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PART|I Signal Processing, Modelling and Related Mathematical Tools
FIGURE 5.2 Facial features extracted for different facial expressions.
Whether using AUs or FAPs, most works rely on the results of
facial feature detection and tracking that have been described in Sec-
tion 5.2.3. We can see in Figure 5.2 the facial features extracted
with an AAM for different facial expressions. Thus, facial expres-
sion recognition consists in the classification of the facial features
movements using either spatial- or spatio-temporal classifiers [47].
Spatio-temporal classifiers commonly use hidden Markov models
[53, 54], whereas spatial classifiers typically use