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FouRA: Fourier Low-Rank Adaptation
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Proposes FouRA, a LoRA variant that applies low-rank projections in the Fourier/DCT domain with an input-dependent learned rank-gating mask, improving diversity and quality of LoRA-finetuned text-to-image diffusion models and enabling training-free adapter merging.
Problem
LoRA-finetuned text-to-image diffusion models suffer from low diversity (data copying / distribution collapse), worsened by high adapter strength, high rank, and small training sets; merging multiple LoRAs is also prone to artifacts.
Approach
Apply the low-rank down/up projections in the frequency domain (1D DFT or DCT along the embedding dimension) with a learnable, input- and timestep-dependent gating over the rank-r singular components, folding the adapter strength alpha into the low-rank subspace.
Key results
- On Paintings with Realistic Vision-v3.0 at alpha=1.0, FouRA reaches LPIPS diversity 44.2 and HPSv2 28.4 vs LoRA 38.3 and 24.6 (rank 64, 30 seeds).
- Merging BlueFire and Paintings adapters at alpha 1.0, FouRA HPSv2 is 33.1 vs LoRA 30.3, with FouRA ahead at every tested strength.
- On GLUE with RoBERTa-Base, FouRA outperforms SoRA on four of six tasks (e.g., CoLA 70.6 vs 69.9, QNLI 94.2 vs 93.9).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use FouRA instead of LoRA | Stable Diffusion-v1.5 on Paintings · Paintings (α=1) | LPIPS Diversity: 38.3 ± 3.6 -> 43.9 ± 3.7 | Helped |
| Use FouRA instead of LoRA | Stable Diffusion-v1.5 on Paintings · Paintings (α=1) | HPSv2: 22.3 ± 1.7 -> 25.2 ± 1.6 | Helped |
| Use FouRA instead of LoRA | Realistic Vision-v3.0 on Paintings · Paintings (α=1) | LPIPS Diversity: 38.3 ± 3.5 -> 44.2 ± 3.7 | Helped |
| Use FouRA instead of LoRA | Realistic Vision-v3.0 on Paintings · Paintings (α=1) | HPSv2: 24.6 ± 1.8 -> 28.4 ± 1.8 | Helped |
| Use FouRA instead of LoRA | Stable Diffusion-v1.5 on Blue-Fire · Blue-Fire (α=1) | LPIPS Diversity: 47.8 ± 3.7 -> 50.3 ± 3.0 | Helped |
| Use FouRA instead of LoRA | Stable Diffusion-v1.5 on Blue-Fire · Blue-Fire (α=1) | HPSv2: 28.6 ± 2.1 -> 29.7 ± 1.9 | Helped |
| Use FouRA instead of LoRA | Realistic Vision-v3.0 on Blue-Fire · Blue-Fire (α=1) | LPIPS Diversity: 46.8 ± 4.0 -> 50.4 ± 3.0 | Helped |
| Use FouRA instead of LoRA | Realistic Vision-v3.0 on Blue-Fire · Blue-Fire (α=1) | HPSv2: 32.7 ± 1.6 -> 33.6 ± 1.5 | Helped |
| Use FouRA instead of LoRA | RoBERTa-Base · CoLA | MCC: 67.3 ± 0.8 -> 70.6 ± 0.7 | Helped |
| Use FouRA instead of LoRA | RoBERTa-Base · SST2 | accuracy: 94.9 ± 0.3 -> 95.5 ± 0.4 | Helped |
| Use FouRA instead of LoRA | RoBERTa-Base · STSB | correlation: 89.9 ± 0.3 -> 91.6 ± 0.1 | Helped |
| Use FouRA instead of LoRA | RoBERTa-Base · MRPC | score: 90.3 ± 0.6 -> 90.4± 0.5 | No clear effect |
Surprising findings
- FouRA's HPSv2 remains above the best LoRA score across all ranks, suggesting the frequency-domain gating reduces the rank sensitivity of LoRA.
Limitations
- Experiments on small style datasets (30-90 images) and a limited set of styles and concepts.
- Evaluation relies on learned metrics (HPSv2.1, LPIPS diversity) rather than human studies.
Experimental setup
Datasets: BlueFire Paintings Origami 3D GLUE concept slider attribute prompts
Benchmarks: GLUE BlueFire validation Paintings validation
Metrics: LPIPS diversity HPSv2.1 LPIPS similarity accuracy Matthews correlation Pearson/Spearman correlation
Baselines: LoRA SoRA AdaLoRA
Builds on: LoRA SoRA concept sliders soft gating
Closest papers by meaning
- GraLoRA: Granular Low-Rank Adaptation for Parameter-Efficient Fine-Tuning (NeurIPS 2025 · similarity 0.88)
- Flat-LoRA: Low-Rank Adaptation over a Flat Loss Landscape (ICML 2025 · similarity 0.88)
- LoRAtorio: An intrinsic approach to LoRA Skill Composition (NeurIPS 2026 · similarity 0.88)
- RandLoRA: Full rank parameter-efficient fine-tuning of large models (ICLR 2025 · similarity 0.88)
- Decoupling Angles and Strength in Low-rank Adaptation (ICLR 2025 · similarity 0.88)
- Parameter-Efficient Fine-Tuning with Discrete Fourier Transform (ICML 2024 · similarity 0.88)
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