.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "beginner/transfer_learning_tutorial.py" .. LINE NUMBERS ARE GIVEN BELOW. .. only:: html .. note:: :class: sphx-glr-download-link-note Click :ref:`here ` to download the full example code .. rst-class:: sphx-glr-example-title .. _sphx_glr_beginner_transfer_learning_tutorial.py: Transfer Learning for Computer Vision Tutorial ============================================== **Author**: `Sasank Chilamkurthy `_ In this tutorial, you will learn how to train a convolutional neural network for image classification using transfer learning. You can read more about the transfer learning at `cs231n notes `__ Quoting these notes, In practice, very few people train an entire Convolutional Network from scratch (with random initialization), because it is relatively rare to have a dataset of sufficient size. Instead, it is common to pretrain a ConvNet on a very large dataset (e.g. ImageNet, which contains 1.2 million images with 1000 categories), and then use the ConvNet either as an initialization or a fixed feature extractor for the task of interest. These two major transfer learning scenarios look as follows: - **Finetuning the ConvNet**: Instead of random initialization, we initialize the network with a pretrained network, like the one that is trained on imagenet 1000 dataset. Rest of the training looks as usual. - **ConvNet as fixed feature extractor**: Here, we will freeze the weights for all of the network except that of the final fully connected layer. This last fully connected layer is replaced with a new one with random weights and only this layer is trained. .. GENERATED FROM PYTHON SOURCE LINES 33-53 .. code-block:: default # License: BSD # Author: Sasank Chilamkurthy import torch import torch.nn as nn import torch.optim as optim from torch.optim import lr_scheduler import torch.backends.cudnn as cudnn import numpy as np import torchvision from torchvision import datasets, models, transforms import matplotlib.pyplot as plt import time import os from PIL import Image from tempfile import TemporaryDirectory cudnn.benchmark = True plt.ion() # interactive mode .. rst-class:: sphx-glr-script-out .. code-block:: none .. GENERATED FROM PYTHON SOURCE LINES 54-73 Load Data --------- We will use torchvision and torch.utils.data packages for loading the data. The problem we're going to solve today is to train a model to classify **ants** and **bees**. We have about 120 training images each for ants and bees. There are 75 validation images for each class. Usually, this is a very small dataset to generalize upon, if trained from scratch. Since we are using transfer learning, we should be able to generalize reasonably well. This dataset is a very small subset of imagenet. .. Note :: Download the data from `here `_ and extract it to the current directory. .. GENERATED FROM PYTHON SOURCE LINES 73-107 .. code-block:: default # Data augmentation and normalization for training # Just normalization for validation data_transforms = { 'train': transforms.Compose([ transforms.RandomResizedCrop(224), transforms.RandomHorizontalFlip(), transforms.ToTensor(), transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225]) ]), 'val': transforms.Compose([ transforms.Resize(256), transforms.CenterCrop(224), transforms.ToTensor(), transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225]) ]), } data_dir = 'data/hymenoptera_data' image_datasets = {x: datasets.ImageFolder(os.path.join(data_dir, x), data_transforms[x]) for x in ['train', 'val']} dataloaders = {x: torch.utils.data.DataLoader(image_datasets[x], batch_size=4, shuffle=True, num_workers=4) for x in ['train', 'val']} dataset_sizes = {x: len(image_datasets[x]) for x in ['train', 'val']} class_names = image_datasets['train'].classes # We want to be able to train our model on an `accelerator `__ # such as CUDA, MPS, MTIA, or XPU. If the current accelerator is available, we will use it. Otherwise, we use the CPU. device = torch.accelerator.current_accelerator().type if torch.accelerator.is_available() else "cpu" print(f"Using {device} device") .. rst-class:: sphx-glr-script-out .. code-block:: none Using cpu device .. GENERATED FROM PYTHON SOURCE LINES 108-112 Visualize a few images ^^^^^^^^^^^^^^^^^^^^^^ Let's visualize a few training images so as to understand the data augmentations. .. GENERATED FROM PYTHON SOURCE LINES 112-135 .. code-block:: default def imshow(inp, title=None): """Display image for Tensor.""" inp = inp.numpy().transpose((1, 2, 0)) mean = np.array([0.485, 0.456, 0.406]) std = np.array([0.229, 0.224, 0.225]) inp = std * inp + mean inp = np.clip(inp, 0, 1) plt.imshow(inp) if title is not None: plt.title(title) plt.pause(0.001) # pause a bit so that plots are updated # Get a batch of training data inputs, classes = next(iter(dataloaders['train'])) # Make a grid from batch out = torchvision.utils.make_grid(inputs) imshow(out, title=[class_names[x] for x in classes]) .. image-sg:: /beginner/images/sphx_glr_transfer_learning_tutorial_001.png :alt: ['bees', 'ants', 'ants', 'bees'] :srcset: /beginner/images/sphx_glr_transfer_learning_tutorial_001.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 136-147 Training the model ------------------ Now, let's write a general function to train a model. Here, we will illustrate: - Scheduling the learning rate - Saving the best model In the following, parameter ``scheduler`` is an LR scheduler object from ``torch.optim.lr_scheduler``. .. GENERATED FROM PYTHON SOURCE LINES 147-220 .. code-block:: default def train_model(model, criterion, optimizer, scheduler, num_epochs=25): since = time.time() # Create a temporary directory to save training checkpoints with TemporaryDirectory() as tempdir: best_model_params_path = os.path.join(tempdir, 'best_model_params.pt') torch.save(model.state_dict(), best_model_params_path) best_acc = 0.0 for epoch in range(num_epochs): print(f'Epoch {epoch}/{num_epochs - 1}') print('-' * 10) # Each epoch has a training and validation phase for phase in ['train', 'val']: if phase == 'train': model.train() # Set model to training mode else: model.eval() # Set model to evaluate mode running_loss = 0.0 running_corrects = 0 # Iterate over data. for inputs, labels in dataloaders[phase]: inputs = inputs.to(device) labels = labels.to(device) # zero the parameter gradients optimizer.zero_grad() # forward # track history if only in train with torch.set_grad_enabled(phase == 'train'): outputs = model(inputs) _, preds = torch.max(outputs, 1) loss = criterion(outputs, labels) # backward + optimize only if in training phase if phase == 'train': loss.backward() optimizer.step() # statistics running_loss += loss.item() * inputs.size(0) running_corrects += torch.sum(preds == labels.data) if phase == 'train': scheduler.step() epoch_loss = running_loss / dataset_sizes[phase] epoch_acc = running_corrects.double() / dataset_sizes[phase] print(f'{phase} Loss: {epoch_loss:.4f} Acc: {epoch_acc:.4f}') # deep copy the model if phase == 'val' and epoch_acc > best_acc: best_acc = epoch_acc torch.save(model.state_dict(), best_model_params_path) print() time_elapsed = time.time() - since print(f'Training complete in {time_elapsed // 60:.0f}m {time_elapsed % 60:.0f}s') print(f'Best val Acc: {best_acc:4f}') # load best model weights model.load_state_dict(torch.load(best_model_params_path, weights_only=True)) return model .. GENERATED FROM PYTHON SOURCE LINES 221-226 Visualizing the model predictions ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Generic function to display predictions for a few images .. GENERATED FROM PYTHON SOURCE LINES 226-253 .. code-block:: default def visualize_model(model, num_images=6): was_training = model.training model.eval() images_so_far = 0 fig = plt.figure() with torch.no_grad(): for i, (inputs, labels) in enumerate(dataloaders['val']): inputs = inputs.to(device) labels = labels.to(device) outputs = model(inputs) _, preds = torch.max(outputs, 1) for j in range(inputs.size()[0]): images_so_far += 1 ax = plt.subplot(num_images//2, 2, images_so_far) ax.axis('off') ax.set_title(f'predicted: {class_names[preds[j]]}') imshow(inputs.cpu().data[j]) if images_so_far == num_images: model.train(mode=was_training) return model.train(mode=was_training) .. GENERATED FROM PYTHON SOURCE LINES 254-259 Finetuning the ConvNet ---------------------- Load a pretrained model and reset final fully connected layer. .. GENERATED FROM PYTHON SOURCE LINES 259-276 .. code-block:: default model_ft = models.resnet18(weights='IMAGENET1K_V1') num_ftrs = model_ft.fc.in_features # Here the size of each output sample is set to 2. # Alternatively, it can be generalized to ``nn.Linear(num_ftrs, len(class_names))``. model_ft.fc = nn.Linear(num_ftrs, 2) model_ft = model_ft.to(device) criterion = nn.CrossEntropyLoss() # Observe that all parameters are being optimized optimizer_ft = optim.SGD(model_ft.parameters(), lr=0.001, momentum=0.9) # Decay LR by a factor of 0.1 every 7 epochs exp_lr_scheduler = lr_scheduler.StepLR(optimizer_ft, step_size=7, gamma=0.1) .. rst-class:: sphx-glr-script-out .. code-block:: none Downloading: "https://download.pytorch.org/models/resnet18-f37072fd.pth" to /var/lib/ci-user/.cache/torch/hub/checkpoints/resnet18-f37072fd.pth 0%| | 0.00/44.7M [00:00`__. .. GENERATED FROM PYTHON SOURCE LINES 304-325 .. code-block:: default model_conv = torchvision.models.resnet18(weights='IMAGENET1K_V1') for param in model_conv.parameters(): param.requires_grad = False # Parameters of newly constructed modules have requires_grad=True by default num_ftrs = model_conv.fc.in_features model_conv.fc = nn.Linear(num_ftrs, 2) model_conv = model_conv.to(device) criterion = nn.CrossEntropyLoss() # Observe that only parameters of final layer are being optimized as # opposed to before. optimizer_conv = optim.SGD(model_conv.fc.parameters(), lr=0.001, momentum=0.9) # Decay LR by a factor of 0.1 every 7 epochs exp_lr_scheduler = lr_scheduler.StepLR(optimizer_conv, step_size=7, gamma=0.1) .. GENERATED FROM PYTHON SOURCE LINES 326-333 Train and evaluate ^^^^^^^^^^^^^^^^^^ On CPU this will take about half the time compared to previous scenario. This is expected as gradients don't need to be computed for most of the network. However, forward does need to be computed. .. GENERATED FROM PYTHON SOURCE LINES 333-337 .. code-block:: default model_conv = train_model(model_conv, criterion, optimizer_conv, exp_lr_scheduler, num_epochs=25) .. rst-class:: sphx-glr-script-out .. code-block:: none Epoch 0/24 ---------- train Loss: 0.5269 Acc: 0.7295 val Loss: 0.3301 Acc: 0.8627 Epoch 1/24 ---------- train Loss: 0.4728 Acc: 0.7869 val Loss: 0.1882 Acc: 0.9346 Epoch 2/24 ---------- train Loss: 0.5078 Acc: 0.7910 val Loss: 0.2336 Acc: 0.9085 Epoch 3/24 ---------- train Loss: 0.4478 Acc: 0.7951 val Loss: 0.6025 Acc: 0.7843 Epoch 4/24 ---------- train Loss: 0.5025 Acc: 0.7582 val Loss: 0.1724 Acc: 0.9477 Epoch 5/24 ---------- train Loss: 0.4349 Acc: 0.7746 val Loss: 0.2675 Acc: 0.9020 Epoch 6/24 ---------- train Loss: 0.4907 Acc: 0.8074 val Loss: 0.1820 Acc: 0.9412 Epoch 7/24 ---------- train Loss: 0.3584 Acc: 0.8443 val Loss: 0.1775 Acc: 0.9477 Epoch 8/24 ---------- train Loss: 0.3461 Acc: 0.8443 val Loss: 0.1663 Acc: 0.9412 Epoch 9/24 ---------- train Loss: 0.3435 Acc: 0.8320 val Loss: 0.1812 Acc: 0.9542 Epoch 10/24 ---------- train Loss: 0.3565 Acc: 0.8484 val Loss: 0.1746 Acc: 0.9542 Epoch 11/24 ---------- train Loss: 0.3739 Acc: 0.8361 val Loss: 0.1782 Acc: 0.9346 Epoch 12/24 ---------- train Loss: 0.3544 Acc: 0.8607 val Loss: 0.1979 Acc: 0.9346 Epoch 13/24 ---------- train Loss: 0.4074 Acc: 0.8320 val Loss: 0.1600 Acc: 0.9412 Epoch 14/24 ---------- train Loss: 0.3483 Acc: 0.8402 val Loss: 0.1785 Acc: 0.9281 Epoch 15/24 ---------- train Loss: 0.3430 Acc: 0.8730 val Loss: 0.1811 Acc: 0.9477 Epoch 16/24 ---------- train Loss: 0.3852 Acc: 0.8279 val Loss: 0.1902 Acc: 0.9477 Epoch 17/24 ---------- train Loss: 0.4035 Acc: 0.7992 val Loss: 0.1599 Acc: 0.9412 Epoch 18/24 ---------- train Loss: 0.3891 Acc: 0.8238 val Loss: 0.1866 Acc: 0.9477 Epoch 19/24 ---------- train Loss: 0.3276 Acc: 0.8607 val Loss: 0.1816 Acc: 0.9412 Epoch 20/24 ---------- train Loss: 0.3562 Acc: 0.8484 val Loss: 0.1835 Acc: 0.9412 Epoch 21/24 ---------- train Loss: 0.2691 Acc: 0.8934 val Loss: 0.1633 Acc: 0.9477 Epoch 22/24 ---------- train Loss: 0.3320 Acc: 0.8484 val Loss: 0.1932 Acc: 0.9346 Epoch 23/24 ---------- train Loss: 0.3173 Acc: 0.8525 val Loss: 0.1837 Acc: 0.9412 Epoch 24/24 ---------- train Loss: 0.3681 Acc: 0.8238 val Loss: 0.1849 Acc: 0.9412 Training complete in 2m 16s Best val Acc: 0.954248 .. GENERATED FROM PYTHON SOURCE LINES 339-346 .. code-block:: default visualize_model(model_conv) plt.ioff() plt.show() .. image-sg:: /beginner/images/sphx_glr_transfer_learning_tutorial_003.png :alt: predicted: bees, predicted: bees, predicted: ants, predicted: bees, predicted: ants, predicted: ants :srcset: /beginner/images/sphx_glr_transfer_learning_tutorial_003.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 347-353 Inference on custom images -------------------------- Use the trained model to make predictions on custom images and visualize the predicted class labels along with the images. .. GENERATED FROM PYTHON SOURCE LINES 353-374 .. code-block:: default def visualize_model_predictions(model,img_path): was_training = model.training model.eval() img = Image.open(img_path) img = data_transforms['val'](img) img = img.unsqueeze(0) img = img.to(device) with torch.no_grad(): outputs = model(img) _, preds = torch.max(outputs, 1) ax = plt.subplot(2,2,1) ax.axis('off') ax.set_title(f'Predicted: {class_names[preds[0]]}') imshow(img.cpu().data[0]) model.train(mode=was_training) .. GENERATED FROM PYTHON SOURCE LINES 376-386 .. code-block:: default visualize_model_predictions( model_conv, img_path='data/hymenoptera_data/val/bees/72100438_73de9f17af.jpg' ) plt.ioff() plt.show() .. image-sg:: /beginner/images/sphx_glr_transfer_learning_tutorial_004.png :alt: Predicted: bees :srcset: /beginner/images/sphx_glr_transfer_learning_tutorial_004.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 387-394 Further Learning ----------------- If you would like to learn more about the applications of transfer learning, checkout our `Quantized Transfer Learning for Computer Vision Tutorial `_. .. rst-class:: sphx-glr-timing **Total running time of the script:** ( 7 minutes 3.966 seconds) .. _sphx_glr_download_beginner_transfer_learning_tutorial.py: .. only:: html .. container:: sphx-glr-footer sphx-glr-footer-example .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: transfer_learning_tutorial.py ` .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: transfer_learning_tutorial.ipynb ` .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_