Dual-Stage Value-Guided Inference with Margin-Based Reward Adjustment for Fast and Faithful VLMCaptioning

Despite significant advances in inference-time search for vision-language models (VLMs), existing approaches remain both computationally expensive and prone to unpenalized, low-confidence generations which often lead to persistent hallucinations. We introduce Value-guided Inference with Margin-based Reward (ViMaR)1, a two-stage inference framework that improves both efficiency and output fidelity by combining a temporal-difference value model with a marginaware reward adjustment. In the first stage, we perform a single pass to identify the highest-value caption among diverse candidates. In the second stage, we selectively refine only those segments that were overlooked or exhibit weak visual grounding, thereby eliminating frequently rewarded evaluations. A calibrated margin-based penalty discourages low-confidence continuations while preserving descriptive richness. Extensive experiments across multiple VLM architectures demonstrate that ViMaR generates captions that are significantly more reliable, factually accurate, detailed, and explanatory, while achieving over 4 speedup compared to existing value-guided methods. Specifically, we show that ViMaR trained solely on LLaVA Mistral-7B generalizes effectively to guide decoding in stronger unseen models. To further validate this, we adapt ViMaR to steer generation in both LLaVAOneVision-Qwen2-7B and Qwen2.5-VL-3B,