1. Ekman, P., Friesen, W.V., Hager, J.C.: Facial Action Coding System (FACS): Manual. A Human Face. Salt Lake City, USA (2002)
2. Ekman, P., Friesen, W.V., Hager, J.C., Ellsworth, P.: Emotion in the Human Face. Salt Lake City, USA (1972)
3. Tian, Y., Kanade, T., Cohn, J.F.: Recognizing Action units for facial expression analysis. IEEE Trans. Pattern Anal. Mach. Intell. 97–115 (2001)
4. Bartlett, M.S., Viola, P.A., Sejnowski, T.J., Golomb, B.A., Hager, J.C., Ekman, P.: Classifying facial action. IEEE Trans. Pattern Anal. Mach. Intell. 974–989 (1996)
5. Ersoy, Y.: Express Recognition: Exploring Methods of Emotion Detection. Stanford CS229 Stanford University (2013)