Look-Ahead and Look-Back Flows: Training-Free Image Generation with Trajectory Smoothing
Abstract
Recent advances have reformulated diffusion models as deterministic ordinary differential equations (ODEs) through the framework of flow matching, providing a unified formulation for the noise-to-data generative process. Various training-free flow matching approaches have been developed to improve image generation through flow velocity field adjustment, eliminating the need for costly retraining. However, Modifying the velocity field v introduces errors that propagate through the full generation path, whereas adjustments to the latent trajectory z are naturally corrected by the pretrained velocity network, reducing error accumulation. In this paper, we propose two complementary training-free latent-trajectory adjustment approaches based on future and past velocity v and latent trajectory z information that refine the generative path directly in latent space. We propose two training-free trajectory smoothing schemes: Look-Ahead, which averages the current and next-step latents using a curvature-gated weight, and Look-Back, which smoothes latents using an exponential moving average with decay. We demonstrate through extensive experiments and comprehensive evaluation metrics that the proposed training-free trajectory smoothing models substantially outperform various state-of-the-art models across multiple datasets including COCO17, CUB-200, and Flickr30K.