  In this paper, we introduce FitMe, a facial reflectance model and a
differentiable rendering optimization pipeline, that can be used to acquire
high-fidelity renderable human avatars from single or multiple images. The
model consists of a multi-modal style-based generator, that captures facial
appearance in terms of diffuse and specular reflectance, and a PCA-based shape
model. We employ a fast differentiable rendering process that can be used in an
optimization pipeline, while also achieving photorealistic facial shading. Our
optimization process accurately captures both the facial reflectance and shape
in high-detail, by exploiting the expressivity of the style-based latent
representation and of our shape model. FitMe achieves state-of-the-art
reflectance acquisition and identity preservation on single "in-the-wild"
facial images, while it produces impressive scan-like results, when given
multiple unconstrained facial images pertaining to the same identity. In
contrast with recent implicit avatar reconstructions, FitMe requires only one
minute and produces relightable mesh and texture-based avatars, that can be
used by end-user applications.
