PaCo-Reward-7B: A Pairwise Consistency Evaluator from the PaCo-RL Framework

       

This repository contains PaCo-Reward-7B, a key component of the PaCo-RL framework, as presented in the paper: PaCo-RL: Advancing Reinforcement Learning for Consistent Image Generation with Pairwise Reward Modeling

The PaCo-RL framework is designed for consistent image generation through reinforcement learning, aiming to preserve identities, styles, and logical coherence across multiple images for applications like storytelling and character design. PaCo-Reward-7B specifically acts as a pairwise consistency evaluator. It is trained on a large-scale dataset constructed via automated sub-figure pairing and evaluates consistency through a generative, autoregressive scoring mechanism, enhanced by task-aware instructions and Chain-of-Thought (CoT) reasoning.

• Project Page: https://x-gengroup.github.io/HomePage_PaCo-RL/
• Code Repository: https://github.com/X-GenGroup/PaCo-RL

🌟 Overview

PaCo-RL is a comprehensive framework for consistent image generation through reinforcement learning, addressing challenges in preserving identities, styles, and logical coherence across multiple images for storytelling and character design applications.

Key Components

• PaCo-Reward: A pairwise consistency evaluator with task-aware instruction and CoT reasoning.
• PaCo-GRPO: Efficient RL optimization with resolution-decoupled training and log-tamed multi-reward aggregation

Example Usage

PaCo-Reward-7B is fine-tuned based on Qwen/Qwen2.5-VL-7B-Instruct, so you can load the model similarly with the following code:

import torch
from transformers import Qwen2_5_VLForConditionalGeneration, AutoTokenizer, AutoProcessor
from qwen_vl_utils import process_vision_info

model = Qwen2_5_VLForConditionalGeneration.from_pretrained(
    "X-GenGroup/PaCo-Reward-7B", torch_dtype="bfloat16", device_map="auto"
)

# default processer
processor = AutoProcessor.from_pretrained("X-GenGroup/PaCo-Reward-7B")

image1 = 'https://huggingface.co/X-GenGroup/PaCo-Reward-7B/resolve/main/images/image_1.jpg'
image2 = 'https://huggingface.co/X-GenGroup/PaCo-Reward-7B/resolve/main/images/image_2.jpg'

main_prompt = 'Generate multiple images portraying a medical scene of a dentist in scrubs. The images should include activities such as explaining oral hygiene to a patient, taking X-rays of teeth, cleaning teeth in a dental office, and filling a cavity during an appointment. The setting should depict a realistic dental clinic.'
text_prompt = (
    f"Given two subfigures generated based on the theme: \"{main_prompt}\", "
    f"do the two images maintain consistency in terms of style, logic and identity? "
    f"Answer \"Yes\" and \"No\" first, and then provide detailed reasons."
)

# Example: Compare whether two images are visually consistent
messages_1 = [
    {
        "role": "user",
        "content": [
            {"type": "image", "image": image1},
            {"type": "image", "image": image2},
            {"type": "text", "text": text_prompt},
        ],
    }
]

# Preparation for inference
text = processor.apply_chat_template(
    messages_1, tokenize=False, add_generation_prompt=True
)
image_inputs, video_inputs = process_vision_info(messages_1)
inputs = processor(
    text=[text],
    images=image_inputs,
    videos=video_inputs,
    padding=True,
    return_tensors="pt",
)
inputs = inputs.to("cuda")

# Inference: Calculate consistency score
# Get logits for first token
with torch.no_grad():
    outputs = model(**inputs)
    first_token_logits = outputs.logits[0, -1, :]  # Last position of prompt

# Get token IDs for "Yes" and "No"
yes_id = processor.tokenizer.encode("Yes", add_special_tokens=False)[0]
no_id = processor.tokenizer.encode("No", add_special_tokens=False)[0]

# Calculate probability
yes_logit = first_token_logits[yes_id]
no_logit = first_token_logits[no_id]
yes_prob = torch.exp(yes_logit) / (torch.exp(yes_logit) + torch.exp(no_logit))

print(f"Consistency Score (Yes Conditional Probability): {yes_prob.item():.4f}")

# Inference: Generate detailed reasons
generated_ids = model.generate(**inputs, max_new_tokens=512)
generated_ids_trimmed = [
    out_ids[len(in_ids) :] for in_ids, out_ids in zip(inputs.input_ids, generated_ids)
]
output_text = processor.batch_decode(
    generated_ids_trimmed, skip_special_tokens=True, clean_up_tokenization_spaces=False
)
print(output_text[0])

🎁 Model Zoo

This model is part of a larger collection of models within the PaCo-RL framework. More related models can be found in the PaCo-RL Hugging Face collection.

Model	Type	HuggingFace
PaCo-Reward-7B	Reward Model	🤗 Link
PaCo-Reward-7B-Lora	Reward Model (LoRA)	🤗 Link
PaCo-FLUX.1-dev	T2I Model (LoRA)	🤗 Link
PaCo-FLUX.1-Kontext-dev	Image Editing Model (LoRA)	🤗 Link
PaCo-QwenImage-Edit	Image Editing Model (LoRA)	🤗 Link

⭐ Citation

If you find our work helpful or inspiring, please feel free to cite it:

@misc{ping2025pacorladvancingreinforcementlearning,
      title={PaCo-RL: Advancing Reinforcement Learning for Consistent Image Generation with Pairwise Reward Modeling}, 
      author={Bowen Ping and Chengyou Jia and Minnan Luo and Changliang Xia and Xin Shen and Zhuohang Dang and Hangwei Qian},
      year={2025},
      eprint={2512.04784},
      archivePrefix={arXiv},
      primaryClass={cs.CV},
      url={https://arxiv.org/abs/2512.04784}, 
}