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Towards interpretable image generation assessment: a exploration for structured multimodal approach

Feiyang Wang

DR-NTU (Nanyang Technological University), 2025

Abstract

Recent advances in diffusion models have led to impressive progress in text-to-image generation. However, while the visual fidelity of these models continues to improve, their semantic alignment with the input prompts—particularly in terms of object presence, relationships, and stylistic adherence—remains insufficiently evaluated. Existing automatic metrics such as CLIP-Score and FID focus on global embeddings and low- level statistics, failing to capture nuanced semantic correctness. This work presents a semantic evaluation framework for diffusion-generated images, powered by Multimodal Large Language Models (MLLMs) such as LLaVA-1.6/LLaVA- ov and Qwen2.5-VL. The workflow begins by extracting semantic dimensions (objects, attributes, relationships, styles) from prompts using NLP parsing and Semantic Role Labelling. It then dynamically constructs evaluation questions, guiding MLLMs to perform fine-grained image assessments in structured JSON format. From these responses, quantitative metrics are computed to evaluate semantic coverage, relation validity, stylistic consistency, and logical soundness. Experiments were conducted on images generated by SD (Stable Diffusion) model (SD-1.5 and SD-XL), along with three fine-tuned LoRA variants for each. The results demonstrate the framework’s ability to detect meaningful differences aligned with human judgment: SD-XL outperforms SD-1.5 in semantic coverage and relation validity by an average margin of 0.05–0.08 across all MLLM…

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