, kernel_size=3, stride=1, padding=1), nn.BatchNorm2d(64), nn.ReLU(inplace=True), nn.Conv2d(64, 64, kernel_size=3, stride=1, padding=1), nn.BatchNorm2d(64), ) for p in self.parameters(): p.requires_grad=False self.Conv1_2 = nn.Sequential( nn.Conv2d(64, 64, kernel_size=3, stride=1, padding=1), nn.BatchNorm2d(64), nn.ReLU(inplace=True), nn.Conv2d(64, 64, kernel_size=3, stride=1, padding=1), nn.BatchNorm2d(64), )
如上述代碼,則模型Net網絡中self.features與self.Conv1_1層中的參數便是固定,不可學習的。這主要看代碼:
for p in self.parameters(): p.requires_grad=False
插入的位置,這段代碼前的所有層的參數是不可學習的,也就沒有反向傳播過程。也可以指定某一層的參數不可學習,如下:
for p in self.features.parameters(): p.requires_grad=False
則 self.features層所有參數均是不可學習的。
註意,上述代碼設置若要真正生效,在訓練網絡時需要在設置優化器如下:
optimizer = torch.optim.SGD(filter(lambda p: p.requires_grad, model.parameters()), args.lr, momentum=args.momentum, weight_decay=args.weight_decay)
2. PyTorch之為不同的層設置不同的學習率
model = Net() conv1_2_params = list(map(id, model.Conv1_2.parameters())) base_params = filter(lambda p: id(p) not in conv1_2_params, model.parameters()) optimizer = torch.optim.SGD([ {'params': base_params}, {'params': model.Conv1_2.parameters(), 'lr': 10 * args.lr}], args.lr, momentum=args.momentum, weight_decay=args.weight_decay)
上述代碼表示將模型Net網絡的 self.Conv1_2層的學習率設置為傳入學習率的10倍,base_params的學習沒有明確設置,則默認為傳入的學習率args.lr。
註意:
[{'params': base_params}, {'params': model.Conv1_2.parameters(), 'lr': 10 * args.lr}]
表示為列表中的字典結構。
這種方法設置不同的學習率顯得不夠靈活,可以為不同的層設置靈活的學習率,可以采用如下方法在adjust_learning_rate函數中設置:
def adjust_learning_rate(optimizer, epoch, args): lre = [] lre.extend([0.01] * 10) lre.extend([0.005] * 10) lre.extend([0.0025] * 10) lr = lre[epoch] optimizer.param_groups[0]['lr'] = 0.9 * lr optimizer.param_groups[1]['lr'] = 10 * lr print(param_group[0]['lr']) print(param_group[1]['lr'])
上述代碼中的optimizer.param_groups[0]就代表[{‘params’: base_params}, {‘params’: model.Conv1_2.parameters(), ‘lr’: 10 * args.lr}]中的’params’: base_params},optimizer.param_groups[1]代表{‘params’: model.Conv1_2.parameters(), ‘lr’: 10 * args.lr},這裡設置的學習率會把args.lr給覆蓋掉,個人認為上述代碼在設置學習率方面更靈活一些。上述代碼也可如下變成實現(註意學習率隨便設置的,未與上述代碼保持一致):
def adjust_learning_rate(optimizer, epoch, args): lre = np.logspace(-2, -4, 40) lr = lre[epoch] for i in range(len(optimizer.param_groups)): param_group = optimizer.param_groups[i] if i == 0: param_group['lr'] = 0.9 * lr else: param_group['lr'] = 10 * lr print(param_group['lr'])
下面貼出SGD優化器的PyTorch實現,及其每個參數的設置和表示意義,具體如下:
import torch from .optimizer import Optimizer, required class SGD(Optimizer): r"""Implements stochastic gradient descent (optionally with momentum). Nesterov momentum is based on the formula from `On the importance of initialization and momentum in deep learning`__. Args: params (iterable): iterable of parameters to optimize or dicts defining parameter groups lr (float): learning rate momentum (float, optional): momentum factor (default: 0) weight_decay (float, optional): weight decay (L2 penalty) (default: 0) dampening (float, optional): dampening for momentum (default: 0) nesterov (bool, optional): enables Nesterov momentum (default: False) Example: >>> optimizer = torch.optim.SGD(model.parameters(), lr=0.1, momentum=0.9) >>> optimizer.zero_grad() >>> loss_fn(model(input), target).backward() >>> optimizer.step() __ http://www.cs.toronto.edu/%7Ehinton/absps/momentum.pdf .. note:: The implementation of SGD with Momentum/Nesterov subtly differs from Sutskever et. al. and implementations in some other frameworks. Considering the specific case of Momentum, the update can be written as .. math:: v = \rho * v + g \\ p = p - lr * v where p, g, v and :math:`\rho` denote the parameters, gradient, velocity, and momentum respectively. This is in contrast to Sutskever et. al. and other frameworks which employ an update of the form .. math:: v = \rho * v + lr * g \\ p = p - v The Nesterov version is analogously modified. """ def __init__(self, params, lr=required, momentum=0, dampening=0, weight_decay=0, nesterov=False): if lr is not required and lr < 0.0: raise ValueError("Invalid learning rate: {}".format(lr)) if momentum < 0.0: raise ValueError("Invalid momentum value: {}".format(momentum)) if weight_decay < 0.0: raise ValueError("Invalid weight_decay value: {}".format(weight_decay)) defaults = dict(lr=lr, momentum=momentum, dampening=dampening, weight_decay=weight_decay, nesterov=nesterov) if nesterov and (momentum <= 0 or dampening != 0): raise ValueError("Nesterov momentum requires a momentum and zero dampening") super(SGD, self).__init__(params, defaults) def __setstate__(self, state): super(SGD, self).__setstate__(state) for group in self.param_groups: group.setdefault('nesterov', False) def step(self, closure=None): """Performs a single optimization step. Arguments: closure (callable, optional): A closure that reevaluates the model and returns the loss. """ loss = None if closure is not None: loss = closure() for group in self.param_groups: weight_decay = group['weight_decay'] momentum = group['momentum'] dampening = group['dampening'] nesterov = group['nesterov'] for p in group['params']: if p.grad is None: continue d_p = p.grad.data if weight_decay != 0: d_p.add_(weight_decay, p.data) if momentum != 0: param_state = self.state[p] if 'momentum_buffer' not in param_state: buf = param_state['momentum_buffer'] = torch.zeros_like(p.data) buf.mul_(momentum).add_(d_p) else: buf = param_state['momentum_buffer'] buf.mul_(momentum).add_(1 - dampening, d_p) if nesterov: d_p = d_p.add(momentum, buf) else: d_p = buf p.data.add_(-group['lr'], d_p) return loss
經驗總結:
在Fine-tuning時最好不要隔層設置層的參數的可學習與否,這樣做一般效果餅不理想,一般準則即可,即先Fine-tuning分類層,學習率設置的大一些,然後在將整個網絡設置一個較小的學習率,所有層一起訓練。
至於不先經過Fine-tune分類層,而是將整個網絡所有層一起訓練,隻是分類層的學習率相對設置大一些,這樣做也可以,至於哪個效果更好,沒評估過。當用三元組損失(triplet loss)微調用softmax loss訓練的網絡時,可以設置階梯型的較小學習率,整個網絡所有層一起訓練,效果比較好,而不用先Fine-tune分類層前一層的輸出。
以上為個人經驗,希望能給大傢一個參考,也希望大傢多多支持WalkonNet。
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