arXiv Computer Vision By Ryugo Morita, Shunsuke Kitada, Stanislav Frolov, Brian Bernhard Moser, Ko Watanabe, Riku Takahashi, Jinjia Zhou, Andreas Dengel

Where Did the Light Come From? Diagnosing Cast-Shadow Reasoning in VLMs and Borrowing the Missing Shadow Prior from Image Generation Models

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The paper introduces ShadowBench, a benchmark built from real photographs that tests vision‑language models (VLMs) on three shadow‑related tasks: reading a visible shadow’s direction, inferring where a shadow should fall when absent, and judging physical consistency of shadows. Evaluations of 19 open VLMs and proprietary models show that while they can read shadow directions well, they perform poorly on inferring absent shadows and on consistency checks, with only Gemini‑3.1‑pro marginally above chance. The authors demonstrate that routing VLMs through image‑generation models (IGMs) significantly improves inference, suggesting that IGMs’ latent knowledge of illumination can bridge the gap between VLMs and physical reasoning.

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Oct 22

Where Did the Light Come From? Diagnosing Cast-Shadow Reasoning in VLMs and Borrowing the Missing Shadow Prior from Image Generation Models

The paper introduces ShadowBench, a benchmark built from real photographs that tests vision‑language models (VLMs) on three shadow‑related tasks: reading a visible shadow’s direction, inferring where a shadow should fall when absent, and judging physical consistency of shadows. Evaluation of 19 open VLMs and proprietary models shows that while they can read shadow direction well, they perform poorly on inferring absent shadows and judging consistency, with only Gemini‑3.1‑pro slightly above chance. The authors demonstrate that routing a VLM through an image‑generation model (IGM) provides the missing knowledge, significantly improving inference and highlighting the potential of image‑generation objectives for illumination‑aware VLMs.

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