We present a fully automated system which unites CCD camera technology
with liquid crystal technology to create a polarization camera capabl
e of sensing the partial linear polarization of reflected light from o
bjects at pixel resolution. As polarization sensing not only measures
intensity but also additional physical parameters of light, it can the
refore provide a richer set of descriptive physical constraints for th
e understanding of images. Recently it has been shown that polarizatio
n cues can be used to perform dielectric/metal material identification
, specular and diffuse reflection component analysis, as well as compl
ex image segmentations that would be significantly more complicated or
even infeasible using intensity and color alone. Such analysis has so
far been done with a linear polarizer mechanically rotated in front o
f a CCD camera. The full automation of resolving polarization componen
ts using liquid crystals not only affords an elegant application, but
significantly speeds up the sensing of polarization components and red
uces the amount of optical distortion present in the wobbling of a mec
hanically rotating polarizer. In our system two twisted nematic liquid
crystals are placed in front of a fixed linear polarizer placed in fr
ont of a CCD camera. The application of a series of electrical pulses
to the liquid crystals in synchronization with the CCD camera video fr
ame rate produces a controlled sequence of polarization component imag
es that are stored and processed on Datacube boards. We present a sche
me for mapping a partial linear polarization state measured at a pixel
into hue, saturation and intensity producing a representation for a p
artial linear polarization image. Our polarization camera currently se
nses partial linear polarization and outputs such a color representati
on image at 5 Hz. The unique vision understanding capabilities of our
polarization camera system are demonstrated with experimental results
showing polarization-based dielectric/metal material classification, s
pecular reflection and occluding contour segmentations in a fairly com
plex scene, and surface orientation constraints.