RePiD: Efficient Recursive Pixel-Space Diffusion via Hierarchical Patch Denoising

Recent pixel-space generative models avoid the reconstruction bottleneck of latent diffusion, but direct denoising over high-dimensional pixel tokens remains computationally demanding. This paper studies a recursive alternative for efficient pixel-space diffusion. We propose RePiD, a hierarchical patch-level diffusion framework that recursively partitions an image and performs the core denoising computation on lower-dimensional pixel groups instead of repeatedly operating on full-resolution images. To preserve spatial coherence across patch-wise processing, RePiD introduces a neighborhood embedding module that conditions each patch on its surrounding regions. Experiments on class-to-image generation and unpaired image-to-image translation show that RePiD provides a favorable quality--efficiency trade-off for direct pixel-space generation. These results suggest that recursive patch-level denoising is a practical design direction for efficient pixel-space generative modeling. Our code is publicly available at \textcolor[HTML]{387FB9}{https://anonymous.4open.science/r/Recursive-Pixel-based-Diffusion-Model-1735}.