用列表级奖励信息优化扩散模型,比成对比较更有效。
Beyond Pairwise Preferences: Listwise Reward-Aware Alignment for Diffusion Models

- 将多张图像的奖励分数转为优势权重,统一优化
- 在SD1.5和SDXL上超越现有基线方法
- 适合需要精细控制生成质量的研究者
偏好优化已成为对齐文本到图像扩散模型的高效替代方案,无需依赖在线人类反馈强化学习(RLHF)。然而,现有方法大多将监督信号简化为二元成对比较,限制了性能。当训练数据中同一提示存在多个候选图像,且连续奖励分数可提供比单一胜败标签更丰富的信息时,这种简化尤为不足。为此,我们提出Diffusion LAIR,一种面向扩散模型的奖励感知列表级偏好优化方法。针对每个提示,LAIR将一组候选图像的奖励分数转换为中心化优势权重,并在隐式奖励空间中优化优势加权回归目标——隐式奖励定义为当前模型相比固定参考模型的去噪损失改善量,同时引入二次惩罚项以控制隐式奖励的幅度。该目标同时利用所有候选图像,而非选择成对样本,且通过显式控制隐式奖励大小保持保守性。所提目标在隐式奖励空间中具有有界闭式解,明确揭示正则化强度如何调控偏好更新幅度。实验表明,Diffusion LAIR在SD1.5和SDXL上的文本到图像生成、组合生成及图像编辑任务中均优于强基线方法。
原文摘要 · Abstract (English)
Preference optimization has emerged as an efficient alternative to online reinforcement learning from human feedback (RLHF) for aligning text-to-image diffusion models. However, existing methods largely reduce supervision to binary pairwise comparisons. This pairwise reduction is limiting when training data naturally contains multiple candidate images for the same prompt, and when continuous reward scores can provide richer information than a single winner-loser label. To address these limitations, we propose Diffusion LAIR, a reward-aware listwise preference optimization method for diffusion models. For each prompt, LAIR converts reward scores across a group of candidate images into centered advantage weights, then optimizes an advantage-weighted regression objective on the implicit reward, defined as the denoising-loss improvement of the current model over a fixed reference model, with a quadratic penalty that regularizes the magnitude of the implicit reward. The resulting objective uses all candidates simultaneously rather than selecting pairs, and remains conservative by explicitly controlling the magnitude of the implicit reward. The LAIR objective admits a bounded closed-form optimum in implicit-reward space, clarifying how the regularization strength controls the magnitude of the preference update. Experiments show that Diffusion LAIR outperforms strong preference optimization baselines on SD1.5 and SDXL across text-to-image generation, compositional generation, and image editing benchmarks.
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