Variational autoencoders (VAEs) are one of the powerful likelihood-based generative models with applications in various domains. However, they struggle to generate high-quality images, especially when samples are obtained from the prior without any tempering. One explanation for VAEs' poor generative quality is the prior hole problem: the prior distribution fails to match the aggregate approximate posterior. Due to this mismatch, there exist areas in the latent space with high density under the prior that do not correspond to any encoded image. Samples from those areas are decoded to corrupted images. To tackle this issue, we propose an energy-based prior defined by the product of a base prior distribution and a reweighting factor, designed to bring the base closer to the aggregate posterior. We train the reweighting factor by noise contrastive estimation, and we generalize it to hierarchical VAEs with many latent variable groups. Our experiments confirm that the proposed noise contrastive priors improve the generative performance of state-of-the-art VAEs by a large margin on the MNIST, CIFAR-10, CelebA 64, and CelebA HQ 256 datasets.

针对变分自编码器的先验洞问题，我们提出了一种能源化先验，通过基础先验分布和重新加权因子的乘积来定义，以使基础先验更接近集体后验，并通过噪声对比估计来训练重新加权因子，实验证明此方法可以大幅提高MNIST、CIFAR-10、CelebA 64和CelebA HQ 256数据集上的最先进VAE的生成性能。

用对比学习的方法训练变分自编码器先验