Framestore began by searching for a suitable Hepburn double — someone, ideally, who would “share as many of her features and characteristics as possible.” Once identified, the doppelganger’s face was scanned using a facial action coding system that allowed Framestore to extract the muscle movements and textures needed to build a more faithful, CG Hepburn. Upon the completion of live shooting along the Amalfi Coast, the team returned to its in-house Capture Lab to further refine their actress’ face, smoothing out transitions and expressions for animation.
— Amar Toor, The Verge.