提出一种无需训练的一阶采样器,显著提升低计算量下的生成质量。
Are First-Order Diffusion Samplers Really Slower? A Fast Forward-Value Approach
- 通过前向值预测修正采样点位置,改进一阶方法精度
- 在相同计算量下,样本质量优于或媲美高阶方法
- 适用于追求高效生成的图像合成场景
高阶常微分方程求解器已成为加速扩散概率模型(DPM)采样的标准工具,促使人们普遍认为一阶方法固有较慢,提升离散化阶数是加速主路径。本文挑战这一观点,从互补角度重新审视加速机制:除求解器阶数外,沿反向时间动力学中DPM评估点的位置对低神经函数评估次数(NFE)情形下的采样精度有显著影响。我们提出一种无需训练的一阶采样器,其主导离散化误差符号与DDIM相反。该方法通过廉价一步前瞻预测近似前向值评估。理论上,该采样器可证明逼近理想前向值轨迹,同时保持一阶收敛性。实验表明,在标准图像生成基准(CIFAR-10、ImageNet、FFHQ、LSUN)上,该采样器在相同NFE预算下持续提升样本质量,并可与甚至超越当前最优高阶采样器。结果表明,评估点位置为加速扩散采样提供了另一独立且重要的设计维度。
原文摘要 · Abstract (English)
Higher-order ODE solvers have become a standard tool for accelerating diffusion probabilistic model (DPM) sampling, motivating the widespread view that first-order methods are inherently slower and that increasing discretization order is the primary path to faster generation. This paper challenges this belief and revisits acceleration from a complementary angle: beyond solver order, the placement of DPM evaluations along the reverse-time dynamics can substantially affect sampling accuracy in the low-neural function evaluation (NFE) regime. We propose a novel training-free, first-order sampler whose leading discretization error has the opposite sign to that of DDIM. Algorithmically, the method approximates the forward-value evaluation via a cheap one-step lookahead predictor. We provide theoretical guarantees showing that the resulting sampler provably approximates the ideal forward-value trajectory while retaining first-order convergence. Empirically, across standard image generation benchmarks (CIFAR-10, ImageNet, FFHQ, and LSUN), the proposed sampler consistently improves sample quality under the same NFE budget and can be competitive with, and sometimes outperform, state-of-the-art higher-order samplers. Overall, the results suggest that the placement of DPM evaluations provides an additional and largely independent design angle for accelerating diffusion sampling.
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