  The Diffusion model, a prevalent framework for image generation, encounters
significant challenges in terms of broad applicability due to its extended
inference times and substantial memory requirements. Efficient Post-training
Quantization (PTQ) is pivotal for addressing these issues in traditional
models. Different from traditional models, diffusion models heavily depend on
the time-step $t$ to achieve satisfactory multi-round denoising. Usually, $t$
from the finite set $\{1, \ldots, T\}$ is encoded to a temporal feature by a
few modules totally irrespective of the sampling data. However, existing PTQ
methods do not optimize these modules separately. They adopt inappropriate
reconstruction targets and complex calibration methods, resulting in a severe
disturbance of the temporal feature and denoising trajectory, as well as a low
compression efficiency. To solve these, we propose a Temporal Feature
Maintenance Quantization (TFMQ) framework building upon a Temporal Information
Block which is just related to the time-step $t$ and unrelated to the sampling
data. Powered by the pioneering block design, we devise temporal information
aware reconstruction (TIAR) and finite set calibration (FSC) to align the
full-precision temporal features in a limited time. Equipped with the
framework, we can maintain the most temporal information and ensure the
end-to-end generation quality. Extensive experiments on various datasets and
diffusion models prove our state-of-the-art results. Remarkably, our
quantization approach, for the first time, achieves model performance nearly on
par with the full-precision model under 4-bit weight quantization.
Additionally, our method incurs almost no extra computational cost and
accelerates quantization time by $2.0 \times$ on LSUN-Bedrooms $256 \times 256$
compared to previous works. Our code is publicly available at
https://github.com/ModelTC/TFMQ-DM.
