Self-Supervised Learning (SSL)

Slideflow provides easy access to training the self-supervised, contrastive learning framework SimCLR. Self-supervised learning provides an avenue for learning useful visual representations in your dataset without requiring ground-truth labels. These visual representations can be exported as feature vectors and used for downstream analyses such as dimensionality reduction or multi-instance learning.

The slideflow.simclr module contains a forked Tensorflow implementation minimally modified to interface with Slideflow. SimCLR models can be trained with slideflow.Project.train_simclr(), and SimCLR features can be calculated as with other models using slideflow.Project.generate_features().

Training SimCLR

First, determine the SimCLR training parameters with slideflow.simclr.get_args(). This function accepts parameters via keyword arguments, such as learning_rate and temperature, and returns a configured slideflow.simclr.SimCLR_Args.

from slideflow import simclr

args = simclr.get_args(
    temperature=0.1,
    learning_rate=0.3,
    train_epochs=100,
    image_size=299
)

Next, assemble a training and (optionally) a validation dataset. The validation dataset is used to assess contrastive loss during training, but is not required.

import slideflow as sf

# Load a project and dataset
P = sf.load_project('path')
dataset = P.dataset(tile_px=299, tile_um=302)

# Split dataset into training/validation
train_dts, val_dts = dataset.split(
    val_fraction=0.3,
    model_type='classification',
    labels='subtype')

Finally, SimCLR can be trained with slideflow.Project.train_simclr(). You can train with a single dataset:

P.train_simclr(args, dataset)

You can train with an optional validation dataset:

P.train_simclr(
    args,
    train_dataset=train_dts,
    val_dataset=val_dts
)

And you can also optionally provide labels for training the supervised head. To train a supervised head, you’ll also need to set the SimCLR argument lineareval_while_pretraining=True.

# SimCLR args
args = simclr.get_args(
    ...,
    lineareval_while_pretraining=True
)

# Train with validation & supervised head
P.train_simclr(
    args,
    train_dataset=train_dts,
    val_dataset=val_dts,
    outcomes='subtype'
)

The SimCLR model checkpoints and final saved model will be saved in the simclr/ folder within the project root directory.

Training DINOv2

A lightly modified version of DINOv2 with Slideflow integration is available on GitHub. This version facilitates training DINOv2 with Slideflow datasets and adds stain augmentation to the training pipeline.

To train DINOv2, first install the package:

pip install git+https://github.com/jamesdolezal/dinov2.git

Next, configure the training parameters and datsets by providing a configuration YAML file. This configuration file should contain a slideflow section, which specifies the Slideflow project and dataset to use for training. An example YAML file is shown below:

train:
  dataset_path: slideflow
  batch_size_per_gpu: 32
  slideflow:
    project: "/mnt/data/projects/TCGA_THCA_BRAF"
    dataset:
      tile_px: 299
      tile_um: 302
      filters:
        brs_class:
        - "Braf-like"
        - "Ras-like"
    seed: 42
    outcome_labels: "brs_class"
    normalizer: "reinhard_mask"
    interleave_kwargs: null

See the DINOv2 README for more details on the configuration file format.

Finally, train DINOv2 using the same command-line interface as the original DINOv2 implementation. For example, to train DINOv2 on 4 GPUs on a single node:

torchrun --nproc_per_node=4 -m "dinov2.train.train" \
    --config-file /path/to/config.yaml \
    --output-dir /path/to/output_dir

The teacher weights will be saved in outdir/eval/.../teacher_checkpoint.pth, and the final configuration YAML will be saved in outdir/config.yaml.

Generating features

Generating features from a trained SSL is straightforward - use the same slideflow.Project.generate_features() and slideflow.DatasetFeatures interfaces as previously described, providing a path to a saved SimCLR model or checkpoint.

import slideflow as sf

# Create the SimCLR feature extractor
simclr = sf.build_feature_extractor(
    'simclr',
    ckpt='/path/to/simclr.ckpt'
)

# Calculate SimCLR features for a dataset
features = P.generate_features(simclr, ...)

For DINOv2 models, use 'dinov2' as the first argument, and pass the model configuration YAML file to cfg and the teacher checkpoint weights to weights.

dinov2 = build_feature_extractor(
    'dinov2',
    weights='/path/to/teacher_checkpoint.pth',
    cfg='/path/to/config.yaml'
)