View-Based Appearance Models
We can model the appearance of an object using a
Statistical Appearance Model.. If we wish to build a model of the
2D appearance of a 3D object, it will only be valid for a small range
of view points. To deal with this, we can build a set of models, one
for each distinct view point. In the case of the face, we show we
need only 5 models (two of which are reflections, so there are
only 3 distinct models) to be able to generate a face image from
any viewpoint from full left profile to full right profile
Profile Model
Mode 1: 
Mode 2:
Half-Profile Model
Mode 1: 
Mode 2: 
Frontal Model
Mode 1: 
Mode 2: 
animation
We are able to learn the relationship between viewing angle and
the model parameters, and thus can estimate head pose.
Such models can be fit to new images using the
Active Appearance Model algorithm.
We can use these models to
track
faces through wide angle rotations
Tim Cootes