PixelPyramids: Exact Inference Models from Lossless Image Pyramids

This repository is the PyTorch implementation of the paper:

PixelPyramids: Exact Inference Models from Lossless Image Pyramids (ICCV 2021)

Shweta Mahajan and Stefan Roth

Requirements

The following code is written in Python 3.6.10 and CUDA 9.0.

Requirements:

• torch 1.7.1
• torchvision 0.8.2
• tqdm 4.58.0
• numpy 1.19.1

To install requirements:

conda config --add channels pytorch
conda config --add channels anaconda
conda config --add channels conda-forge
conda config --add channels conda-forge/label/cf202003
conda create -n <environment_name> --file requirements.txt
conda activate <environment_name>

Datasets

The datasets used in this project are:

• CelebA-HQ 256
• CelebA-HQ 1024
• LSUN-bedroom 128
• LSUN-church outdoor 128
• LSUN-tower 128
• ImageNet 128

Training

The important keyword arguments for training are,

• params_file : Path to the configuration file in the params folder.
• dataset_name : Name of the dataset. This can be found in the config files (params folder) of the different datasets.
• data_root : Path to the location of the dataset. Please see utils.py for default values.
• L : Number of levels in the pyramid decomposition.
• C : Number of channels for output of U-Net.
• n_bits : Number of bits for training the data.
• n_classes : List of the (number of mixture components) x 10. For each mixture component, 3 params for means, 3 params for coefficients, 3 params for logscales, 1 param for logits
• n_squeeze : List of number of squeeze operations per level.
• n_channels : Number of channels for the PixelCNNPP at the coarsest level.
• n_res_layers : Number of residual layers for the PixelCNNPP at the coarsest level.

Please follow the following instructions for training:

1. Train a model on CelebA-HQ-256,

   	python main.py --params_file './params/celeba_256.json' 

2. The model is evaluated after every epoch

Generation and Validation

Samples and test results in bits/dim can be obtained using main.py. Generated samples are stored in the ./samples folder. Download the checkpoints to the ckpts folder.

Memory requirements

The models were trained on four nvidia V100 GPU with 32 GB memory. The levels can be trained in parallel with a maximum of 24GB memory per level.

Results

Evaluation on different datasets

	bits/dim
CelebA-HQ_256	0.61
CelebA-HQ_1024	0.58
LSUN_bedroom_128	0.88
LSUN_church_128	1.07
LSUN_tower_128	0.95
ImageNet_128	3.40

Bibtex

@inproceedings{pixelpyramids21iccv,
  title     = {PixelPyramids: Exact Inference Models from Lossless Image Pyramids},
  author    = {Mahajan, Shweta and Roth, Stefan},
  booktitle = {Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV)},
  year = {2021}
}