High-Fidelity 3D Head Avatars Reconstruction through Spatially-Varying
  Expression Conditioned Neural Radiance Field
Minghan Qin Yifan Liu Yuelang Xu Xiaochen Zhao Yebin Liu Haoqian Wang
One crucial aspect of 3D head avatar reconstruction lies in the details of
facial expressions. Although recent NeRF-based photo-realistic 3D head avatar
methods achieve high-quality avatar rendering, they still encounter challenges
retaining intricate facial expression details because they overlook the
potential of specific expression variations at different spatial positions when
conditioning the radiance field. Motivated by this observation, we introduce a
novel Spatially-Varying Expression (SVE) conditioning. The SVE can be obtained
by a simple MLP-based generation network, encompassing both spatial positional
features and global expression information. Benefiting from rich and diverse
information of the SVE at different positions, the proposed SVE-conditioned
neural radiance field can deal with intricate facial expressions and achieve
realistic rendering and geometry details of high-fidelity 3D head avatars.
Additionally, to further elevate the geometric and rendering quality, we
introduce a new coarse-to-fine training strategy, including a geometry
initialization strategy at the coarse stage and an adaptive importance sampling
strategy at the fine stage. Extensive experiments indicate that our method
outperforms other state-of-the-art (SOTA) methods in rendering and geometry
quality on mobile phone-collected and public datasets.