Ricardo (2023-06-30 23:49):
#paper Denoising Diffusion Probabilistic Models. doi: https://doi.org/10.48550/arXiv.2006.11239 大名鼎鼎的DDPM模型,算法结构出奇的简单,分为前向加噪过程和反向去噪过程。前向加噪过程是通过在多个时间步里加小噪声,反向去噪过程则在每一个时间步上通过网络学习噪声分布去掉噪声。通过一长串的公式推导,其最终的损失函数相当的简单,就是个mse。看起来就像是很多个VAE叠加在一起。DDPM的一个缺点就是采样步长很长,通常需要1000步以上;而之后提出的DDIM模型将这个采样步长缩小到了50步左右,而这个效果是通过牺牲生成样本多样性实现的。DDIM模型通过一个叫做飘逸扩散方程的模型(这个模型在行为决策等研究中常常被采纳)来解释其原理。原本的DDPM模型其实只有漂移扩散方程中的扩散部分,而DDIM模型则加上了漂移的部分,可以将模型往数据采样密度较高的地方去靠近。
Denoising Diffusion Probabilistic Models
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Abstract:
We present high quality image synthesis results using diffusion probabilistic models, a class of latent variable models inspired by considerations from nonequilibrium thermodynamics. Our best results are obtained by training on a weighted variational bound designed according to a novel connection between diffusion probabilistic models and denoising score matching with Langevin dynamics, and our models naturally admit a progressive lossy decompression scheme that can be interpreted as a generalization of autoregressive decoding. On the unconditional CIFAR10 dataset, we obtain an Inception score of 9.46 and a state-of-the-art FID score of 3.17. On 256x256 LSUN, we obtain sample quality similar to ProgressiveGAN. Our implementation is available at this https URL
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