  We introduce 3D Gaussian blendshapes for modeling photorealistic head
avatars. Taking a monocular video as input, we learn a base head model of
neutral expression, along with a group of expression blendshapes, each of which
corresponds to a basis expression in classical parametric face models. Both the
neutral model and expression blendshapes are represented as 3D Gaussians, which
contain a few properties to depict the avatar appearance. The avatar model of
an arbitrary expression can be effectively generated by combining the neutral
model and expression blendshapes through linear blending of Gaussians with the
expression coefficients. High-fidelity head avatar animations can be
synthesized in real time using Gaussian splatting. Compared to state-of-the-art
methods, our Gaussian blendshape representation better captures high-frequency
details exhibited in input video, and achieves superior rendering performance.
