How do you perform hyperparameter tuning specifically for diffusion models?

Hyperparameter tuning for diffusion models focuses on optimizing parameters that control the training process, noise scheduling, and sampling efficiency. Key hyperparameters include the number of diffusion timesteps (T), the noise schedule (how noise is added across timesteps), learning rate, batch size, and architectural choices like network depth. For example, the number of timesteps directly impacts both training stability and sample quality: too few steps may lead to underfitting, while too many can slow training without meaningful gains. The noise schedule—often linear, cosine, or custom—determines how quickly noise is added and removed, affecting the model’s ability to learn gradual data transformations. Learning rate and optimizer settings (e.g., Adam’s beta values) also require careful tuning to avoid divergence or slow convergence.

A practical approach involves starting with established baselines (e.g., T=1000 steps and a linear noise schedule) and iteratively adjusting parameters based on validation metrics. For instance, reducing T to 500 steps while switching to a cosine schedule might improve sample quality with fewer computations. Batch size should balance memory constraints and model performance—larger batches often stabilize training but require more GPU memory. Tools like grid search or Bayesian optimization can automate the exploration of hyperparameter combinations. For example, testing learning rates in [1e-4, 3e-4] with batch sizes [32, 64] while monitoring metrics like Fréchet Inception Distance (FID) helps identify optimal configurations. Additionally, tuning the loss function’s weighting (e.g., focusing on specific timesteps) can address imbalances in how the model learns different noise levels.

Sampling-specific hyperparameters, such as the number of denoising steps during inference, also require tuning. Techniques like DDIM (Denoising Diffusion Implicit Models) allow fewer sampling steps than training steps, but the step count and noise removal thresholds must be adjusted to avoid artifacts. For conditional models, parameters like classifier-free guidance scales (e.g., setting a scale of 7.5 for text-to-image models) significantly influence output alignment with inputs. Tools like Weights & Biases or TensorBoard can track experiments, visualizing how changes in parameters like noise schedule or guidance scale affect outputs. For example, a developer might discover that a guidance scale of 5.0 produces more detailed images without over-saturating colors. By systematically testing these parameters and prioritizing metrics tied to the use case (e.g., FID for fidelity, inference speed for real-time applications), developers can optimize diffusion models effectively.