NVAE: A Deep Hierarchical Variational Autoencoder (Paper Explained)

VAEs have been traditionally hard to train at high resolutions and unstable when going deep with many layers. In addition, VAE samples are often more blurry and less crisp than those from GANs. This paper details all the engineering choices necessary to successfully train a deep hierarchical VAE that exhibits global consistency and astounding sharpness at high resolutions.

OUTLINE: 0:00 - Intro & Overview 1:55 - Variational Autoencoders 8:25 - Hierarchical VAE Decoder 12:45 - Output Samples 15:00 - Hierarchical VAE Encoder 17:20 - Engineering Decisions 22:10 - KL from Deltas 26:40 - Experimental Results 28:40 - Appendix 33:00 - Conclusion

Paper: https://arxiv.org/abs/2007.03898

Abstract: Normalizing flows, autoregressive models, variational autoencoders (VAEs), and deep energy-based models are among competing likelihood-based frameworks for deep generative learning. Among them, VAEs have the advantage of fast and tractable sampling and easy-to-access encoding networks. However, they are currently outperformed by other models such as normalizing flows and autoregressive models. While the majority of the research in VAEs is focused on the statistical challenges, we explore the orthogonal direction of carefully designing neural architectures for hierarchical VAEs. We propose Nouveau VAE (NVAE), a deep hierarchical VAE built for image generation using depth-wise separable convolutions and batch normalization. NVAE is equipped with a residual parameterization of Normal distributions and its training is stabilized by spectral regularization. We show that NVAE achieves state-of-the-art results among non-autoregressive likelihood-based models on the MNIST, CIFAR-10, and CelebA HQ datasets and it provides a strong baseline on FFHQ. For example, on CIFAR-10, NVAE pushes the state-of-the-art from 2.98 to 2.91 bits per dimension, and it produces high-quality images on CelebA HQ as shown in Fig. 1. To the best of our knowledge, NVAE is the first successful VAE applied to natural images as large as 256×256 pixels.

Authors: Arash Vahdat, Jan Kautz

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