Revisiting the Data Sampling in Multimodal Post-training from a Difficulty-Distinguish View

• URL: http://arxiv.org/abs/2511.06722v1
• Date: Mon, 10 Nov 2025 05:31:59 GMT
• Title: Revisiting the Data Sampling in Multimodal Post-training from a Difficulty-Distinguish View
• Authors: Jianyu Qi, Ding Zou, Wenrui Yan, Rui Ma, Jiaxu Li, Zhijie Zheng, Zhiguo Yang, Rongchang Zhao,
• Abstract summary: We propose two difficulty-aware sampling strategies for multimodal reasoning.<n>We show that Progressive Image Semantic Masking (PISM) quantifies sample hardness through systematic image degradation.<n>We also show that Cross-Modality Attention Balance (CMAB) assesses cross-modal interaction complexity.
• Score: 10.95044674432639
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Recent advances in Multimodal Large Language Models (MLLMs) have spurred significant progress in Chain-of-Thought (CoT) reasoning. Building on the success of Deepseek-R1, researchers extended multimodal reasoning to post-training paradigms based on reinforcement learning (RL), focusing predominantly on mathematical datasets. However, existing post-training paradigms tend to neglect two critical aspects: (1) The lack of quantifiable difficulty metrics capable of strategically screening samples for post-training optimization. (2) Suboptimal post-training paradigms that fail to jointly optimize perception and reasoning capabilities. To address this gap, we propose two novel difficulty-aware sampling strategies: Progressive Image Semantic Masking (PISM) quantifies sample hardness through systematic image degradation, while Cross-Modality Attention Balance (CMAB) assesses cross-modal interaction complexity via attention distribution analysis. Leveraging these metrics, we design a hierarchical training framework that incorporates both GRPO-only and SFT+GRPO hybrid training paradigms, and evaluate them across six benchmark datasets. Experiments demonstrate consistent superiority of GRPO applied to difficulty-stratified samples compared to conventional SFT+GRPO pipelines, indicating that strategic data sampling can obviate the need for supervised fine-tuning while improving model accuracy. Our code will be released at https://github.com/qijianyu277/DifficultySampling.

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