  Diffusion models have demonstrated excellent potential for generating diverse
images. However, their performance often suffers from slow generation due to
iterative denoising. Knowledge distillation has been recently proposed as a
remedy that can reduce the number of inference steps to one or a few without
significant quality degradation. However, existing distillation methods either
require significant amounts of offline computation for generating synthetic
training data from the teacher model or need to perform expensive online
learning with the help of real data. In this work, we present a novel technique
called BOOT, that overcomes these limitations with an efficient data-free
distillation algorithm. The core idea is to learn a time-conditioned model that
predicts the output of a pre-trained diffusion model teacher given any time
step. Such a model can be efficiently trained based on bootstrapping from two
consecutive sampled steps. Furthermore, our method can be easily adapted to
large-scale text-to-image diffusion models, which are challenging for
conventional methods given the fact that the training sets are often large and
difficult to access. We demonstrate the effectiveness of our approach on
several benchmark datasets in the DDIM setting, achieving comparable generation
quality while being orders of magnitude faster than the diffusion teacher. The
text-to-image results show that the proposed approach is able to handle highly
complex distributions, shedding light on more efficient generative modeling.
