用语义特征空间匹配生成样本,显著提升图像生成质量。
Generate in Reconstruction Space, Match in Semantic Space: Transport Geometry for One-Step Generation

- 在语义特征空间中计算匹配距离,避免重建细节干扰
- ImageNet FID降低39倍,生成质量大幅提升
- 适合关注生成模型优化与特征选择的研究者
生成建模与自监督表征学习(SSL)优化的目标结构不同:生成训练强调分布保真,而SSL强调语义一致性。尽管近期研究反复发现SSL特征能提升生成效果,但其作用机制仍不明确。本文在单步生成框架下研究这一协同效应,其中表征角色明确:冻结的SSL特征用于将生成样本匹配到真实数据。我们采用Sinkhorn散度作为特征空间中的可计算近似,替代难以计算的Wasserstein距离,并通过Fréchet类评估指标(如FID)衡量总体分布差距。实验发现,当该目标在具有语义结构的SSL特征空间中计算时,性能显著提升(ImageNet FID降低39倍)。我们发现这主要源于匹配估计的改善:抑制无关重建细节的语义特征使分布几何更紧凑,从而更容易匹配。因此,最优训练用的SSL特征不必与评估指标使用的特征一致。例如,使用Inception作为特征提取器虽能降低FID,却会损害匹配稳定性和样本质量,揭示了一种“度量操纵”现象。我们在ImageNet上进行了大量实验,识别出表现最佳的SSL特征族,并证明匹配稳定性是筛选特征的重要量化标准。代码已开源。
原文摘要 · Abstract (English)
Generative modeling and self-supervised representation learning (SSL) optimize structurally different objectives: generative training rewards distributional fidelity, while SSL rewards semantic coherence. Yet recent work repeatedly finds that SSL features improve generative training, though the mechanism of this synergy remains unclear. Here, we study the benefits of SSL in generative modeling in the framework of one-step generation where the role of representation is explicit: frozen SSL features are used to match generated samples to real data. We use the Sinkhorn divergence in that feature space, providing a tractable surrogate for the Wasserstein distance, the population-level discrepancy approximated by Fréchet-style evaluation metrics (such as FID). We find that this objective becomes highly effective when computed in a semantically structured SSL feature space (a 39$\times$ reduction in ImageNet FID). We trace this behavior primarily to matching estimation: semantic SSL features that suppress nuisance reconstruction details induce a more compact geometry, making distribution matching more tractable. As a consequence, the best training SSL features need not match the features used by the evaluation metric. In particular, we show that using Inception as the feature extractor can improve FID while degrading matching stability and sample quality, revealing a form of metric hacking. Using extensive experiments on ImageNet, we identify which SSL feature families lead to best generation performance and show that matching stability is a quantitative criterion for selecting them. Code is available at https://github.com/Genentech/semantic-transport-generation.
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