Training a shadow removal network using only 3D primitive occluders

Removing shadows in images is often a necessary pre-processing task for improving the performance of computer vision applications. Deep learning shadow removal approaches require a large-scale dataset that is challenging to gather. To address the issue of limited shadow data, we present a new and cost-effective method of synthetically generating shadows using 3D virtual primitives as occluders. We simulate the shadow generation process in a virtual environment where foreground objects are composed of mapped textures from the Places-365 dataset. We argue that complex shadow regions can be approximated by mixing primitives, analogous to how 3D models in computer graphics can be represented as triangle meshes. We use the proposed synthetic shadow removal dataset, DLSUSynthPlaces-100K, to train a feature-attention-based shadow removal network without explicit domain adaptation or style transfer strategy. The results of this study show that the trained network achieves competitive results with state-of-the-art shadow removal networks that were trained purely on typical SR datasets such as ISTD or SRD. Using a synthetic shadow dataset of only triangular prisms and spheres as occluders produces the best results. Therefore, the synthetic shadow removal dataset can be a viable alternative for future deep-learning shadow removal methods. The source code and dataset can be accessed at this link: https://neildg.github.io/SynthShadowRemoval/.