Denoising Diffusion Implicit Models
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "arXiv — non-exclusive license to distribute" does not allow redistributing the text itself. Original — arxiv.org/pdf/2010.02502
Summary
Diffusion-based image generators such as DDPM produce samples rivaling GANs, but generation is very slow because the reverse chain must run through every step of a long noising process, typically T = 1000. The authors propose DDIM, which keeps the DDPM training procedure but changes how samples are drawn. They note that the DDPM loss depends only on per-step marginals of the noising process, not on its full joint distribution. This lets them build a family of non-Markovian forward processes, controlled by a variance parameter σ, that share the same surrogate objective. Setting σ to zero gives a deterministic, implicit generator that can skip timesteps and sample along a short sub-sequence. A model trained once as a DDPM can therefore be reused without retraining. On CIFAR10, CelebA and LSUN, DDIM keeps sample quality much better than DDPM when steps are cut sharply, achieving 10× to 50× wall-clock speedups. Its deterministic latent mapping also enables meaningful interpolation and accurate reconstruction, which makes diffusion models far more practical.
Key points
- Motivating cost: drawing 50k 32×32 images from a DDPM takes about 20 hours on an Nvidia 2080 Ti, while a GAN needs under a minute. At 256×256 resolution, the DDPM time approaches 1000 hours.
- Theorem 1: for every σ > 0, the variational objective J_σ equals a weighted DDPM loss L_γ up to a constant. The parameter η interpolates between deterministic DDIM (η = 0) and DDPM-like sampling (η = 1).
- Experimental setup: experiments use CIFAR10 (32×32), CelebA (64×64), LSUN Bedroom and LSUN Church (both 256×256). The models are pretrained DDPM U-Net (Wide ResNet) checkpoints, except CelebA, which the authors trained themselves.
- Results with 20 sampling steps (FID):
- LSUN Bedroom: DDIM 8.89 vs DDPM 22.77.
- LSUN Church: DDIM 12.47 vs DDPM 23.37.
- For reference, 1000-step DDPM scores 6.36 (Bedroom) and 7.89 (Church).
- At 100 steps on Church, DDPM is slightly better (8.27 vs 10.58).
- Consistency: the same initial x_T yields images with similar high-level features regardless of chain length. Spherical linear interpolation (slerp) of x_T values produces smooth semantic interpolations.
Cited by
- Structured Denoising Diffusion Models in Discrete State-Spaces
- RAFT: Reward rAnked FineTuning for Generative Foundation Model Alignment
- Flow Matching for Generative Modeling
- Flow Straight and Fast: Learning to Generate and Transfer Data with Rectified Flow
- SDXL: Improving Latent Diffusion Models for High-Resolution Image Synthesis
- Hierarchical Text-Conditional Image Generation with CLIP Latents
- Photorealistic Text-to-Image Diffusion Models with Deep Language Understanding
Cite
@misc{song2020denoising,
title = {{Denoising Diffusion Implicit Models}},
author = {Song, Jiaming and Meng, Chenlin and Ermon, Stefano},
year = {2020},
doi = {10.48550/arxiv.2010.02502},
eprint = {2010.02502},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2010.02502}
}References
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