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We are working on even stronger base models and upgrading our training recipe ā stay tuned!
Introduction of CapRL
We are excited to introduce CapRL-3B, a lightweight 3B image captioner that achieves perception capabilities comparable to Qwen2.5-VL-72B.
This is the first study of applying Reinforcement Learning with Verifiable Rewards for the
open-ended and subjective image captioning task. Unlike traditional Supervised Fine-Tuning, which
can lead to models memorizing a limited set of annotated captions, our method allows the model to
explore and generate a broader range of creative and general descriptions.
CapRL is a new training paradigm featuring a decoupled two-stage pipeline. The initial
stage uses LVLMs to generate rich and accurate captions. Subsequently, the second stage evaluates
caption quality by using a vision-only LLM to perform the QA task. We also created a specific QA
curation pipeline to ensure the quality of the questions and answers used for the second stage.
By employing the CapRL training framework, initializing with the Qwen2.5-VL-3B model, and using a carefully
filtered 75K QA dataset as the training set, we obtained a highly capable captioner, CapRL-3B.
Key Features
- Remarkable visual understanding for Chart, Infographics and Document: CapRL-3B achieves perception accuracy and visual information coverage comparable to Qwen2.5-VL-72B.
- Well-organized output: The outputs of CapRL-3B are relatively well-structured, making them clear and easy to understand.
- Detailed description for natural images: The outputs of CapRL-3B can perfectly cover all valid visual information while containing fewer hallucinations.
Usage
If you want to use CapRL-3B for captioning, you can directly follow the exact same inference approach as in Qwen2.5-VL-series.
We recommend using vLLM to speed up inference.
Start an OpenAI API Service
Run the command below to start an OpenAI-compatible API service:
vllm serve "/PATH/CapRL-3B" \ --trust-remote-code \ --tensor-parallel-size=1 \ --pipeline-parallel-size=1 \ --gpu_memory_utilization=0.95 \ --served-model-name=caprl \ --port 8000 \ --host 0.0.0.0
Then you can use the chat API as below: (see OpenAI API protocol document for more details):
import base64from openai import OpenAI# Set OpenAI's API key and API base to use vLLM's API server.openai_api_key = "EMPTY"openai_api_base = "http://localhost:8000/v1"client = OpenAI( api_key=openai_api_key, base_url=openai_api_base,)image_path = "/path/to/local/image.png"with open(image_path, "rb") as f: encoded_image = base64.b64encode(f.read())encoded_image_text = encoded_image.decode("utf-8")base64_qwen = f"data:image;base64,{encoded_image_text}"chat_response = client.chat.completions.create( model="caprl", messages=[ {"role": "system", "content": "You are a helpful assistant."}, { "role": "user", "content": [ { "type": "image_url", "image_url": { "url": base64_qwen }, }, {"type": "text", "text": "What is the text in the illustrate?"}, ], }, ], temperature=1.0, max_tokens=max_tokens, top_p=1.0, extra_body={ "repetition_penalty": 1.0, },)print("Chat response:", chat_response)
Cases