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JetFormer: An autoregressive generative model of raw images and text
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Proposes JetFormer, a decoder-only transformer trained end-to-end from raw pixels and text, using a normalizing flow to produce soft-token image representations that feed a GMM-headed autoregressive model.
Problem
Joint generative modeling of images and text typically relies on separately pretrained, frozen, lossy image tokenizers (VQ-VAE/VAE), which limits end-to-end optimization and likelihood-based training on raw pixels.
Approach
Use an invertible normalizing flow as a trainable image encoder/decoder producing soft tokens, trained jointly with an autoregressive transformer via a GMM loss on image soft tokens and cross-entropy on text, with an RGB Gaussian-noise curriculum and factored-out redundant dimensions to guide learning toward high-level structure.
Key results
- JetFormer-L achieves FID 6.64 on ImageNet256 class-conditional generation (500 epochs) without any pretrained component, competitive with GIVT-Causal (3.35) and LDM-4-G (3.60).
- JetFormer-L (T2I) reaches zero-shot COCO FID-30k of 18.63 at 2.75B parameters, versus 12.08 for MAGVLT (T&I) and 10.39 for DALL-E-2.
- JetFormer-L (T&I) reaches COCO captioning CIDEr 119.8 and VQAv2 accuracy 70.0 after fine-tuning, exceeding CapPa and CLIP L/14 at the 900M-pair setting.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| add the normalizing flow (ablation) | JetFormer-B · ImageNet256, 100 epochs | FID: 117.76 -> 7.84 | Helped |
| add the noise curriculum (ablation) | JetFormer-B · ImageNet256, 100 epochs | FID: 44.71 -> 7.84 | Helped |
| factor out latent dimensions after the flow (ablation) | JetFormer-B · ImageNet256, 100 epochs | FID: 17.29 -> 7.84 | Helped |
| train the flow and transformer end-to-end (ablation) | JetFormer-B · ImageNet256, 100 epochs | FID: 11.16 -> 7.84 | Helped |
| factor out dimensions after the flow rather than with a learned projection before it (ablation) | JetFormer-B · ImageNet256, 100 epochs | FID: 10.19 -> 7.84 | Helped |
| use a GMM instead of a single Gaussian for the soft-token loss (ablation) | JetFormer-B · ImageNet256, 100 epochs | Recall: 0.30 -> 0.39 | Helped |
| use 16 class tokens instead of one (ablation) | JetFormer-B · ImageNet256, 100 epochs | FID: 8.85 -> 7.84 | Helped |
| use a noise curriculum with PCA preprocessing (ablation) | JetFormer-B with PCA preprocessing · ImageNet256, 100 epochs | FID: 13.16 -> 8.79 | Helped |
| set initial noise standard deviation to 64 rather than 128 (ablation) | JetFormer-B · ImageNet256 | FID: 8.62 -> 7.84 | Helped |
| apply a noise curriculum rather than no curriculum (ablation) | JetFormer-B · ImageNet256, 100 epochs | NLL: 3.05 -> 3.14 | Hurt |
| add a noise curriculum to the two-stage VAE + Transformer baseline (ablation) | VAE + Transformer (2 stages) · COCO-FID30k | FID: 95.4 -> 87.6 | Helped |
| train the model end-to-end with a normalizing flow rather than use a two-stage VAE representation (ablation) | JetFormer-B T&I · COCO-FID30k | FID: 95.4 -> 30.6 | Helped |
Surprising findings
- Removing the noise curriculum raises ImageNet FID from 7.84 to 44.71 while NLL barely changes (3.14 vs 3.05), showing NLL alone does not track sample quality.
- A PCA-preprocessed variant gets similar FID with the noise curriculum less important, yet end-to-end JetFormer still performs better in ablations.
Limitations
- Sample visual quality lags behind state-of-the-art diffusion models that use pretrained latent representations.
- Full end-to-end training increases computational requirements.
- Text-to-image quality is worse than VQ-VAE-based models like MAGVLT, while the T&I variant trades off T2I quality for understanding.
Experimental setup
Datasets: ImageNet1k WebLI C4 (tokenizer) MS-COCO VQAv2
Benchmarks: ImageNet256 class-conditional generation (ADM FID-50k) MS-COCO FID-30k zero-shot and fine-tuned ImageNet zero-shot classification COCO captioning CIDEr VQAv2 test-dev
Metrics: FID precision recall NLL (bits per dimension) CIDEr VQAv2 accuracy zero-shot ImageNet accuracy
Baselines: BigGAN-deep ADM-G LDM-4-G VQGAN ViT-VQGAN GIVT-Causal DALL-E CogView CogView2 MAGVLT ARGVLT Make-A-Scene
Builds on: GIVT Gemma normalizing flow coupling layers (Glow-style) VQGAN classifier-free guidance
Closest papers by meaning
- STARFlow2: Bridging Language Models and Normalizing Flows for Unified Multimodal Generation (NeurIPS 2026 · similarity 0.89)
- JanusFlow: Harmonizing Autoregression and Rectified Flow for Unified Multimodal Understanding and Generation (CVPR 2025 · similarity 0.89)
- LMFusion: Adapting Pretrained Language Models for Multimodal Generation (NeurIPS 2025 · similarity 0.88)
- Leveraging Unpaired Data for Vision-Language Generative Models via Cycle Consistency (ICLR 2024 · similarity 0.88)
- Dual Diffusion for Unified Image Generation and Understanding (CVPR 2025 · similarity 0.88)
- A Spark of Vision-Language Intelligence: 2-Dimensional Autoregressive Transformer for Efficient Finegrained Image Generation (ICLR 2025 · similarity 0.88)
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