  Despite much progress, achieving real-time high-fidelity head avatar
animation is still difficult and existing methods have to trade-off between
speed and quality. 3DMM based methods often fail to model non-facial structures
such as eyeglasses and hairstyles, while neural implicit models suffer from
deformation inflexibility and rendering inefficiency. Although 3D Gaussian has
been demonstrated to possess promising capability for geometry representation
and radiance field reconstruction, applying 3D Gaussian in head avatar creation
remains a major challenge since it is difficult for 3D Gaussian to model the
head shape variations caused by changing poses and expressions. In this paper,
we introduce PSAvatar, a novel framework for animatable head avatar creation
that utilizes discrete geometric primitive to create a parametric morphable
shape model and employs 3D Gaussian for fine detail representation and high
fidelity rendering. The parametric morphable shape model is a Point-based
Morphable Shape Model (PMSM) which uses points instead of meshes for 3D
representation to achieve enhanced representation flexibility. The PMSM first
converts the FLAME mesh to points by sampling on the surfaces as well as off
the meshes to enable the reconstruction of not only surface-like structures but
also complex geometries such as eyeglasses and hairstyles. By aligning these
points with the head shape in an analysis-by-synthesis manner, the PMSM makes
it possible to utilize 3D Gaussian for fine detail representation and
appearance modeling, thus enabling the creation of high-fidelity avatars. We
show that PSAvatar can reconstruct high-fidelity head avatars of a variety of
subjects and the avatars can be animated in real-time ($\ge$ 25 fps at a
resolution of 512 $\times$ 512 ).
