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arXiv · 1703.03664

Parallel Multiscale Autoregressive Density Estimation

Scott Reed·Aäron van den Oord·Nal Kalchbrenner·Sergio Gómez Colmenarejo·Ziyu Wang·Dan Belov·Nando de Freitas
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Abstract

PixelCNN achieves state-of-the-art results in density estimation for natural images. Although training is fast, inference is costly, requiring one network evaluation per pixel; O(N) for N pixels. This can be sped up by caching activations, but still involves generating each pixel sequentially. In this work, we propose a parallelized PixelCNN that allows more efficient inference by modeling certain pixel groups as conditionally independent. Our new PixelCNN model achieves competitive density estimation and orders of magnitude speedup - O(log N) sampling instead of O(N) - enabling the practical generation of 512x512 images. We evaluate the model on class-conditional image generation, text-to-image synthesis, and action-conditional video generation, showing that our model achieves the best results among non-pixel-autoregressive density models that allow efficient sampling.

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Scott Reed, Aäron van den Oord, Nal Kalchbrenner, Sergio Gómez Colmenarejo, Ziyu Wang, Dan Belov, Nando de Freitas. 2017-03-10. Parallel Multiscale Autoregressive Density Estimation. https://arxiv.org/abs/1703.03664

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