User guide¶
As the name suggest, this package makes heavy use of PyTorch, so make sure you have it installed on your environment. It also relies on bob (and in particular for I/O and databases interfaces), so you may want to refer to their respective documentation as well. In particular, the following assumes that you have a conda environment with bob installed (see installation instructions) and that you cloned and built this package:
$ git clone git@gitlab.idiap.ch:bob/bob.learn.pytorch.git
$ cd bob.learn.pytorch
$ buildout
Anatomy of the package¶
This package is basically organized as follows (some files are omitted for clarity purposes):
bob/
+-- learn/
+-- pytorch/
+-- architectures/
+-- CNN8.py
+-- CASIANet.py
+-- ...
+-- datasets/
+-- casia_webface.py
+-- multipie.py
+-- ...
+-- scripts/
+-- train_cnn.py
+-- ...
+-- trainers/
+-- CNNTrainer.py
architecturescontains files defining the different network architectures. The network is defined as a derived class oftorch.nn.Moduleand must contain aforwardmethod. See for instance the simple examples provided in PyTorch documentation.datasetscontains files implementing datasets astorch.utils.data.Dataset. The dataset classes are meant to provide a bridge between bob’s databases (i.e.bob.db.*) and the dataset used by PyTorch. To see an example on how this could be achieved, have a look atbob/learn/pytorch/datasets/multipie.py. This directory also contains some utility functions, such as wrappers around some torchvision.transforms (note that this is needed since, some built-intorchvision.transformsignore the labels).scriptscontains the various scripts to perform training. More on that below.trainerscontains classes implementing training of networks. At the moment, there is only one trainer, which will train CNN for visual recognition. Note that the trainer may depend on the specific model (GANs, …).
Defining and training a network on an arbitrary dataset¶
Now let’s move to a concrete example. Let’s say that the goal is to train a simple network to perform face recognition on the AT&T database.
First, you’ll have to get the dataset, you can download it here. Assuming that you downloaded the zip archive in your current directory, do the following:
$ mkdir atnt
$ unzip att_faces.zip -d atnt/
$ rm atnt/README
The training script ./bin/train_cnn.py has a config file as argument.
The config file should specify at least the dataset and network variables (other parameters, such as the batch size could also be provided this way).
Let’s define the dataset: here we’ll define it directly in a config file, but you can of course implement it in a separate file and import it.
The following is heavily inspired by what is described in the PyTorch tutorial on data laoding and processing.
Have a look there for more details.
import os
import numpy
# load images
import bob.io.base
import bob.io.image
# to build your dataset
from torch.utils.data import Dataset
# mainly use to compose transforms (i.e. apply more than one transform to an input image)
import torchvision.transforms as transforms
# wrapper around torchvision.transforms
# turns out that the original ones are 'destroying' labels ...
from bob.learn.pytorch.datasets import ToTensor
from bob.learn.pytorch.datasets import Normalize
from bob.learn.pytorch.datasets import Resize
# to get the right number of classes (between 0 and n_classes)
from bob.learn.pytorch.datasets.utils import map_labels
class AtntDataset(Dataset):
""" Class defining the AT&T face dataset as a PyTorch Dataset
Attributes
----------
root_dir: str
The path to the raw images.
transform: :py:mod:`torchvision.transforms`
The transfrom to apply to the input image
data_files: list(str)
The list of image files.
id_labels: list(int)
The subjects' identity, for each file
"""
def __init__(self, root_dir, transform=None):
""" Init method
Parameters
----------
root_dir: str
The path to the raw images.
transform: :py:mod:`torchvision.transforms`
The transfrom to apply to the input image
"""
self.root_dir = root_dir
self.transform = transform
self.data_files = []
id_labels = []
for root, dirs, files in os.walk(self.root_dir):
for name in files:
filename = os.path.split(os.path.join(root, name))[-1]
path = root.split(os.sep)
subject = int(path[-1].replace('s', ''))
self.data_files.append(os.path.join(root, name))
id_labels.append(subject)
self.id_labels = map_labels(id_labels)
def __len__(self):
""" Return the length of the dataset (i.e. nb of examples)
"""
return len(self.data_files)
def __getitem__(self, idx):
""" Return a sample from the dataset
The sample consists in an image and a label (i.e. a face and an ID)
"""
image = bob.io.base.load(self.data_files[idx])
# add an empty dimension so that the array is HxWxC (as expected by PyTorch)
image = image[..., numpy.newaxis]
identity = self.id_labels[idx]
sample = {'image': image, 'label': identity}
# apply transform
if self.transform:
sample = self.transform(sample)
return sample
# instantiate the dataset
dataset = AtntDataset(root_dir='./atnt',
transform=transforms.Compose([
Resize((32, 32)),
ToTensor(),
Normalize((0.5,), (0.5,))
])
)
Now that we have a dataset, we should define a network. Again, we’ll do it directly in the configuration file, but
you can also define it in architectures and import it in your configuration. For the sake of simplicity, the
architecture is directly taken from PyTorch tutorials.
Note the slight modification at the end of the forward method: it returns both the ouput (out) and the
embedding x (which may be used as a features to describe an identity).
import torch
import torch.nn as nn
import torch.nn.functional as F
class Net(nn.Module):
def __init__(self):
super(Net, self).__init__()
self.conv1 = nn.Conv2d(1, 6, 5)
self.conv2 = nn.Conv2d(6, 16, 5)
self.fc1 = nn.Linear(16 * 5 * 5, 120)
self.fc2 = nn.Linear(120, 84)
self.fc3 = nn.Linear(84, 40)
def forward(self, x):
x = F.max_pool2d(F.relu(self.conv1(x)), (2, 2))
x = F.max_pool2d(F.relu(self.conv2(x)), 2)
x = x.view(-1, self.num_flat_features(x))
x = F.relu(self.fc1(x))
x = F.relu(self.fc2(x))
out = self.fc3(x)
return out, x
def num_flat_features(self, x):
size = x.size()[1:]
num_features = 1
for s in size:
num_features *= s
return num_features
# instantiate the network
network = Net()
Since we have both a dataset and a network define in a configuration file, we can now train the network using the dataset. This is done by launching the following script on your terminal:
$ ./bin/train_cnn config.py -vvv
And the output should look like this:
bob.learn.pytorch@2018-05-16 10:10:47,582 -- DEBUG: Model file = None
bob.learn.pytorch@2018-05-16 10:10:47,582 -- DEBUG: Batch size = 64
bob.learn.pytorch@2018-05-16 10:10:47,582 -- DEBUG: Epochs = 2
bob.learn.pytorch@2018-05-16 10:10:47,583 -- DEBUG: Learning rate = 0.01
bob.learn.pytorch@2018-05-16 10:10:47,583 -- DEBUG: Seed = 3
bob.learn.pytorch@2018-05-16 10:10:47,583 -- DEBUG: Output directory = training
bob.learn.pytorch@2018-05-16 10:10:47,583 -- DEBUG: Use GPU = False
bob.learn.pytorch@2018-05-16 10:10:47,589 -- INFO: There are 400 training images from 39 categories
bob.learn.pytorch@2018-05-16 10:10:47,589 -- INFO: Starting training from scratch
bob.learn.pytorch@2018-05-16 10:10:47,851 -- INFO: [0/2][0/7] => Loss = 3.6826722621917725 (time spent: 0.11152887344360352)
bob.learn.pytorch@2018-05-16 10:10:48,010 -- INFO: [0/2][1/7] => Loss = 3.7005279064178467 (time spent: 0.01898503303527832)
bob.learn.pytorch@2018-05-16 10:10:48,165 -- INFO: [0/2][2/7] => Loss = 3.6845760345458984 (time spent: 0.014686822891235352)
bob.learn.pytorch@2018-05-16 10:10:48,337 -- INFO: [0/2][3/7] => Loss = 3.698812246322632 (time spent: 0.01413273811340332)
bob.learn.pytorch@2018-05-16 10:10:48,479 -- INFO: [0/2][4/7] => Loss = 3.6925580501556396 (time spent: 0.013530492782592773)
bob.learn.pytorch@2018-05-16 10:10:48,731 -- INFO: [0/2][5/7] => Loss = 3.6884894371032715 (time spent: 0.015494346618652344)
bob.learn.pytorch@2018-05-16 10:10:48,839 -- INFO: [0/2][6/7] => Loss = 3.701101303100586 (time spent: 0.008399486541748047)
bob.learn.pytorch@2018-05-16 10:10:48,839 -- INFO: EPOCH 1 DONE
bob.learn.pytorch@2018-05-16 10:10:48,839 -- INFO: Saving model to training/model_1_0.pth
bob.learn.pytorch@2018-05-16 10:10:49,084 -- INFO: [1/2][0/7] => Loss = 3.6887857913970947 (time spent: 0.01661086082458496)
bob.learn.pytorch@2018-05-16 10:10:49,470 -- INFO: [1/2][1/7] => Loss = 3.690291404724121 (time spent: 0.20917153358459473)
bob.learn.pytorch@2018-05-16 10:10:49,653 -- INFO: [1/2][2/7] => Loss = 3.690778970718384 (time spent: 0.018873929977416992)
bob.learn.pytorch@2018-05-16 10:10:49,814 -- INFO: [1/2][3/7] => Loss = 3.7087666988372803 (time spent: 0.015717029571533203)
bob.learn.pytorch@2018-05-16 10:10:50,022 -- INFO: [1/2][4/7] => Loss = 3.684515953063965 (time spent: 0.02263784408569336)
bob.learn.pytorch@2018-05-16 10:10:50,253 -- INFO: [1/2][5/7] => Loss = 3.6845874786376953 (time spent: 0.014308452606201172)
bob.learn.pytorch@2018-05-16 10:10:50,306 -- INFO: [1/2][6/7] => Loss = 3.6927332878112793 (time spent: 0.008508920669555664)
bob.learn.pytorch@2018-05-16 10:10:50,306 -- INFO: EPOCH 2 DONE
bob.learn.pytorch@2018-05-16 10:10:50,306 -- INFO: Saving model to training/model_2_0.pth
Congrats ! You have successfully train your first model (it is meaningless though …).
A more realistic example¶
Note
For this example to work, you should first download the CASIA Webface database, detect, crop and resize color face images to 128x128 …
Imagine now that you want to try and reproduce what is described in the following article:
@Misc{yi-arxiv-2014,
Author = {Yi, D. and Lei, Z. and Liao, S. and Li, S.Z.},
Title = {Learning Face Representation From Scratch},
eprint = {arXiv:1411.7923},
year = 2014
}
Your configuration file casia.py should look like:
### DATA ###
from bob.learn.pytorch.datasets import CasiaWebFaceDataset
import torchvision.transforms as transforms
from bob.learn.pytorch.datasets import RollChannels
from bob.learn.pytorch.datasets import ToTensor
from bob.learn.pytorch.datasets import Normalize
dataset = CasiaWebFaceDataset(root_dir='/path-to-your-cropped-faces-images',
transform=transforms.Compose([
RollChannels(),
ToTensor(),
Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))
])
)
### NETWORK ###
from bob.learn.pytorch.architectures import CASIANet
number_of_classes = 10575
dropout = 0.5
network = CASIANet(number_of_classes, dropout)
Then, you can lauch the trainin script (and leave it running for one week or so …)
$ ./bin/train_cnn casia.py -vvv