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Which Tokens to Merge? Diffusion Dynamics for Efficient Image Generation
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Proposes DaTMe, a training-free token merging method for diffusion transformers that chooses which tokens to merge using a Tweedie-estimate-based temporal and spatial importance map, evaluated on PixArt-α and FLUX.
Problem
Training-free token merging for accelerating diffusion models often merges structurally important or prompt-unmentioned tokens (e.g., background details) because existing importance signals such as CFG discrepancy are biased toward prompt-aligned foreground, degrading image structure.
Approach
Defines token importance from diffusion dynamics: a temporal signal (inter-step change of the Tweedie clean-image estimate) combined with a spatial signal (high-pass residual of the Tweedie estimate), used to assign anchor (constraint) tokens and merge-source tokens with grid-based source completion and locality-constrained matching.
Key results
- On PixArt-α at compression ratio 0.5, DaTMe reaches CLIP-T 31.01 and FID 43.42 versus CFG-based merging 30.46 / 52.29 and ToMeSD 29.52 / 94.89.
- On PixArt-α at compression ratio 0.3, DaTMe improves SSIM to 0.8112 and LPIPS to 0.1501 versus CFG-based 0.7137 and 0.2369.
- On FLUX.1-dev at compression ratio 0.5, DaTMe reaches SSIM 0.7087 and PSNR 20.20 versus ToMA 0.7009 and 20.04, with higher HPSv2 (28.93 vs 27.76).
Surprising findings
- Replacing the raw score slope with the Tweedie difference as the temporal signal avoids late-step scale-term domination that the authors show makes the score slope unreliable.
Limitations
- Quality degrades under aggressive compression in highly complex scenes with many objects.
- Layer-wise roles of DiT diffusion layers remain underexplored.
- DaTMe is slightly slower in latency than prior methods such as ToMeSD and CFG-based merging on PixArt-α.
Experimental setup
Datasets: COCO 2014 validation set
Benchmarks: COCO 2014 validation (10k prompts)
Metrics: CLIP-T FID HPSv2 SSIM PSNR LPIPS Aesthetic score latency TFLOPs
Baselines: ToMeSD CFG-based merging ToMA PixArt-α (unmerged) FLUX.1-dev (unmerged)
Builds on: ToMeSD CFG-based token merging Token Merging (ToMe) Tweedie's formula
Closest papers by meaning
- Attend to Not Attended: Structure-then-Detail Token Merging for Post-training DiT Acceleration (CVPR 2025 · similarity 0.90)
- ToMA: Token Merge with Attention for Diffusion Models (ICML 2025 · similarity 0.90)
- Multimodal Promptable Token Merging for Diffusion Models (AAAI 2025 · similarity 0.90)
- Diffusion Forcing: Next-token Prediction Meets Full-Sequence Diffusion (NeurIPS 2024 · similarity 0.87)
- Tracing the Roots: Leveraging Temporal Dynamics in Diffusion Trajectories for Origin Attribution (NeurIPS 2025 · similarity 0.87)
- DC-DiT: Adaptive Compute and Elastic Inference for Visual Generation via Dynamic Chunking (NeurIPS 2026 · similarity 0.87)
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