Perceptual Contrast, Symmetry and Scale

For a computer based face recognition system to succeed, it must detect faces and the features that compose them despite variations each face has in the current scene [30]. Faces can be anywhere in an image, at a variety of sizes, at a variety of poses and at a variety of illuminations. Although humans quickly detect the presence and location of faces and facial features from a photograph, automatic machine detection of such objects involves a complex set of operations and tests. It is uncertain exactly how humans detect faces in an image, however we can attempt to imitate the perceptual mechanisms humans seem to employ. We begin by defining and discussing the significance of contrast, symmetry and scale in human vision. This will serve as a basis for the biologically motivated computational tools that we will be using. We then discuss our technique for the computational extraction of contrast information. The implementation of multi-scale analysis structure is then defined. Finally, two computational tools for obtaining information on symmetry are introduced: the symmetry transform and the selective symmetry detector.