1. Lien, J.: Automatic recognition of facial expressions using hidden markov models and estimation of expression intensity (1998)
2. Ye, J., Zhan, Y., Song, S.: Facial expression features extraction based on gabor wavelet transformation. In: IEEE International Conference on Systems, Man and Cybernetics, pp. 10–13 (2004)
3. Padgett, C., Cottrell, G.: Representing face images for emotion classification. MIT Press, Cambridge (1997)
4. Bartlett, M.: Face image analysis by unsupervised learning and redundancy reduction (1998)
5. Cootes, T.F., Edwards, G.J., Taylor, C.J.: Active appearance models. IEEE Transactions on Pattern Analysis and Machine Intelligence 23, 681–685 (2001)