Extended depth-of-field biometric system

• US 9,495,590 B1
• Filed: 04/23/2015
• Issued: 11/15/2016
• Est. Priority Date: 04/23/2015
• Status: Expired due to Fees

• Current Assignee: Global Bionic Optics Ltd
• Original Assignee: Global Bionic Optics Ltd
• Inventors: Mathieu, Gilles
• Primary Examiner(s): Carter, Aaron W
• Application Number:
  US14/694,545
• Publication Number:
  US 20160314350A1
• Time in Patent Office: 572 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 27/0075 with means for altering, e.g. increasing, the depth of field or depth of focus
• CPC Class Codes: G06T 2200/21 involving computational photography
• CPC Class Codes: G06T 2207/20056 Discrete and fast Fourier transform, [DFT, FFT]
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: G06V 40/19 Sensors therefor
• CPC Class Codes: G06V 40/193 Preprocessing; Feature extraction
• CPC Class Codes: G06V 40/197 Matching; Classification
• CPC Class Codes: H04N 23/80 Camera processing pipelines; Components thereof
• CPC Class Codes: H04N 25/60 Noise processing, e.g. detecting, correcting, reducing or removing noise
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response

Abstract

An iris recognition system may include an optical system having an intentional amount of spherical aberration that results in an extended depth of field. A raw image of an iris captured by the optical system may be normalized. In some embodiments, the normalized raw image may be processed to enhance the MTF of the normalized iris image. An iris code may be generated from the normalized raw image or the enhanced normalized raw image. The iris code may be compared to known iris codes to determine if there is a match. In some embodiments, the iris code generated by the normalized iris image may be processed with equalization function before comparison with the known iris codes.

Claims

1. A method of processing an extended depth-of-field (EDOF) image of an iris at an imaging wavelength λ

_IM, comprising;

capturing a raw image of the iris, wherein the raw image has a reduced modulation transfer function (MTF) based on an optical system having an amount of spherical aberration (SA) of 0.2λ

_IM≦

SA≦

2λ

_IM;

normalizing the raw image; and

generating an iris code based on the normalized raw image, comprising performing an MTF enhancement of the normalized raw image in polar coordinates to generate a MTF enhanced image, comprising;

selecting a plurality of bands from the normalized raw image;

processing each of the bands to enhance the MTF; and

fusing the bands to generate the MTF enhanced image; and

generating the iris code from the MTF enhanced image.

2. The method of claim 1, further comprising storing the MTF enhanced image in an iris enrollment database.

3. The method of claim 1, wherein processing each of the bands to enhance the MTF comprises processing each band with a fast Fourier transform.

4. The method of claim 1, wherein processing each of the bands to enhance the MTF comprised processing each band with a kernel.

6. The method of claim 1, further comprising storing the raw image in an iris enrollment database.

7. The method of claim 1, further comprising storing the normalized raw image in an iris enrollment database.

8. The method of claim 1, further comprising storing the iris code in an iris enrollment database.

9. The method of claim 1, further comprising comparing the iris code to one or more known iris codes.

10. The method of claim 9, wherein the known iris codes were originally obtained by an optical system having no enhanced depth of field function.

11. The method of claim 9, wherein the known iris codes were originally obtained by an optical system having an enhanced depth of field function without MTF enhancement.

12. The method of claim 1, wherein the optical system comprises a single lens system.

13. The method of claim 12, wherein an aperture stop for the optical system is located at a position that minimizes comatic aberration.

14. The method of claim 12, wherein the single lens comprises glass or plastic.

15. The method of claim 12, wherein the single lens comprises a rotationally symmetric optical component.

16. The system of claim 12, wherein the single lens comprises a spherical refractive surface.

5. A method of processing an extended depth-of-field (EDOF) image of an iris at an imaging wavelength λ

_IM, comprising;

capturing a raw image of the iris, wherein the raw image has a reduced modulation transfer function (MTF) based on an optical system having an amount of spherical aberration (SA) of 0.2λ

_IM≦

SA≦

2λ

_IM;

normalizing the raw image;

generating an iris code based on the normalized raw image, wherein generating an iris code based on the normalized raw image comprises generating the iris code directly from the normalized raw image; and

generating an equalized iris code based on the iris code and iris code equalization coefficients;

wherein the iris code equalization coefficients have a base function covering a range of spatial frequency bands with related coefficients amplified according to a determined output MTF at related spatial frequencies.

33. The method of claim 5, further comprising storing the raw image in an iris enrollment database.

34. The method of claim 5, further comprising storing the normalized raw image in an iris enrollment database.

35. The method of claim 5, further comprising storing the iris code in an iris enrollment database.

36. The method of claim 5, further comprising comparing the iris code to one or more known iris codes.

37. The method of claim 36, wherein the known iris codes were originally obtained by an optical system having no enhanced depth of field function.

38. The method of claim 36, herein the known iris codes were originally obtained by an optical system having an enhanced depth of field function without MTF enhancement.

39. The method of claim 5, wherein the optical system comprises a single lens system.

40. The method of claim 39, wherein an aperture stop for the optical system is located at a position that minimizes comatic aberration.

41. The method of claim 39, wherein the single lens comprises glass or plastic.

42. The method of claim 39, wherein the single lens comprises a rotationally symmetric optical component.

43. The method of claim 39, wherein the single lens comprises a spherical refractive surface.

17. A system for processing an extended depth-of-field (EDOF) image of an iris at an imaging wavelength λ

_IM, comprising;

an optical system having an amount of spherical aberration (SA) of 0.2λ

_IM≦

SA≦

2λ

_IM, the optical system being configured to form on an image sensor a raw image having reduced a modulation transfer function (MTF) based on the spherical aberration;

a controller electrically connected to the image sensor, wherein the controller is configured to capture a raw image of the iris, normalize the raw image, and generate an iris code based on the normalized raw image, wherein the controller is configured to perform an MTF enhancement of the normalized raw image in polar coordinates to generate a MTF enhanced image, and generate the iris code from the MTF enhanced image, and wherein the controller is configured to select a plurality of bands from the normalized raw image, process each of the bands to enhance the MTF, and fuse the bands to generate the MTF enhanced image.

18. The system of claim 17, further comprising an iris enrollment database, wherein the controller is configured to transmit the MTF enhanced image to the iris enrollment database.

19. The system of claim 17, wherein the controller is configured to utilize a fast Fourier transform to process each of the bands to enhance the MTF.

20. The system of claim 17, wherein the controller is configured to utilize a kernel to process each of the bands to enhance the MTF.

22. The system of claim 17, further comprising an iris enrollment database, wherein the controller is configured to transmit the raw image to the iris enrollment database.

23. The system of claim 17, further comprising an iris enrollment database, wherein the controller is configured to transmit the normalized raw image to the iris enrollment database.

24. The system of claim 17, further comprising an iris enrollment database, wherein the controller is configured to transmit the iris code to the iris enrollment database.

25. The system of claim 17, wherein the controller is further configured to compare the iris code to one or more known iris codes.

26. The system of claim 25, wherein the known iris codes were originally obtained by an optical system having no enhanced depth of field function.

27. The system of claim 25, wherein the known iris codes were originally obtained by an optical system having an enhanced depth of field function without MTF enhancement.

28. The system of claim 17, wherein the optical system comprises a single lens system.

29. The system of claim 28, wherein an aperture stop for the optical system is located at a position that minimizes comatic aberration.

30. The system of claim 28, wherein the single lens comprises glass or plastic.

31. The system of claim 28, wherein the single lens comprises a rotationally symmetric optical component.

32. The system of claim 28, wherein the single lens comprises a spherical refractive surface.

21. A system for processing an extended depth-of-field (EDOF) image of an iris at an imaging wavelength λ

_IM, comprising;

an optical system having an amount of spherical aberration (SA) of 0.2λ

_IM≦

SA≦

2λ

_IM, the optical system being configured to form on an image sensor a raw image having reduced a modulation transfer function (MTF) based on the spherical aberration;

a controller electrically connected to the image sensor, wherein the controller is configured to capture a raw image of the iris, normalize the raw image, and generate an iris code based on the normalized raw image, wherein the controller is configured to generate the iris code directly from the normalized raw image, wherein the controller is further configured to generate an equalized iris code based on the iris code and iris code equalization coefficients, and wherein the iris code equalization coefficients have a base function covering a range of spatial frequency bands with related coefficients amplified according to a determined output MTF at related spatial frequencies.

44. The system of claim 21, further comprising an iris enrollment database, wherein the controller is configured to transmit the raw image to the iris enrollment database.

45. The system of claim 21, further comprising an iris enrollment database, wherein the controller is configured to transmit the normalized raw image to the iris enrollment database.

46. The system of claim 21, further comprising an iris enrollment database, wherein the controller is configured to transmit the iris code to the iris enrollment database.

47. The system of claim 21, wherein the controller is further configured to compare the iris code to one or more known iris codes.

48. The system of claim 47, wherein the known iris codes were originally obtained by an optical system having no enhanced depth of field function.

49. The system of claim 47, wherein the known iris codes were originally obtained by an optical system having an enhanced depth of field function without MTF enhancement.

50. The system of claim 21, wherein the optical system comprises a single lens system.

51. The system of claim 50, wherein an aperture stop for the optical system is located at a position that minimizes comatic aberration.

52. The system of claim 50, wherein the single lens comprises glass or plastic.

53. The system of claim 50, wherein the single lens comprises a rotationally symmetric optical component.

54. The system of claim 50, wherein the single lens comprises a spherical refractive surface.