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Generative Modeling with Flow-Guided Density Ratio Learning

preprint License: MIT Venue:ECML/PKDD 2024


Left: Illustration of FDRL's training setup for the tau training iteration. For clarity, we emphasize the choices of the f-divergence and g, the Bregman divergence function, as part of training. Right: the various applications of FDRL, ranging from unconditional image generation to class-conditional generation by composition with external classifiers and unpaired image-to-image translation.

Full Paper with Supplementary Material

You can find the full paper here or on arXiv as linked above.

Setup

There are a few setup steps to run through before we can start training and evaluating models.

  1. Install the relevant libraries. As the code was developed using Python 3.8, it is recommended to use an environment with the same Python version.
conda create -n <env name> python=3.8 # using conda environments is optional but highly recommended
conda activate <env name>
pip install -r requirements.txt
  1. Next we need to generated the data-dependent prior distributions for the relevant datasets, as well as FID statistics for use in evaluation for CIFAR10 and CelebA.
python dataset_setup.py --data_dir <path/to/dataset> --dataset <cifar10/celeba/lsun_church> --device <eg: cuda:0, cpu>

See the argparse comments in dataset_setup.py for more details. This process will create a file <dataset>_ddp.pt, which is a multivariate Gaussian fitted to the dataset. For CIFAR10/CelebA, it additionally creates a file eval/<dataset>_stats.npz, which contains the necessary statistics for FID calculation during evaluation.

Datasets

  1. CIFAR10: downloaded automatically with PyTorch's torchvision.datasets.CIFAR10 when executing training code.
  2. CelebA: either automatically with torchvision.datasets.CelebA (which can be unreliable) or with instructions from the official webpage.
  3. LSUN: refer to instructions from the official Github.
  4. Cat2dog: refer to instructions from the DRIT Github.

Training

Training configs can be changed in the configs/<dataset>.yaml files. Crucially, you might wish to change the entries data_dir and device, which corresponds to where the dataset is stored, and which device(s) to use for training. You can vary the choices of Bregman divergence and f-divergences in the entries loss_function and f_divergence. use_wandb is an optional setting you can set to true if you wish to track your runs using Weights and Biases.

Unconditional Generation (DDP)

To train a model with the data-dependent prior, run

python train_ddp.py --config ./configs/<dataset>.yaml # for cifar10, celeba and lsun_church only

Training results are stored in a data and timestamped folder in results/<dataset>. A model checkpoint will be saved under the ckpt folder every save_steps iterations as specified in the config, and samples from the model are plotted in logs every log_steps iterations.

Image-to-image Translation

Image-to-image translation models can be trained in same way by running

python train_im2im_translation.py --config ./configs/cat2dog.yaml --device <cuda:0, cuda:1 etc>

Evaluation

Unconditional Generation and FID Scores

To evaluate the model for unconditional generation using DDP, run

python eval_ddp.py --ckpt <path/to/checkpoint> --device <cuda:0, cuda:1 etc>

It will save some samples of generated images in the samples folder. For CIFAR10 and CelebA, this will generate 50K images and compare the activation statistcs of the pool3 layer in the InceptionV3 network with those calculated when running eval_setup.py earlier.

Conditional Generation

To convert an unconditional model to a class-conditional generator, you will first need to download the pretrained robust classifier from robustness Github page, specifically the CIFAR10 L2-norm ResNet50 ε = 1.0. Do note that with Python 3.8, you will get an error when loading this model checkpoint as seen by this issue. You can resolve this by running this whole project in Python 3.7 (but I have not tested if everything works in 3.7), or follow the linked issue: only load and resave the model in Python 3.7, the resultant checkpoint should work in 3.8.

After you have done so, you can perform conditional generation by using your CIFAR10 LR-KL checkpoint with the instructions in the class_conditional_flow.ipynb. The hyperparameters in the notebook are tuned only for LR-KL, so attempts with other models may produce different results.

Image-to-image Translation

To run some test examples for image-to-image translation on the Cat2dog dataset, simply follow the instructions in the eval_im2im_translation.ipynb notebook.

Pretrained Checkpoints

Checkpoints available under releases.

Contact

If you have any questions regarding the code or the paper, please email Alvin.

BibTeX

If you find this repository or the ideas presented in our paper useful, please consider citing.

@article{heng2023generative,
  title={Generative Modeling with Flow-Guided Density Ratio Learning},
  author={Heng, Alvin and Ansari, Abdul Fatir and Soh, Harold},
  journal={arXiv preprint arXiv:2303.03714},
  year={2023}
}