Despite extensive progress on image generation, deep generative models are
suboptimal when applied to lossless compression. For example, models such as
VAEs suffer from a compression cost overhead due to their latent variables that
can only be partially eliminated with elaborated schemes such as bits-back
coding, resulting in oftentimes poor single-sample compression rates. To
overcome such problems, we establish a new class of tractable lossless
compression models that permit efficient encoding and decoding: Probabilistic
Circuits (PCs). These are a class of neural networks involving $|p|$
computational units that support efficient marginalization over arbitrary
subsets of the $D$ feature dimensions, enabling efficient arithmetic coding. We
derive efficient encoding and decoding schemes that both have time complexity
$\mathcal{O} (\log(D) \cdot |p|)$, where a naive scheme would have linear costs
in $D$ and $|p|$, making the approach highly scalable. Empirically, our
PC-based (de)compression algorithm runs 5-20x faster than neural compression
algorithms that achieve similar bitrates. By scaling up the traditional PC
structure learning pipeline, we achieved state-of-the-art results on image
datasets such as MNIST. Furthermore, PCs can be naturally integrated with
existing neural compression algorithms to improve the performance of these base
models on natural image datasets. Our results highlight the potential impact
that non-standard learning architectures may have on neural data compression.