  Diffusion models have attained impressive visual quality for image synthesis.
However, how to interpret and manipulate the latent space of diffusion models
has not been extensively explored. Prior work diffusion autoencoders encode the
semantic representations into a semantic latent code, which fails to reflect
the rich information of details and the intrinsic feature hierarchy. To
mitigate those limitations, we propose Hierarchical Diffusion Autoencoders
(HDAE) that exploit the fine-grained-to-abstract and lowlevel-to-high-level
feature hierarchy for the latent space of diffusion models. The hierarchical
latent space of HDAE inherently encodes different abstract levels of semantics
and provides more comprehensive semantic representations. In addition, we
propose a truncated-feature-based approach for disentangled image manipulation.
We demonstrate the effectiveness of our proposed approach with extensive
experiments and applications on image reconstruction, style mixing,
controllable interpolation, detail-preserving and disentangled image
manipulation, and multi-modal semantic image synthesis.
