1. A method for recognizing an emotion of an individual based on Action Units (AUs), the method comprising: receiving an input AU string including one or more AUs that represents a facial expression of an individual from an AU detector; comparing the input AU string with each of a plurality of AU strings, each of the plurality of AU strings includes a set of a same number of AUs that are most discriminative of a respective one of a plurality of emotions; identifying an AU string from the plurality of AU strings that best matches the input AU string; and outputting an emotion label corresponding to the best matching AU string that indicates the emotion of the individual.