Introduction

This work challenges the residual prediction paradigm in visual autoregressive modeling and presents FlexVAR, a new Flexible Visual AutoRegressive image generation paradigm. FlexVAR facilitates autoregressive learning with ground-truth prediction, enabling each step to independently produce plausible images. This simple, intuitive approach swiftly learns visual distributions and makes the generation process more flexible and adaptable. Trained solely on low-resolution images ($\leq$ 256px), FlexVAR can: (1) Generate images of various resolutions and aspect ratios, even exceeding the resolution of the training images. (2) Support various image-to-image tasks, including image refinement, in/out-painting, and image expansion. (3) Adapt to various autoregressive steps, allowing for faster inference with fewer steps or enhancing image quality with more steps. Our 1.0B model outperforms its VAR counterpart on the ImageNet 256x256 benchmark. Moreover, when zero-shot transfer the image generation process with 13 steps, the performance further improves to 2.08 FID, outperforming state-of-the-art autoregressive models AiM/VAR by 0.25/0.28 FID and popular diffusion models LDM/DiT by 1.52/0.19 FID, respectively. When transferring our 1.0B model to the ImageNet 512x512 benchmark in a zero-shot manner, FlexVAR achieves competitive results compared to the VAR 2.3B model, which is a fully supervised model trained at 512x512 resolution.

Installation

1. Install torch>=2.0.0.

2. Install other pip packages via pip3 install -r requirements.txt.

3. Prepare the ImageNet dataset

   assume the ImageNet is in `/path/to/imagenet`. It should be like this:

   /path/to/imagenet/:
       train/:
           n01440764: 
               many_images.JPEG ...
           n01443537:
               many_images.JPEG ...
       val/:
           n01440764:
               ILSVRC2012_val_00000293.JPEG ...
           n01443537:
               ILSVRC2012_val_00000236.JPEG ...
   

   NOTE: The arg --data_path=/path/to/imagenet should be passed to the training script.

4. (Optional) install and compile flash-attn and xformers for faster attention computation.

VAR zoo

• VQVAE Tokenizer

  You need to download FlexVAE.pth first.

• FlexVAR-Transformer

  	FID	IS	Step	Weights
  d16	3.05	291.3	10	FlexVARd16-epo179.pth
  d20	2.41	299.3	10	FlexVARd20-epo249.pth
  d24	2.21	299.1	10	FlexVARd16-epo349.pth

Evaluation

• 256x256 (default)

  For FID evaluation, use var.autoregressive_infer_cfg to sample 50,000 images (50 per class) and save them as PNG (not JPEG) files in a folder. Pack them into a .npz file. Then use the OpenAI's FID evaluation toolkit and reference ground truth npz file of 256x256 to evaluate FID, IS, precision, and recall. See Evaluation for details

  For example, evaluate our pre-trained FlexVARd20-epo249.pth model:

  # 1. Download FlexVARd24-epo349.pth.
  # 2. put it at `pretrained/FlexVARd20-epo349.pth`.
  # 3. evaluation
    args_infer_patch_nums="1_2_3_4_5_7_10_13_16"
    torchrun --nnodes=1 --nproc_per_node=2 --node_rank=0  eval_c2i.py  --batch_size 16  --cfg 2.5 --top_k 900 \
                                                                       --maxpn 16  --infer_patch_nums $args_infer_patch_nums \
                                                                       --depth 24
  

• Zero-shot transfer with 13 steps

  Modify args_infer_patch_nums between steps 8 and 14.

    args_infer_patch_nums="1_2_3_4_5_6_7_8_9_10_12_14_16"
    torchrun --nnodes=1 --nproc_per_node=2 --node_rank=0  eval_c2i.py  --batch_size 16  --cfg 2.5 --top_k 900 \
                                                                       --maxpn 16  --infer_patch_nums $args_infer_patch_nums \
                                                                       --depth 20
  

• Zero-shot transfer to 512x512

  Reference ground truth .npz file of 512x512

    args_infer_patch_nums="1_2_3_4_5_6_7_8_9_10_12_14_16_23_32"
    torchrun --nnodes=1 --nproc_per_node=2 --node_rank=0  eval_c2i.py  --batch_size 16  --cfg 3.0 --top_k 900 \
                                                                       --maxpn 16  --infer_patch_nums $args_infer_patch_nums \
                                                                       --depth 20
  

Acknowledgement

VAR

Llamagen

AiM