Polarization imaging for facial recognition enhancement system and method
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.
1. A method of obtaining enhanced images for facial recognition, the method comprising:
recording, with a long wave infrared polarimeter, raw image data of a subject's face to obtain a number of polarized images;
correcting the polarized 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
computing polarization images derived from the Stokes images.
2. The method of claim 1 , wherein the step of computing polarization images derived from the Stokes images comprise computing a Degree of Linear Polarization (DoLP) image from the Stokes images.
3. The method of claim 1 , further comprising applying facial recognition algorithms to polarization images.
4. The method of claim 2 , wherein the polarimeter comprises an objective lens, a polarization filter, and a focal plane array.
5. The method of claim 4 , wherein the focal plane array comprises a plurality of wire grid polarizers.
6. The method of claim 4 , 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.
7. The method of claim 4 , 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.
8. The method of claim 4 , further comprising rotating the polarization filter and capturing images of the face with the filter at multiple orientations.
9. The method of claim 8 , wherein the multiple orientations comprise 0°, 45°, 90°, and 135°.
10. The method of claim 9 , wherein the images obtained at the multiple orientations are captured sequentially in time.
11. The method of claim 10 , wherein the images obtained at the multiple orientations are captured before the subject's face moves more than ¼ pixel.
12. A system for enhancing images for facial recognition, comprising:
a long wave infrared polarimeter configured to record polarized image data of a subject's face;
the system configured to record, with the long wave infrared 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.
13. The system of claim 12 , 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.
14. The system of claim 12 , the polarimeter comprising an objective lens, a polarization filter, and a focal plane array.
15. The system of claim 14 , wherein the focal plane array comprises a plurality of wire grid polarizers.
16. The system of claim 14 , 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.
17. The system of claim 14 , 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.
18. The system of claim 14 , 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.
19. The system of claim 17 , wherein the multiple orientations comprise 0°, 45°, 90°, and 135°.
20. The system of claim 18 , further configured to capture the images of the multiple orientations sequentially in time.
21. 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.