Polarization Imaging for Facial Recognition Enhancement System and Method

Abstract

A method for enhancing an image for facial recognition comprises capturing an image of the face with a polarizer and correcting the polarized image for non-uniformity. Stokes Parameters S 0 , S 1 , S 2 are obtained by weighted subtraction of the polarized image to form Stokes images. DoLP is computed from the Stokes images, and facial recognition algorithms are applied to the DoLP image. A system for enhancing images for facial recognition comprises a polarimeter configured to record polarized image data of a subject's face, a signal processing unit and logic configured to receive and store in memory the image data from the polarimeter, calculate Stokes parameters from the image data, and compute a DoLP image from the Stokes parameters.

What is claimed is: 
     
         1 . A method of obtaining enhanced images for facial recognition, the method comprising:
 recording raw image data of a subject's face to obtain a number of images;   correcting the images for non-uniformity;   calculating Stokes parameters S 0 , S 1 , and S 2  from the polarized images to create Stokes images by weighted subtraction of the polarized images; and   applying facial recognition algorithms to polarization images.   
     
     
         2 . The method of  claim 2 , wherein the step of recording raw image data of a subject's face to obtain a number of images is performed using a polarimeter. 
     
     
         3 . The method of  claim 2 , wherein the polarimeter comprises an objective lens, a polarization filter, and a focal plane array. 
     
     
         4 . The method of  claim 3 , wherein the focal plane array comprises a plurality of wire grid polarizers. 
     
     
         5 . The method of  claim 3 , wherein the focal plane array comprises a plurality of super pixels, each super pixel comprised of a 2×2 array that measures four (4) states of polarization, the states of polarization comprising 0°, 45°, 90°, and 135° states of linearly polarized light. 
     
     
         6 . The method of  claim 3 , wherein the focal plane array comprises a plurality of super pixels, each super pixel comprised of a three-pixel array that measures three (3) states of polarization, the states of polarization comprising 0°, 60° and 120° states of linearly polarized light. 
     
     
         7 . The method of  claim 3 , further comprising rotating the polarization filter and capturing images of the face with the filter at multiple orientations. 
     
     
         8 . The method of  claim 7 , wherein the multiple orientations comprise 0°, 45°, 90°, and 135°. 
     
     
         9 . The method of  claim 8 , wherein the images obtained at the multiple orientations are captured sequentially in time. 
     
     
         10 . The method of  claim 9 , wherein the images obtained at the multiple orientations are captured before the subject's face moves more than ¼ pixel. 
     
     
         11 . A system for enhancing images for facial recognition, comprising:
 a polarimeter configured to record polarized image data of a subject's face;   the system configured to record, with the polarimeter, raw image data of a subject's face to obtain a number of polarized images, the system further configured to correct the polarized images for non-uniformity, to calculate Stokes parameters S 0 , S 1 , and S 2  from the polarized images to create Stokes images by weighted subtraction of the polarized images; and to compute polarization images derived from the Stokes images.   
     
     
         12 . The system of  claim 11 , the system further configured to compute a Degree of Linear Polarization (DoLP) image from the Stokes parameters and apply facial recognition algorithms to the DoLP image. 
     
     
         13 . The system of  claim 11 , the polarimeter comprising an objective lens, a polarization filter, and a focal plane array. 
     
     
         14 . The system of  claim 13 , wherein the focal plane array comprises a plurality of wire grid polarizers. 
     
     
         15 . The system of  claim 13 , wherein the focal plane array comprises a plurality of super pixels, each super pixel comprised of a 2×2 array that measures four (4) states of polarization, the states of polarization comprising 0°, 45°, 90°, and 135° states of linearly polarized light. 
     
     
         16 . The system of  claim 13 , wherein the focal plane array comprises a plurality of super pixels, each super pixel comprised of a three-pixel array that measures three (3) states of polarization, the states of polarization comprising 0°, 60° and 120° states of linearly polarized light. 
     
     
         17 . The system of  claim 13 , wherein the polarization filter is a rotating filter and the logic is further configured to capture images of the face at multiple orientations of the rotating filter. 
     
     
         18 . The system of  claim 17 , wherein the multiple orientations comprise 0°, 45°, 90°, and 135°. 
     
     
         19 . The system of  claim 18 , further configured to capture the images of the multiple orientations sequentially in time. 
     
     
         20 . The system of  claim 19 , further configured to capture the images of the multiple orientations before the subject's face moves more than ¼ pixel.