For more than a decade, computer graphics (CG) researchers and visual effects experts have been fascinated with bringing photorealistic digital actors to the screen. Crossing the well-known "uncanny valley" in CG humans has been one of the most difficult and crucial challenges, due to hypersensitivity to synthetic humans lacking even the slightest and most subtle features of genuine human faces. Given sufficient resources and time, photorealistic renderings of digital characters have been achieved in recent years. Some of the most memorable cases are seen in blockbuster movies, such as The Curious Case of Benjamin Button, Furious 7, and Rogue One: A Star Wars Story, in which large teams of highly skilled digital artists use cutting-edge digitization technologies. Despite the progress of 3D-scanning solutions, facial animation systems, and advanced rendering techniques, weeks of manual work are still needed to produce even just a few seconds of animation.
When depth cameras, such as structured light systems or time-of-flight sensors, were introduced, the 3D acquisition of highly deformable surfaces became possible. Graphics and vision researchers started to investigate the possibility of directly capturing complex facial performances, instead of manually key-framing them or applying complex simulations. While marker-based motion capture technologies are already widely adopted in industry, massive amounts of hand-tweaking and post-processing are still needed to generate lifelike facial movements. On the other hand, markerless solutions based on real-time RGB-D sensors provide dense and accurate facial shape measurements and were poised to automate and scale animation production.