Law of Vision Representation in MLLMs

October 6, 2025 · View on GitHub

arXiv / HuggingFace / More Thoughts (Blog in English) / More Thoughts (Blog in Chinese)

Visualization of the law

Updates

  • [2025/10/06] 🎉 Accepted by COLM 2025! Updated A score calculation with improved implementation.
  • [2024/09/01] We released the checkpoints of MLLMs on 13 vision representations.
  • [2024/08/29] We introduce the Law of Vision Representation in MLLMs and AC Policy.

Contents

Clone This Repository

git clone https://github.com/bronyayang/Law_of_Vision_Representation_in_MLLMs.git
cd Law_of_Vision_Representation_in_MLLMs

Train LLaVA with Custom Vision Representation

1. Install the LLaVA Environment: Ensure that the environment is compatible with your custom vision module

conda create -n ac_llava python=3.10 -y
conda activate ac_llava
pip install --upgrade pip
bash run.sh

This training environment has been tested on CUDA 12.2 and is compatible with all the encoders mentioned in the paper, except for OpenCLIP (refer to environment record for details on OpenCLIP compatibility).

To run SD3 vision representation, you'll need to install the diffusers package from the repository. Follow these steps:

cd diffusers
pip install -e .

Important Note:

To accommodate diffusion model encoders, this environment includes the diffusers, xformers, and transformers packages. However, these packages may conflict with each other. It is strongly advised to modify pyproject.toml and install only the packages required for your custom vision encoder, rather than all 10 encoders simultaneously.

2. Stage 1 Training

Prepare LLaVA Stage 1 Data: Follow the instructions in LLaVA's tutorial to prepare the data for Stage 1 training.

Start Training: Use the following command to start training:

bash llava/scripts/v1_5/train/pretrain.sh

However, before running the command, ensure that you modify the following parameters in the script:

  • --data_path
  • --image_folder
  • --output_dir
  • --vision_tower

Available Vision Towers:

  • openai/clip-vit-large-patch14
  • openai/clip-vit-large-patch14-336
  • laion/CLIP-ViT-L-14-laion2B-s32B-b82K
  • google/siglip-base-patch16-224
  • facebook/dinov2-large
  • runwayml/stable-diffusion-v1-5
  • stabilityai/stable-diffusion-2-1
  • lambdalabs/sd-image-variations-diffusers
  • stabilityai/stable-diffusion-xl-base-1.0
  • facebook/DiT-XL-2-512
  • stabilityai/stable-diffusion-3-medium-diffusers

Note: To combine features from multiple vision towers, use a dot . between the names. For example: openai/clip-vit-large-patch14.facebook/dinov2-large

3. Stage 2 Training

Prepare LLaVA Stage 2 Data: Follow the instructions in LLaVA's tutorial to prepare the data for Stage 2 training.

Start Training: Use the following command to start training:

bash llava/scripts/v1_5/train/finetune.sh

However, before running the command, ensure that you modify the following parameters in the script:

  • --data_path
  • --image_folder
  • --output_dir
  • --vision_tower
  • --pretrain_mm_mlp_adapter (checkpoint from Stage 1)

Pretrained Weights

If you prefer to use the same vision representations that we tested in our paper, we have released pretrained weights in Hugging Face for your convenience. This allows you to bypass the steps mentioned above and proceed directly to the next sections.

Evaluations

We use lmms-eval to evaluate the benchmark performance for MLLMs on various vision representations and to extract features from benchmark images for calculating the A score.

1. Install the lmms-eval Environment

cd llava/eval/lmms-eval
pip install -e .

2. Evaluate

To evaluate the model, use the following command:

accelerate launch --num_processes=8 -m lmms_eval --model llava   --model_args pretrained="path-to-stage-2-checkpoint"   --tasks task1 --batch_size 1 --log_samples --log_samples_suffix llava_custom_task1 --output_path ./logs/

For more information, refer to the original lmms-eval repository or the README in this repository.

AC Compute

1. Install the Environment for Computing AC Score

The environment setup is adapted from Telling Left from Right. If you encounter any issues, refer to the original repository and their issue tracker.

conda create -n ac_score python=3.9
conda activate ac_score
conda install pytorch=1.13.1 torchvision=0.14.1 pytorch-cuda=11.6 -c pytorch -c nvidia
conda install -c "nvidia/label/cuda-11.6.1" libcusolver-dev
cd C_score
pip install -e .

A Score

The A score measures the average negative log-likelihood of data passed through the vision encoder, trained projector, and LLM. It evaluates how well vision features align with the LLM after Stage 1 training.

Compute A Score: Add the --a_score flag to your stage 1 training command with pretrained projector loaded:

bash A_score/compute.sh

Before running, modify the following parameters in A_score/compute.sh:

  • --vision_tower
  • --pretrain_mm_mlp_adapter (checkpoint from Stage 1)
  • --image_folder

The A score will be computed over 100 datapoints without model updates or data shuffling, then printed automatically before training stops.

C Score

Prepare Vision Features on SPair-71k: First, download the SPair-71k dataset:

cd C_score
bash data/prepare_spair.sh

Extract features using command-line arguments:

python extract_feature.py \
    --input_path ./data/SPair-71k/JPEGImages \
    --output_path ./data/SPair-71k/features \
    --feature DINOv2

Arguments:

  • --input_path: Path to the SPair-71k dataset images (e.g., ./data/SPair-71k/JPEGImages)
  • --output_path: Path to save extracted features. Note: pck_train.py expects features to be stored in a directory that mirrors the input path structure with JPEGImages replaced by features (e.g., if images are in ./data/SPair-71k/JPEGImages, features should be in ./data/SPair-71k/features)
  • --feature: Vision representation to extract. Options: DIFT1.5, DIFT2.1, DIFTXL, IMDIFT, DiTDIFT, SD3DIFT, CLIP, OPENCLIP, DINOv2, SigLIP

Run the C Score Computation: Once the features are extracted, you can compute the C score with the following command:

python pck_train.py --config configs/eval_zero_shot_spair.yaml

The results will be logged.

If you wish to run feature combination, use the pck_train_two.py script and the configs/eval_zero_shot_spair_two.yaml configuration file, which concatenates features along the channel dimension.

AC Policy

Under Reconstruction...

Note

I aim to provide and maintain this repository in an easy-to-use form for everyone. However, please note that I am the sole maintainer of this codebase and have limited bandwidth. Before the process of cleaning up the code, I lost access to compute clusters and GPUs, which means some parts of the tutorial, such as environment setup and feature extraction, may be hardcoded or less than ideal, and the overall structure could be improved.

Make sure to reproduce the AC score in Appendix before you compute your own, and reflect any issue in GitHub. I would greatly appreciate any pull requests (PRs) to help enhance this repository. Your contributions are highly valued! Many thanks! ☺️

Citation

If you find this project useful, please cite our work:

@article{yang2024law,
  title={Law of Vision Representation in MLLMs},
  author={Yang, Shijia and Zhai, Bohan and You, Quanzeng and Yuan, Jianbo and Yang, Hongxia and Xu, Chenfeng},
  journal={arXiv preprint arXiv:2408.16357},
  year={2024}
}

Acknowledgement

  • LLaVA is the codebase we built upon, allowing us to easily add custom vision representations.
  • lmms-eval is an easy-to-use evaluation tool that enabled us to evaluate numerous benchmarks and extract features efficiently.
  • Telling Left from Right provides the correspondence computation on the SPair-71k dataset.