Accelerating Diffusion Models via Early Stop of the Diffusion Process

This repo intends to release code for our work:

Zhaoyang Lyu, Xudong XU, Ceyuan Yang, Dahua Lin, Bo Dai"Accelerating Diffusion Models via Early Stop of the Diffusion Process".

We propose the Early-Stopped Denoising Diffusion Probabilistic Model (ES-DDPM) that accelerates the training and sampling process of DDPMs by adopting early stop in the diffusion process. ES-DDPM can combine a pre-trained DDPM with another pre-trained generative model such as a VAE or GAN to form a new generative model. The combined generative model can outperform the original DDPM in terms of both sample quality and sampling speed. Below is a comparison between ES-DDPM and vanilla DDPM.

Acknowledgement

This repo is based on the open-source repo for Guided Diffusion.

Set up the environment

The code is tested with Pytorch 1.11.0 and CUDA 11.3. Run the following command to install dependencies and the guided-diffusion package:

bash setup_env.sh
pip install -e .

Download Checkpoints and Data

We use pre-trained DDPMs and GAN-generated images from the repo Guided Diffusion. Download pretrained DDPMs on ImageNet-64, LSUN-Bedroom-256, LSUN-Cat-256 from this page. Move the ImageNet DDPM checkpoint to the folder scripts/models, and move LSUN DDPM checkpoints to the folder scripts/models/lsun.

Then download pre-generated ImageNet-64 (BigGAN-deep),
LSUN-Bedroom (StyleGAN) and LSUN-Cat (StyleGAN2) images from this page. Move ImageNet pre-generated images to the folder evaluations/precomputed, and move LSUN pre-generated images to the folder evaluations/precomputed/lsun.

Finally, download the reference batches for FID and other metric evaluations from this page. Download the ImageNet reference batch and move it to the folder evaluations/precomputed. Download the LSUN-Bedroom reference batch and LSUN-Cat reference batch, and move them to the folder evaluations/precomputed/lsun.

Sampling Images from ES-DDPMs

cd scripts

Run the following command to use ES-DDPM (T'=100, DDPM combined with BigGAN-deep) to generate ImageNet-64 images (with jumping interval 4):

python generate_processes_diffusion_and_reverse.py --classifier_guidance_scale 0 --reverse_steps 25 --chain_length 250 --dataset imagenet64 --dataset_path ../evaluations/precomputed/biggan_deep_imagenet64.npz --devices '0,1,2,3,4,5,6,7' --execute

Run the following command to use ES-DDPM (T'=100, DDPM combined with StyleGAN) to generate LSUN-Bedroom-256 images:

python generate_processes_diffusion_and_reverse.py --reverse_steps 100 --chain_length 1000 --dataset lsun_bedroom --dataset_path ../evaluations/precomputed/lsun/stylegan_lsun_bedroom.npz --devices '0,1,2,3,4,5,6,7' --execute

Run the following command to use ES-DDPM (T'=100, DDPM combined with StyleGAN2) to generate LSUN-Cat-256 images:

python generate_processes_diffusion_and_reverse.py --reverse_steps 100 --chain_length 1000 --dataset lsun_cat --dataset_path ../evaluations/precomputed/lsun/stylegan2_lsun_cat.npz --devices '0,1,2,3,4,5,6,7' --execute

If you want to use a different T' value, you can set the argument reverse_steps to the corresponding value.

Couple ES-DDPM with Timestep-Respacing and DDIM

As stated in our paper, ES-DDPM can be coupled with other DDPM acceleration methods to achieve further acceleration. We use Timestep-Respacing and DDIM as an illustration in our experiments. Both Timestep-Respacing and DDIM allows us to sampling from a pre-trained ES-DDPM only on a subsequence of the original T' denoising steps. We choose a uniform subsequence in our T' denoising steps with jumping interval N.

To couple ES-DDPM with Timestep-Respacing, you only need to change the arguments chain_length and reverse_steps in the above sampling commands. Specifically, if you want to sampling from ES-DDPM with jumping interval N, you need to set chain_length to 1000/N, and set reverse_steps to T'/N.

For example, run the following command to use ES-DDPM (T'=100, DDPM combined with StyleGAN) to generate LSUN-Bedroom-256 images with a jumping interval 5:

python generate_processes_diffusion_and_reverse.py --reverse_steps 20 --chain_length 200 --dataset lsun_bedroom --dataset_path ../evaluations/precomputed/lsun/stylegan_lsun_bedroom.npz --devices '0,1,2,3,4,5,6,7' --execute

If you want to use DDIM for sampling, simply add the text ddim to the beginning of the argument chain_length: