Fast focus assessment system and method for imaging

• US 6,753,919 B1
• Filed: 11/24/1999
• Issued: 06/22/2004
• Est. Priority Date: 11/25/1998
• Status: Expired due to Term

• Current Assignee: Iridian Technologies, Inc. (Advent International Corporation)
• Original Assignee: Iridian Technologies, Inc. (Advent International Corporation)
• Inventors: Daugman, John G.
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): HANNETT, JAMES M
• Application Number:
  US09/449,295
• Time in Patent Office: 1,672 Days
• Field of Search: 348/78, 348/346, 348/349, 348/345, 267/354, 382/117, 396/18
• US Class Current: 348/345
• CPC Class Codes: G06V 40/18 Eye characteristics, e.g. of the iris
• CPC Class Codes: G06V 40/19 Sensors therefor
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

An imaging apparatus which can be used to capture high-quality iris images for identification of a person. The iris imager comprises a camera, a cold mirror, a lens, an illuminator, and a focus assessment processor. The imager has sensors and indicators which assist a user in aligning and focusing the device. The imager also automatically captures the image when proper positioning is achieved. The focus assessment processor accesses the image and applies certain measurement routines to assess the focus. The output of the focus assessment processor is used to control an indicator. A template representative of the iris features is extracted and then compared to a database of previously stored templates to identify the person.

Claims

1. A method of assessing the focus of an image, comprising the steps of:

convolving the image with a convolution kernel comprising;

(a) isolating one portion of a plurality of portions of said image;

(b) summing a central group of pixels of said portion to obtain a first sum;

(c) summing a plurality of outer pairs of rows and columns outside said central group of pixels to obtain a second sum;

(d) combining said first sum and said second sum in a predetermined ratio; and

(e) squaring the convolution result;

determining a spectral energy of said convolved image comprising;

(f) repeating steps (a)-(e) for further portions of said plurality of portions of said image and accumulating each said convolution result to generate a summation representative of said spectral energy; and

determining a focus score responsive to said spectral energy, said focus score being indicative of the focus of the image.

2. The method according to claim 1, wherein said step of determining said focus score comprises the step of nonlinearly compressing said summation.

3. The method according to claim 2, wherein said step of nonlinearly compressing said summation is of the form f(x)=100 x²/(x²+c²), thereby generating said focus score in a range between 0 and 100.

4. The method according to claim 1, wherein said predetermined ratio is −

3;

1, said first sum;

said second sum.

5. The method according to claim 1, further comprising the step of comparing said focus score to a predetermined threshold to assess said focus to determine a focus assessment.

6. The method according to claim 5, wherein if said focus score is not less than said predetermined threshold, then said focus assessment is determined to be acceptable, and if said focus score is less than said predetermined threshold, then said focus assessment is determined to be unacceptable.

7. The method according to claim 6, further comprising the step of activating an indicator responsive to said focus assessment.

8. A iris imaging apparatus for obtaining an image of an iris of an eye and for assessing the focus quality of the image, comprising:

a camera having a front surface and captures the image;

a lens having a image plane disposed in front of said front surface of said camera;

a mirror disposed on a side of said lens opposite said camera;

an illuminator disposed along a side of said mirror; and

a focus assessment processor coupled to said camera, said focus assessment processor comprising a microprocessor for convolving the image with a convolution kernel into a convolved image by (a) isolating one portion of a plurality of portions of said image;

(b) summing a central group of pixels of said portion to obtain a first sum;

(c) summing a plurality of outer pairs of rows and columns outside said central group of pixels to obtain a second sum;

(d) combining said first sum and said second sum in a predetermined ratio; and

(e) squaring the convolution result;

for determining a spectral energy of said convolved image by repeating steps (a)-(e) for further portions of said plurality of portions of said image and accumulating each said convolution result to generate a summation representative of said spectral energy; and

for determining a focus score responsive to said spectral energy, said focus score being indicative of the focus quality of the image.

9. The apparatus according to claim 8, further comprising an analog to digital converter and a frame buffer disposed between said camera and said focus assessment processor.

10. The apparatus according to claim 8, further comprising at least one of a visible indicator and an audible indicator, said focus assessment processor coupled to said at least one of a visible indicator and an audible indicator.

11. The apparatus according to claim 8, wherein said microprocessor comprises means for nonlinearly compressing said summation.

12. The apparatus according to claim 11, wherein said means for nonlinearly compressing said summation is of the form f(x)=100 x²/(x²+c²), thereby generating said focus score in a range between 0 and 100.

13. The apparatus according to claim 8, wherein said predetermined ratio is −

3;

1, said first sum;

said second sum.

14. The apparatus according to claim 8, further comprising means for comparing said focus score to a predetermined threshold to assess said focus to determine the focus quality.

15. The apparatus according to claim 14, wherein if said focus score is not less than said predetermined threshold, then the focus quality is determined to be acceptable, and if said focus score is less than said predetermined threshold, then the focus quality is determined to be unacceptable.

16. The apparatus according to claim 15, further comprising:

at least one of a visible indicator and an audible indicator, said focus assessment processor coupled to said at least one of a visible indicator and an audible indicator; and

means for activating said at least one of a visible indicator and an audible indicator responsive to the focus quality.

17. A system for assessing the focus quality of an image, comprising:

means for convolving the image with a convolution kernel comprising;

means for isolating one portion of a plurality of portions of said image;

an adder for summing a central group of pixels of said portion to obtain a first sum;

a second adder for summing a plurality of outer pairs of rows and columns outside said central group of pixels to obtain a second sum;

means for combining said first sum and said second sum in a predetermined ratio; and

means for squaring the convolution result;

means for determining a spectral energy of said convolved image comprising;

means for reactivating said means for convolving for further portions of said plurality of portions of said image and accumulating each said convolution result to generate a summation representative of said spectral energy; and

means for determining a focus score responsive to said spectral energy, said focus score being indicative of the focus quality of the image.

18. The system according to claim 17, wherein said means for determining said focus score comprises means for nonlinearly compressing said summation.

19. The system according to claim 18, wherein said means for nonlinearly compressing said summation is of the form f(x)=100 x²/(x²+c²), thereby generating said focus score in a range between 0 and 100.

20. The system according to claim 17, wherein said predetermined ratio is −

3;

1, said first sum;

said second sum.

21. The system according to claim 17, further comprising means for comparing said focus score to a predetermined threshold to assess said focus to determine the focus quality.

22. The system according to claim 21, wherein if said focus score is not less than said predetermined threshold, then the focus quality is determined to be acceptable, and if said focus score is less than said predetermined threshold, then the focus quality is determined to be unacceptable.

23. The system according to claim 22, further comprising:

at least one of a visible indicator and an audible indicator, and means for activating said at least one of a visible indicator and an audible indicator responsive to the focus quality.