Stability and Generalizability in SDE Diffusion Models with Measure-Preserving Dynamics

Inverse problems describe the process of estimating the causal factors from a set of measurements or data. Mapping of often incomplete or degraded data to parameters is ill-posed, thus data-driven iterative solutions are required, for example when reconstructing clean images from poor signals. Diffusion models have shown promise as potent generative tools for solving inverse problems due to their superior reconstruction quality and their compatibility with iterative solvers. However, most existing approaches are limited to linear inverse problems represented as Stochastic Differential Equations (SDEs). This simplification falls short of addressing the challenging nature of real-world problems, leading to amplified cumulative errors and biases. We provide an explanation for this gap through the lens of measure-preserving dynamics of Random Dynamical Systems (RDS) with which we analyse Temporal Distribution Discrepancy and thus introduce a theoretical framework based on RDS for SDE diffusion models. We uncover several strategies that inherently enhance the stability and generalizability of diffusion models for inverse problems and introduce a novel score-based diffusion framework, the \textbf{D}ynamics-aware S\textbf{D}E \textbf{D}iffusion \textbf{G}enerative \textbf{M}odel (D$^3$GM). The \textit{Measure-preserving property} can return the degraded measurement to the original state despite complex degradation with the RDS concept of \textit{stability}. Our extensive experimental results corroborate the effectiveness of D$^3$GM across multiple benchmarks including a prominent application for inverse problems, magnetic resonance imaging. Code and data will be publicly available.

Paper

Similar papers

Peer review

Reviewer z6fz7/10 · confidence 4/52024-06-26

Summary

The author(s) of the paper provides a theoretically sound method of a Dynamics-aware SDE Diffusion Generative Model (D^3GM) to enhance the stability and generalizability of inverse problem diffusion models. The authors provide a rigorous mathematical examination of the temporal distribution discrepancy for the instability issue of transitionary score-based generative models. The analysis extends the traditional Ornstein-Uhlenbeck (OU) process to random dynamical systems (RDS), focusing on the stability of SDE. The authors then proposed a novel method (D^3GM) that combines the stationary process to relieve the temporal distribution discrepancy problem following the measure-preserving dynamics from RDS; this method could guide the SDE diffusion to a desired stable solution. The experimental results from the authors also indicate the efficiency of D^3GM under different situations.

Strengths

1. The authors provide a novel method (D^3GM) integrating measure-preserving dynamics into SDE diffusion models. This is the fundamental contribution of this paper. 2. Extending the Ornstein-Uhlenbeck process to a random dynamical system is innovative, allowing the community to better understand the instability problems of diffusion models. This paper also provides a detailed mathematical measurement of the discrepancy between the reference and the retrieved data. 3. The logic of this paper is clear.

Weaknesses

1. The paper is theoretically sound, but it might be difficult for readers with no math background to follow. Consider adding more explanations for the theoretical part. 2. See below

Questions

1. Although this paper has solid theoretical support, the experiment is not as good as the theoretical part. It would be helpful if the authors could add more visual comparisons between these models (I noticed Figure 3, but from the set of results, there seems to be no significant improvement). This would help readers get a clear understanding of the proposed method's exact performance compared with other methods. 2. at line 217, the COS is chosen to balance 'the trade-off between complexity and effectiveness'. This is unclear; it will be helpful to add more theoretical support or a set of experiments to empirically show COS is better than other options.

Rating

7

Confidence

4

Soundness

4

Presentation

3

Contribution

3

Limitations

Even though the paper fulfills the theoretical gap, the actual improvement of the model performance seems limited.

Reviewer J29t5/10 · confidence 3/52024-07-12

Summary

The paper addresses the use of diffusion models in solving inverse problems, which involve estimating causal factors from degraded data. Traditional methods often fall short in real-world scenarios due to accumulated errors and biases. To tackle these issues, the authors propose a new theoretical framework based on measure-preserving dynamics of Random Dynamical Systems (RDS) for Stochastic Differential Equation (SDE) diffusion models. They introduce the Dynamics-aware SDE Diffusion Generative Model (D3GM), which enhances the stability and generalizability of these models. Experimental results, particularly in magnetic resonance imaging (MRI), demonstrate the framework’s effectiveness.

Strengths

Solving inverse problems is critical in many real-world applications. Discussing the problem from the measure-preserving dynamical system perspective is interesting.

Weaknesses

1. It is unclear to me how this work is different from DDBM [1] and Augmented bridge matching [2]. In fact, DDBM's setting is more general by considering diffusion bridges derived from h-transform. That setting covers OU processes (with some reparameterization on t if necessary). 2. The empirical study does not include an evaluation on the sampled image quality. (It is mentioned at L245 that FID will be reported; however, I did not find any in the paper. ) 3. The connection between the theoretical work in Sec 3 and the implementation in Sec 4 is unclear. 4. There are multiple choices of drift and diffusion coefficients. However, there are no discussions/ablation studies to show how to choose them. 5. There is no performance comparison with similar implementations like DDBM and I2SB. [1] Denoising Diffusion Bridge Models, Linqi Zhou, Aaron Lou, Samar Khanna, Stefano Ermon, 2023 [2] Augmented bridge matching, Valentin De Bortoli, Guan-Horng Liu, Tianrong Chen, Evangelos A Theodorou, Weilie Nie, 2023

Questions

I have mentioned several problems in the Weakness section. In addition, 1. For the training of NN, e.g. dehazing, you mentioned there were only 100 pairs images for training and testing. Is the model barely trained with this much data?

Rating

5

Confidence

3

Soundness

3

Presentation

2

Contribution

2

Limitations

I am not aware of any potential negative societal impact of this work.

Reviewer APgH7/10 · confidence 3/52024-07-28

Summary

Given that existing diffusion models are limited to linear inverse problems, this paper proposes to use measure-preserving dynamics of random dynamical systems to formulate a theoretical framework for SDE diffusion models. They uncover several strategies that inherently enhance the stability and generalizability of diffusion models for inverse problems and introduce a score-based diffusion framework, D3GM. The measure-preserving property can return the degraded measurement to the original state despite complex degradation with the RDS concept of stability. Experiments on multiple restoration and reconstruction tasks, such as dehazing, deraining, and MRI reconstruction, demonstrate the stability and generalizability of the proposed D3GM framework.

Strengths

- The theoretical results are interesting and open up many potential paths for future investigations. - Clearly explains the advantages of measure-preserving dynamics in SDE diffusion, and how they motivate algorithmic design. - For some challenging applications, such as MRI super-resolution, the derived model shows excellent generative capabilities and outperforms some well-known baseline methods. - The writing is clear and the paper is well structured.

Weaknesses

- The connection between the measure-preserving property and the proposed D3GM is not well-explained, and how the temporal distribution discrepancy is mitigated within D3GM is not intuitive. - Why choose the perspective of measure-preserving dynamics of random dynamical systems? What unique advantages does it offer in solving challenging inverse problems? Besides the related instability analysis, are there more intuitive explanations available? - The baselines used for comparison in the dehazing and deraining tasks are somewhat outdated, which raises questions about the real-world effectiveness of the proposed methods when compared to state-of-the-art approaches. - Strictly speaking, although the paper provides some theoretical insights, it does not systematically resolve the issues, and the intuitions gained appear somewhat heuristic.

Questions

Please refer to the weaknesses.

Rating

7

Confidence

3

Soundness

3

Presentation

3

Contribution

3

Limitations

Yes

Authorsrebuttal2024-08-12

Dear Reviewers, We would like to kindly remind you that the author-reviewer discussion period will be ending soon (Aug 13 11:59pm AoE). We greatly appreciate your time and effort in reviewing our work and would be delighted to engage in further discussions to address any remaining concerns you may have. Please do not hesitate to contact us if you have any questions or require additional information. Best regards, Authors

Reviewer J29t2024-08-12

I thank the authors for the detailed replies. While the authors have argued that the proposed methods differ greatly from DDBM/I2SB, I still think many overlaps exist between them. In addition, though DDBM was published in 2024, it was uploaded to arxiv in Sep 2023. Regardlessly, considering that the submission made some solid theoretical contributions, I am raising the score to 5.

Program Chairsdecision2024-09-25

Decision

Accept (poster)

© 2026 NYSGPT2525 LLC