Multimodal Large Language Models (MLLMs) require high-resolution visual information to perform fine-grained perception, yet processing entire high-resolution images is computationally prohibitive. While recent methods leverage a Region-of-Interest (RoI) mechanism to focus on salient areas, they typically present a difficult trade-off: training-based approaches depend on large-scale annotated datasets, while training-free methods that utilize the model's internal attention are computationally inefficient and less accurate, requiring either multi-pass prefill stages or reliance on the slow auto-regressive decoding process. In this paper, we propose an efficient, annotation-free Self-Distilled Region Proposal Network (SD-RPN) that resolves this trade-off. The SD-RPN is built around a pipeline that transforms the noisy attention maps from the MLLM's middle layers into high-quality pseudo-RoI labels by explicitly denoising the signal and resolving ambiguity. We use these labels to train a lightweight Region Proposal Network (RPN) that learns a more precise localization. This RPN is also highly efficient, predicting the RoI in a single forward pass using features from the MLLM's middle layers, decoupling RoI identification from the auto-regressive generation and avoiding costly multi-pass operations. To validate our approach, we integrate the framework into multiple MLLM families. Despite being trained on only a few (e.g. 10K) question-answer pairs, our method demonstrates exceptional data efficiency and generalization, achieving over a 10% absolute accuracy improvement on unseen benchmarks, including TextVQA, DocVQA, and V-Star. Our work presents a practical and scalable solution for enhancing the fine-grained perception of MLLMs without requiring costly supervision or full model fine-tuning. Code is available at https://github.com/YuHengsss/SD-RPN.

翻译：多模态大语言模型（MLLMs）需要高分辨率视觉信息以执行细粒度感知，但处理完整的高分辨率图像在计算上是不可行的。尽管近期方法利用区域兴趣（RoI）机制聚焦于显著区域，但它们通常面临一个困难的权衡：基于训练的方法依赖于大规模标注数据集，而利用模型内部注意力的免训练方法则计算效率低下且准确性不足，需要多轮预填充阶段或依赖缓慢的自回归解码过程。本文提出一种高效、无需标注的自蒸馏区域建议网络（SD-RPN），以解决这一权衡。SD-RPN的核心是一个处理流程，通过显式去噪信号和消除歧义，将MLLM中间层产生的噪声注意力图转化为高质量伪RoI标签。我们利用这些标签训练一个轻量级区域建议网络（RPN），使其学习更精确的定位。该RPN同样高度高效，仅需单次前向传播，利用MLLM中间层的特征预测RoI，从而将RoI识别与自回归生成解耦，并避免了昂贵的多轮操作。为验证我们的方法，我们将该框架集成到多个MLLM家族中。尽管仅使用少量（例如10K）问答对进行训练，我们的方法展现出卓越的数据效率和泛化能力，在未见过的基准测试（包括TextVQA、DocVQA和V-Star）上实现了超过10%的绝对准确率提升。我们的工作为增强MLLMs的细粒度感知提供了一种实用且可扩展的解决方案，无需昂贵的监督或全模型微调。代码发布于 https://github.com/YuHengsss/SD-RPN。