Figure 3 shows the prototype being tested clinically. The light source is incoherent white light polarized by a polarization filter which obliquely illuminates a skin site. An optical flat on the skin surface provides optical coupling and a smooth surface so that specular reflectance from the glass/skin interface is reflected obliquely and misses the camera. Light scattered by the tissue is imaged by a camera which views the site through a polarization filter that can be aligned to collect light polarized either parallel or perpendicular relative to the source.
One image (Par) is taken with parallel orientation of the camera and one image (Per) is taken with perpendicular orientation. A new image is calculated pixel by pixel from the two acquired images: new image = (Par - Per)/(Par + Per). The numerator (Par - Per) subtracts out the 91% of randomly polarized light due to multiply scattered light from deep skin layers. Normalization by (Par + Per) causes cancelation of any common attenuation due to the skin pigmentation of melanin. Hence, the ratio clarifies pigmented lesions allowing the doctor to view the underlying tissue structure.