TrueDepth measurements of facial expressions: Sensitivity to the angle between camera and face

Facial expressions play an important role in communication, especially in sign languages. Linguistic analysis of the exact contribution of facial expressions, as well as the creation of realistic conversational avatars, especially sign language avatars, requires accurate measurements of the facial expressions of humans while engaged in linguistic interaction. Several recent projects have employed a TrueDepth camera to make such measurements. The present paper investigates how reliable this technique is. In particular, we consider the extent to which the obtained measurements are affected by the angle between the camera and the face. Overall, we find that there are generally significant, and often rather substantial differences between measurements from different angles. However, when the measured facial features are highly activated, measurements from different angles are generally strongly correlated.