  Lightweight creation of 3D digital avatars is a highly desirable but
challenging task. With only sparse videos of a person under unknown
illumination, we propose a method to create relightable and animatable neural
avatars, which can be used to synthesize photorealistic images of humans under
novel viewpoints, body poses, and lighting. The key challenge here is to
disentangle the geometry, material of the clothed body, and lighting, which
becomes more difficult due to the complex geometry and shadow changes caused by
body motions. To solve this ill-posed problem, we propose novel techniques to
better model the geometry and shadow changes. For geometry change modeling, we
propose an invertible deformation field, which helps to solve the inverse
skinning problem and leads to better geometry quality. To model the spatial and
temporal varying shading cues, we propose a pose-aware part-wise light
visibility network to estimate light occlusion. Extensive experiments on
synthetic and real datasets show that our approach reconstructs high-quality
geometry and generates realistic shadows under different body poses. Code and
data are available at
\url{https://wenbin-lin.github.io/RelightableAvatar-page/}.
