We present Bodyopt, a character skin deformation framework developed for Avatar: The Way of Water
. Our approach aims to learn the skin deformations from a given dataset and reproduce them reliably during shot production. In conjunction with the kinematic skeleton, we employ muscle fibers as an additional anatomical basis, where their length changes serve as a parametrization for the non-linear deformation components. We provide a novel way of curating the dataset to minimizing differences between similar poses, which would otherwise lead to a quality loss in the reconstruction. Our approach also handles runtime skin dynamics and utilities for artists to transfer deformations to new character types as well as extra modifiers for secondary motions like breathing. Additionally, we close the gap between final skin deformation and the representation used in Animation by providing a fast proxy solution that is based on the same input data.