title: The Cambridge Face Tracker: Accurate, Low Cost Measurement of Head Posture Using Computer Vision and Face Recognition Software.
abstract: OBJECTIVE
  We validate a video-based method of head posture measurement.
  
  
  METHODS
  The Cambridge Face Tracker uses neural networks (constrained local neural fields) to recognize facial features in video. The relative position of these facial features is used to calculate head posture. First, we assess the accuracy of this approach against videos in three research databases where each frame is tagged with a precisely measured head posture. Second, we compare our method to a commercially available mechanical device, the Cervical Range of Motion device: four subjects each adopted 43 distinct head postures that were measured using both methods.
  
  
  RESULTS
  The Cambridge Face Tracker achieved confident facial recognition in 92% of the approximately 38,000 frames of video from the three databases. The respective mean error in absolute head posture was 3.34°, 3.86°, and 2.81°, with a median error of 1.97°, 2.16°, and 1.96°. The accuracy decreased with more extreme head posture. Comparing The Cambridge Face Tracker to the Cervical Range of Motion Device gave correlation coefficients of 0.99 (P< 0.0001), 0.96 (P< 0.0001), and 0.99 (P< 0.0001) for yaw, pitch, and roll, respectively.
  
  
  CONCLUSIONS
  The Cambridge Face Tracker performs well under real-world conditions and within the range of normally-encountered head posture. It allows useful quantification of head posture in real time or from precaptured video. Its performance is similar to that of a clinically validated mechanical device. It has significant advantages over other approaches in that subjects do not need to wear any apparatus, and it requires only low cost, easy-to-setup consumer electronics.
  
  
  CONCLUSIONS
  Noncontact assessment of head posture allows more complete clinical assessment of patients, and could benefit surgical planning in future.
authors.affiliation: Department of Ophthalmology, Addenbrooke's Hospital, Cambridge, UK.
authors.forename: Peter B M
authors.initials: PB
authors.lastname: Thomas
authors.affiliation: Language Technologies Institute, Carnegie Mellon University, Pittsburgh, USA.
authors.forename: Tadas
authors.initials: T
authors.lastname: Baltrušaitis
authors.affiliation: Computer Laboratory, University of Cambridge, Cambridge, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Robinson
authors.affiliation: Department of Ophthalmology, Addenbrooke's Hospital, Cambridge, UK.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Vivian
keywords: computer vision; head posture; strabismus