Improvement in image contrast arising from the surface of a scattering medium, such as human tissue, can be achieved using polarization difference imaging and polarized light illumination. The image quality of the papillary ridges on the tips of fingers and thumbs (fingerprint) can be improved using any illuminating light.
When a scattering medium, such as tissue, is illuminated with polarized light, the image obtained in the backscattering direction contains two components: (1) a polarized component formed by photons that did not lose their polarization information (minimal scattering), and (2) the depolarized component formed by photons experiencing multiple scattering. The first component predominantly contains surface image information while the second, which is equally distributed in both polarization directions, contains subsurface image information. Subtraction of the perpendicular from the parallel image component leads to a new ‘image’ with enhanced contrast of surface structures, since the depolarized component is removed. This method can be used for optical fingerprint scanners. Optical fingerprinting for personal identification, can replace many existing and less reliable methods. Improving image contrast reduces false readings.