1. A method of generating a feature descriptor for facial expression recognition, the method comprising: generating a plurality of gradient based images with different scales and orientations from a facial image; selecting a portion of an image corresponding to each action unit in each of the plurality of gradient based images; determining, by a processor, an appearance of at least one facial event in the selected portion of the image using coded appearance values; and determining a geometry of the at least one facial event in the selected portion of the image using a spin wheel structure to obtain a feature descriptor for each action unit for facial expression recognition.