Warm Starts Accelerate Conditional Diffusion
This addresses the efficiency problem for users of generative models, offering a simple and synergistic acceleration method that is incremental but impactful.
The paper tackles the slow sampling speed of conditional diffusion models by introducing Warm-Start Diffusion (WSD), which uses a deterministic model to provide an informed prior, reducing the number of function evaluations needed to 4-6 for realistic samples and saturating performance with 10-12.
Generative models like diffusion and flow-matching create high-fidelity samples by progressively refining noise. The refinement process is notoriously slow, often requiring hundreds of function evaluations. We introduce Warm-Start Diffusion (WSD), a method that uses a simple, deterministic model to dramatically accelerate conditional generation by providing a better starting point. Instead of starting generation from an uninformed $N(\boldsymbol{0}, I)$ prior, our deterministic warm-start model predicts an informed prior $N(\hat{\boldsymbolμ}_C, \text{diag}(\hat{\boldsymbolσ}^2_C))$, whose moments are conditioned on the input context $C$. This warm start substantially reduces the distance the generative process must traverse, and therefore the number of diffusion steps required, particularly when the context $C$ is strongly informative. WSD is applicable to any standard diffusion or flow matching algorithm, is orthogonal to and synergistic with other fast sampling techniques like efficient solvers, and is simple to implement. We test WSD in a variety of settings, and find that it substantially outperforms standard diffusion in the efficient sampling regime, generating realistic samples using only 4-6 function evaluations, and saturating performance with 10-12.