Diffusion models are a class of deep generative models that have shown impressive results on various tasks with dense theoretical founding. Although diffusion models have achieved impressive quality and diversity of sample synthesis than other state-of-the-art models, they still suffer from costly sampling procedure and sub-optimal likelihood estimation. Recent studies have shown great enthusiasm on improving the performance of diffusion model. In this article, we present a first comprehensive review of existing variants of the diffusion models. Specifically, we provide a first taxonomy of diffusion models and categorize them variants to three types, namely sampling-acceleration enhancement, likelihood-maximization enhancement and data-generalization enhancement. We also introduce in detail other five generative models (i.e., variational autoencoders, generative adversarial networks, normalizing flow, autoregressive models, and energy-based models), and clarify the connections between diffusion models and these generative models. Then we make a thorough investigation into the applications of diffusion models, including computer vision, natural language processing, waveform signal processing, multi-modal modeling, molecular graph generation, time series modeling, and adversarial purification. Furthermore, we propose new perspectives pertaining to the development of this generative model.

本文概述了“扩散模型”在图像合成、视频生成、分子设计等领域中的应用, 并将相关研究分为三大类:高效采样、改进似然估计和处理具有特殊结构的数据。此外，还探讨了将扩散模型与其他生成模型相结合以获得更好结果的潜能，在计算机视觉、自然语言生成、时态数据模型等领域具有广泛的应用。本文旨在提供一个全面的扩散模型综述，指出其重点研究领域并指向未来的研究方向。

扩散模型：方法和应用综述