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Diffusion-4K: Ultra-High-Resolution Image Synthesis with Latent Diffusion Models
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Introduces Diffusion-4K, which builds the Aesthetic-4K benchmark (12,015-image 4K training set, 2,781-image eval set) with GLCM Score and Compression Ratio metrics, and fine-tunes SD3-2B and Flux-12B for direct 4096x4096 synthesis via a partitioned VAE and wavelet-based latent fine-tuning (WLF).
Problem
Direct ultra-high-resolution (4K) text-to-image synthesis with latent diffusion models is largely unexplored, and no public 4K training/evaluation benchmark exists; standard metrics (FID, Aesthetics, CLIPScore) are holistic and low-resolution, poorly capturing fine details.
Approach
Combines a partitioned VAE (F=16 via dilated first conv and partitioned decoder output, avoiding retraining) that fits 4K training in memory with a wavelet (Haar DWT) loss on the velocity-prediction objective that emphasizes high-frequency latent components, plus a 4K benchmark with texture-oriented metrics (GLCM Score, JPEG Compression Ratio).
Key results
- WLF on Flux-F16 at 2048 improves FID from 50.57 to 39.49 and CLIPScore from 30.41 to 34.41 on Aesthetic-Eval@2048.
- On Aesthetic-Eval@4096, SD3-F16-WLF improves GLCM Score from 0.73 to 0.77 and reduces Compression Ratio from 11.97 to 10.50 versus the non-finetuned SD3-F16 baseline.
- Partitioned VAEs with F=16 reconstruct 4096x4096 images with PSNR about 28.8 (SD3-VAE) and 29.2 (Flux-VAE) without retraining, and enable inference that OOMs for F=8.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use GPT-4o captions instead of LAION-5B captions (ablation) | SD3-F16@4096 · Aesthetic-Eval@4096 | CLIPScore: 29.37 -> 33.12 | Helped |
| Use GPT-4o captions instead of LAION-5B captions (ablation) | SD3-F16@4096 · Aesthetic-Eval@4096 | Aesthetics: 5.90 -> 5.97 | Helped |
| Use GPT-4o captions instead of LAION-5B captions (ablation) | Flux-F16@4096 · Aesthetic-Eval@4096 | CLIPScore: 29.12 -> 33.67 | Helped |
| Use GPT-4o captions instead of LAION-5B captions (ablation) | Flux-F16@4096 · Aesthetic-Eval@4096 | Aesthetics: 6.02 -> 6.11 | Helped |
| Add WLF fine-tuning instead of fine-tuning without WLF (ablation) | SD3-F16@4096 · Aesthetic-Eval@4096 | CLIPScore: 34.14 -> 34.40 | Helped |
| Add WLF fine-tuning instead of fine-tuning without WLF (ablation) | SD3-F16@4096 · Aesthetic-Eval@4096 | Aesthetics: 5.99 -> 6.07 | Helped |
| Add WLF fine-tuning instead of fine-tuning without WLF (ablation) | SD3-F16@4096 · Aesthetic-Eval@4096 | GLCM Score: 0.74 -> 0.77 | Helped |
| Add WLF fine-tuning instead of fine-tuning without WLF (ablation) | SD3-F16@4096 · Aesthetic-Eval@4096 | Compression Ratio: 11.41 -> 10.50 | Helped |
Surprising findings
- Using GPT-4o-generated captions instead of LAION-5B original captions raises CLIPScore by roughly 4-5 points at 4096 resolution.
Limitations
- Evaluation relies on the authors' own metrics (GLCM Score, Compression Ratio) with limited correlation to human judgment (SRCC about 0.36-0.75).
- Gains from WLF over plain fine-tuning are modest (e.g., GLCM 0.74 to 0.77; CLIPScore 34.14 to 34.40).
- Training was on a curated internet image set; the 4K training data is not stated as released.
Experimental setup
Datasets: Aesthetic-Train (12,015 images, GPT-4o captions) LAION-Aesthetics V2 6.5+ (evaluation source)
Benchmarks: Aesthetic-Eval@2048 Aesthetic-Eval@4096
Metrics: FID CLIPScore Aesthetics GLCM Score Compression Ratio rFID PSNR SSIM LPIPS
Baselines: PixArt-Σ Sana Stable Cascade SD3-F8 (original VAE) Flux-F8 (original VAE)
Builds on: Stable Diffusion 3 Flux rectified flow PixArt-Σ
Closest papers by meaning
- SDXL: Improving Latent Diffusion Models for High-Resolution Image Synthesis (ICLR 2024 · similarity 0.90)
- DiffuseHigh: Training-Free Progressive High-Resolution Image Synthesis Through Structure Guidance (AAAI 2025 · similarity 0.89)
- UltraHR-100K: Enhancing UHR Image Synthesis with A Large-Scale High-Quality Dataset (NeurIPS 2025 · similarity 0.89)
- Simpler Diffusion: 1.5 FID on ImageNet512 with Pixel-space Diffusion (CVPR 2025 · similarity 0.89)
- Any-Size-Diffusion: Toward Efficient Text-Driven Synthesis for Any-Size HD Images (AAAI 2024 · similarity 0.89)
- UltraDiff:Transferring High-Fidelity Priors to Compressed Latent Spaces for High-resolution Image Generation (NeurIPS 2026 · similarity 0.88)
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