Real-time neural soft shadow synthesis from hard shadows

Soft shadows play a crucial role in enhancing visual realism in real-time rendering. Although traditional shadow mapping techniques offer high efficiency, they often suffer from artifacts and limited quality. In contrast, ray tracing can produce high-fidelity soft shadows but incurs substantial computational cost. In this paper, we propose a general-purpose, real-time soft shadow generation method based on neural networks. To encode shadow geometry, we employ the hard shadows via shadow mapping as input to our network, which effectively captures the spatial layout of shadow positions and contours. A lightweight U-Net architecture then refines this input to synthesize high-quality soft shadows in real time. The generated shadows closely approximate ray-traced references in visual fidelity. Compared to existing learning-based methods, our approach produces higher-quality soft shadows and offers improved generalization across diverse scenes. Furthermore, it requires no scene-specific precomputation, making it directly applicable to practical real-time rendering scenarios.