“…Whereas reflectance and shape are elemental properties of a face object, the appearance of a face is also subject to several other factors, including the facial expression and facial pose. In addition to these, various imaging parameters, such as exposure time, aperture, lens aberrations, and sensor spectral response also increase subject variations [11]. Nevertheless, the number of examples per person, that are available for learning, is often much smaller than the dimensionality of the image space.…”