Diffusion models have demonstrated compelling generation quality by
optimizing the variational lower bound through a simple denoising score
matching loss. In this paper, we provide theoretical evidence that the
prevailing practice of using a constant loss weight strategy in diffusion
models leads to biased estimation during the training phase. Simply optimizing
the denoising network to predict Gaussian noise with constant weighting may
hinder precise estimations of original images. To address the issue, we propose
an elegant and effective weighting strategy grounded in the theoretically
unbiased principle. Moreover, we conduct a comprehensive and systematic
exploration to dissect the inherent bias problem deriving from constant
weighting loss from the perspectives of its existence, impact and reasons.
These analyses are expected to advance our understanding and demystify the
inner workings of diffusion models. Through empirical evaluation, we
demonstrate that our proposed debiased estimation method significantly enhances
sample quality without the reliance on complex techniques, and exhibits
improved efficiency compared to the baseline method both in training and
sampling processes.

通过理论支持，本文提出一种优雅而有效的加权策略，解决了扩散模型中常数加权策略带来的估计偏差问题。并通过实证评估表明，提出的去偏估计方法在样本质量、训练效率和采样效率方面均显著优于基准方法。

去偏扩散模型的训练

Debias the Training of Diffusion Models

Diffusion models learn to restore noisy data, which is corrupted with
different levels of noise, by optimizing the weighted sum of the corresponding
loss terms, i.e., denoising score matching loss. In this paper, we show that
restoring data corrupted with certain noise levels offers a proper pretext task
for the model to learn rich visual concepts. We propose to prioritize such
noise levels over other levels during training, by redesigning the weighting
scheme of the objective function. We show that our simple redesign of the
weighting scheme significantly improves the performance of diffusion models
regardless of the datasets, architectures, and sampling strategies.

本文研究了扩散模型学习以优化对应丢失函数的加权和（去噪得分匹配损失）来恢复不同噪声水平的嘈杂数据，并提出了恢复受特定噪声水平损坏的数据作为学习丰富视觉概念的适当预先任务的方法，通过重新设计目标函数的加权方案，在训练过程中优先考虑这些噪声水平，我们证明了我们简单的加权方案重构可以显著提高扩散模型的性能。